CC BY
1
DOI 10.18551/rjoas.2020-06.03
EFFECT OF SLOPES AND COMPOUND NPK FERTILIZER ON GROWTH AND YIELD OF MAIZE LOCAL VARIETIES, RELATIVE AGRONOMIC AND ECONOMIC FERTILIZER EFFECTIVENESS TO INCEPTISOL BUMELA, INDONESIA
Nurdin*
Doctorate Program of Agricultural Science, University of Brawijaya, Malang, Indonesia
Rayes Mochtar Lutfi, Soemarno, Sudarto
Department of Soil Science, Faculty of Agriculture, University of Brawijaya, Malang,
Indonesia
Musa Nikmah, Dunggio Muhajir
Department of Agrotechnology, Faculty of Agriculture, Gorontalo State University, Gorontalo,
Indonesia
*E-mail: nurdin@ung.ac.id
ABSTRACT
Maize cultivation has been carried out on the mountainous slopes with high fertilizer inputs, but maize productivity is still low. This study investigates the effect of slope and NPK compound fertilization as well as the best combination of growth and yield of local maize, relative agronomic effectiveness (RAE) percentage and economic fertilizer effectiveness (EFE) ratio in Inceptisol Bumela Indonesia. Slope variations (0-8, 8-15, 15-35, >35%) are combined with compound NPK fertilizer levels (0, 50, 100, 150, 200 kg ha-1) with split plot design. Growth data was recorded for changes in plant height and leaves number from 7 DAP to 42 DAP, while yield and yield components are recorded at harvest. The results showed that slope and NPK compound fertilization can increase the growth and yield of maize plants. The combination of flat slopes and fertilizer level of 100 kg ha-1 was the best combination in increasing plant height and the leaves number, accelerate the age of male and female flowering flowers, cob weight, grain yield and percentage of cob weight to grain yields. This combination was also able to increase the percentage of RAE, the ratio of EFE subsidized and non-subsidized. If farmers will continue to cultivate maize on the sloping land, it was recommended to arrive at hilly land with a fertilizer level of 100 kg ha-1 only.
KEY WORDS
Slope, fertilizer, NPK compound, growth, yield, maize.
Maize is an excellent commodity in Gorontalo province of Indonesia. Gorontalo Province maize production until 2018 has reached 1.7 million tons or increased by 9.3% from the previous year with a productivity of 5.0 t ha-1 (BPS, 2019) which places Gorontalo Province as one of the largest maize producers in Indonesia (Yunus et al., 2018 ). Maize was cultivated from generation to generation by local farmers (Ardiani, 2009; Fadhilah, 2013) using maize local varieties. However, since 2002 through the agropolitan programs with maize commodity (Jocom et al., 2009; Grace, 2010), the use of local varieties has changed to maize hybrid and composite varieties, so as the maize local varieties were rarely planted and threatened with extinction.
One of Gorontalo's local germplasm was the Motoro Kiki variety (Zubachtirodin and Kasim, 2012). Motoro Kiki is a Gorontalo maize local variety (Yasin et al., 2007) that aged 70-80 day after planting (DAP), yield potential was 3 t ha-1 of grain yield, resistant to downy mildew and leaf rust, and was well planted in the lowlands to the highlands (IAARD, 2009). Maize local has better growth than hybrid and maize composite, but the yield component shows the opposite patterns (Kaihatu and Pesireron, 2016).
Maize cultivation in Gorontalo Province region was very massive and has carried out on upland with a slope of 0% (flat) to mountainous land (slope >35%) which was vulnerable to land degradation. In fact, soil erosion that occurred from the Agropolitan maize planting area reported by Husain et al., (2004) as many as 1,396 t ha-1 year-1. If this condition was left, it will threaten the sustainability of maize farming. Upland for maize cultivation in Bumela Village was generally on Inceptisol (Indonesian Soil and Agroclimate Research Center Team, 1995). Inceptisol was a relatively young soil and its development was a level above of the Entisols (Rachim, 2007), including having a cambic horizons with a percentage of Na can be exchanged by 15% or more (Soil Survey Staff, 2014). Inceptisol has the potential to be developed (Nursyamsi et al., 2002; Hermawan et al., 2018) because it covers 70 million hectares in Indonesia (Kasno, 2009; Muyassir et al., 2012; Hermawan et al., 2018). However, these soils generally have low soil fertility and organic matter content (Abdurachman et al., 2008; Arviandi et al., 2015). Meanwhile, the high intensity of tillage for maize cultivation has led to a decrease in soil fertility (Lorenz et al., 2000; Husain et al., 2002; Pomalingo and Husain, 2003), so as the maize productivity is low, although fertilizer application exceeds recommendations.
A literature study on the results of the effect of slope and compound NPK fertilization combined with the specific growth and yield of maize local varieties has not been found. While information on the performance of growth and yield of maize local on various slopes combined with the level of NPK compound fertilization is very important for farmers and policy makers, especially in the Gorontalo Province. In fact, maize farmers continue to cultivate on sloping land of >25% with less fertilizer input or exceed the recommended fertilizer levels, so this research was important to done. This study aims to investigate the growth and yield of maize local variety of Motoro Kiki, the relative agronomic effectiveness (RAE) and economic fertilization effectiveness (EFE) on various slopes and NPK compound fertilization to Inceptisol Bumela, Indonesia.
MATERIALS AND METHODS OF RESEARCH
The study was conducted to four months (December 2019 to March 2020) on the toposequence of farmers maize land in Bumela Village, Bilato District, Gorontalo Regency, Gorontalo Province, Indonesia. Specifically geographical, the experimental field was rectangular located at 0o36'11.98"-0o36'11.46" N and 122o40'01.33"-122o40'02.49" E at an altitude of 314 m above sea level (m asl), and 0o36'08.39"-0o36'08.11" N and 122o40'00.31"-122o40'01.45" E with an altitude of 339 m asl.
Table 1 - Some soil physico-chemical properties were selected at a depth of 0-30 cm
No Soil properties Value Criterion*
1. Textures:
a. Sand (%) Silt (%) 62.00 Sandy clay
b. 21.50
c. Clay (%) 16.60
2. pH (H2O 5.65 Rather sour
3. Soil organic carbon (%) 0.67 Very low
4. Total nitrogen (%) 0.07 Very low
5. P-Bray 1 available (mg ka-1) 4.02 Low
6. Cations exchangeable:
a. K+ 0.29 Low
b. Na+ 2.16 Low
c. Ca2+ 3.86 Low
d. Mg+ 0.38 Low
7. Cation exchange capacity (cmol kg-1) 8.94 Low
8. Base saturation (%) 79.88 High
9. Na saturation (%) 24.27 High
Source: Eviyati and Soleman (2009).
This soil is very dark gray brownish (10YR 3/2), granular of soil structure and sandy clay of texture, cation exchange capacity of 8.94 cmol kg-1 and base saturation 79.88%, Na saturation of 24.17% (Table 1). Annual average rainfall of 1,245.90 mm with annual average temperature of 28.02°C (BWS Sulawesi II, 2019) and potential évapotranspiration of 152.95 mm, so the soil moisture regime was Ustic (106 dry days without humid days ) and the soil temperature regime was Isohyperthermic. Based on the morphology, soil physicochemical properties and other properties, the soil in the experimental field was classified as Oxic Humustepts (Soil Survey Staff, 2014).
The compound fertilizer used was NPK Phonska fertilizer with nutrient content (%) of 15-15-15 and Gorontalo maize local was used Motoro Kiki variety. The land was used upland owned by maize farmers with Inceptisol (Oxic Humustepts) soil type. This upland was used starting from flat (0-8%), undulating (8-15%), hilly (15-35%) and mountainous land (> 35%) on one toposequency.
The field experimental were designed following a split plot design. Four slope treatments were slope of 0-8% (S1), 8-15% (S2), 15-35% (S3) and slope >35% (S4) as the main plots. While the five NPK compound fertilizer treatments, namely 0 kg ha-1 (F0), 50 kg ha-1 (F1), 100 kg ha-1 (F2), 150 kg ha-1 (F3), and the level of 200 kg ha-1 (F4) as subplots. Each treatment was repeated three replication, so as 60 treatment plot combinations were obtained. The treatment plot was made 2 x 2 m by smoothing the soil evenly with hoe and shovel. The distance between plots was made 1 m to facilitate accessibility to and from the treatment plot.
Maize was planted with a distance of 20 x 40 cm in the planting hole of 2 maize seeds (December 26, 2019), so as to get 50 plant populations per plot. At the maize age of 7 day after planting (DAP), weed cleansing and thinning into 1 plant per holes. The first fertilization was done (1/2 level of fertilization per treatment) and plant embellishment was followed. Weed cleansing and embellishment was done when growing weeds manually with a hoe. At the maize age of 30 DAP, the second fertilization (the remaining 1/2 level of fertilization per treatment) was continued with plant embellishment. Maintenance continues until the harvest stage. Maize harvesting was done when the physical condition of the maize was dry and yellows (26 March 2020) or ± 90 DAP.
Observation of maize growth variables, including plant height (cm) and leaves number was carried out from plants aged 7 DAP to male flowers (± 42 DAP) on ten selected plants per plot. While the maize yield variables, including age of male and female flowering (DAP) were observed when maize flowers first appeared, the cob weight (t ha-1) was weighed after the maize seeds were separated from the cob, the grain yield (t ha-1) was weighed after the maize seeds were dried under 5 days sun exposure (± 15% moisture content) and the percentage of cob weight to grain yields (%).
NPK compound fertilizer applied, either singly or in combination was tested by relative agronomic effectiveness or RAE (Mackay et al., 1984; Chien, 1996) with the following equation:
Yt-Yo
RAE =-x 100
Ys - Yo
Where: Yt = maize yield on the tested fertilizer (t ha-1), Ys = maize yield standard (t ha-1), and Yo = maize yield on the control treatment (t ha-1). The greater the percentage of RAE, the better the effectiveness of fertilizer relative to agronomic traits. Meanwhile, to find out the fertilizer used has a good economic value, an economic fertilizer effectiveness (EFE) was carried out with the following equation:
p x Q
Ratio EFE = —-—
Where: P = price of maize per kg (IDR Kg-1), Q = total yield (kg ha-1), and C = price of fertilizer (IDR Ha-1). If the EFE ratio was >1, the fertilizer tested has good economic value (Saeri and Suwono, 2012; Wijaya et al., 2015).
The price of maize per kg in the study area was IDR 3,500. While the price of Phonska compound NPK fertilizer consists of two, namely NPK Phonska was subsidized by the government at a price of IDR 2,300 and non-subsidized at a price of IDR 8,000. The two forms of NPK fertilizer were used as a comparison material as well as consideration in making the best agronomic and economical NPK compound fertilizer selection decisions. All data obtained were analyzed with ANOVA of split plot design divided into patterns 45. If there was a treatment that has a significant effect, then it was continued with the Duncan Multiple Range Test (DMRT) at the test level P >0.05 with the tools of the Statistical Analysis System (SAS) program.
RESULTS AND DISCUSSION
Effect of slope and NPK compound fertilizer on maize growth. Slopes and NPK compound fertilization showed has significant effect on the plant height at the age of 14, 21, 28, 35, and 42 DAP, except at the age of 7 DAP in all treatments and at the age of 14 DAP in the treatment of compound NPK fertilizer that has not significantly affected (Table 2).
Table 2 - The average of plant height of maize local of Motoro Kiki varieties due to slopes and NPK compound fertilizer to Inceptisol Bumela, Indonesia
Plant Heigh (cm)
I I eatments 7 DAP 14 DAP 21 DAP 28 DAP 35 DAP 42 DAP
Slopes (S):
S1 (0 - 8%) 16.37 ± : 0.40ns 33.28 ±1.89ab 79.70 ± 4.31c 95.92 ± 6.48b 137.33 ± 4.49c 180.87 ± 10.48b
S2 (8 - 15%) 16.06 ± 0.38 34.97 ± 1.87b 69.99 ± 4.32b 83.90 ± 8.08a 120.67 ± 11.47ab 160.46 ± 13.22a
S3 (15 - 35%) 16.13 ± 0.40 32.36 ± 0.87a 63.41 ± 2.89a 89.26 ± 3.13a 113.94 ± 3.97a 159.33 ± 8.48a
S4 (>35%) 16.05 ± 0.62 33.02 ±1.23ab 68.77 ± 2.93b 99.01 ± 5.19b 127.07 ± 7.89b 160.52 ± 9.95a
NPK Compound (F):
F0 (0 kg ha-1) 16.45 ± 0.48ns 34.00 ± 0.65ns 69.80 ± 4.68ab 88.57 ± 11.43a 117.13 ± 12.57a 150.65 ± 10.18a
F1 (50 kg ha-1) 15.97 ± 0.17 33.31 ± 2.09 70.32 ± 8.59ab 92.70 ± 6.39ab 124.86 ± 10.99abc 164.78 ± 15.32b
F2 (100 kg ha-1) 16.33 ± 0.39 34.33 ± 2.88 72.38 ± 9.92b 96.53 ± 5.90b 131.45 ± 12.71c 173.05 ± 14.53b
F3 (150 kg ha-1) 15.97 ± 0.66 32.22 ± 0.71 66.72 ± 5.81a 88.65 ± 7.05a 121.95 ± 8.25ab 168.51 ± 7.38b
F4 (200 kg ha-1) 16.02 ± 0.36 33.16 ± 1.20 73.10 ± 6.42b 93.65 ± 10.16ab 128.36 ± 11.33bc 169.47 ± 11.83b
Combinations (SF):
S1F0 16.35 ± 0.49ns 33.55 ± 3.18abcd 76.55 ± 8.70abc 100.00 ± 17.11abc 134.50 ± 12.45abcd 163.95 ± 12.52cdef
S1F1 15.85 ± 0.92 32.75 ± 0.35abcd 81.75 ± 1.48ab 98.90 ± 1.84abcd 139.80 ± 5.66ab 187.65 ± 9.69ab
S1F2 16.50 ± 0.42 36.40 ± 4.81ab 84.45 ± 6.29a 102.70 ± 3.39ab 143.50 ± 7.07a 190.60 ± 6.93a
S1F3 16.95 ± 3.89 31.65 ± 5.30bcd 73.95 ± 13.79abcd 89.55 ± 18.60bcde 132.00 ± 4.38abcde 178.75 ± 13.22abcd
S1F4 16.20 ± 1.13 32.05 ± 2.90bcd 81.80 ± 4.53ab 88.45 ± 1.63bcde 136.85 ± 4.31abc 183.40 ± 3.54abc
S2F0 16.20 ± 0.00 34.40 ± 5.37abcd 67.45 ± 8.56cdef 73.30 ± 10.89f 107.30 ± 13.01 h 139.20 ± 13.15g
S2F1 16.20 ± 1.13 36.35 ± 2.90abc 71.50 ± 3.54bcdef 85.10 ± 3.54cdef 118.10 ± 2.97defgh 158.15 ± 2.76efg
S2F2 16.55 ± 0.21 37.20 ± 3.68a 76.15 ±1.63abc 95.70 ± 1.27abcde 138.95 ± 16.33ab 174.45 ± 16.19abcde
S2F3 15.60 ± 1.56 32.40 ± 0.42abcd 64.70 ±1.98cdef 81.10 ± 1.41ef 120.90 ± 7.64cdefgh 165.55 ± 2.05cdef
S2F4 15.75 ± 0.21 34.50 ± 1.13abcd 70.15 ± 6.01 bcdef 84.30 ± 3.82def 118.10 ± 10.89defgh 164.95 ± 2.90cdef
S3F0 16.10 ± 0.42 33.35 ± 2.76abcd 66.05 ±1.48cdef 87.30 ± 0.99cdef 108.50 ±1.27gh 148.95 ± 4.60fg
S3F1 16.00 ± 0.00 31.55 ± 2.05cd 61.80 ± 10.18ef 89.85 ± 3.89bcde 115.30 ± 3.68efgh 158.40 ± 10.75efg
S3F2 16.55 ± 0.78 31.50 ± 0.99d 62.20 ± 3.54def 88.80 ± 2.97bcde 114.90 ± 2.69efgh 172.05 ± 8.70abcde
S3F3 15.55 ± 1.06 33.15 ±1.06abcd 60.15 ± 3.32f 86.10 ± 0.28cdef 111.90 ± 0.57fgh 161.45 ± 4.88def
S3F4 16.45 ± 1.06 32.25 ± 2.90bcd 66.85 ±1.63cdef 94.25 ± 2.76abcde 119.10 ± 0.99defgh 155.80 ± 0.85efg
S4F0 17.15 ± 0.78 34.70 ± 0.57abcd 69.15 ± 3.04cdef 93.70 ± 5.66abcde 118.25 ± 14.07defgh 150.50 ± 7.50fg
S4F1 15.85 ± 0.35 32.60 ± 1.13abcd 66.25 ± 2.62cdef 96.95 ± 5.87abcd 126.25 ± 12.52abcdefg 154.95 ± 1.77efg
S4F2 15.75 ± 0.35 32.25 ± 2.33bcd 66.75 ± 4.17cdef 98.95 ± 5.16abcd 128.45 ± 13.65abcdef 155.10 ± 11.60efg
S4F3 15.80 ± 0.28 31.70 ± 0.42bcd 68.10 ± 5.94cdef 97.85 ± 7.57abcd 123.00 ± 8.91 bcdefgh 168.30 ± 7.21 bcdef
S4F4 15.70 ± 0.57 33.85 ±1.48abcd 73.60 ± 3.54abcde 107.60 ± 14.42a 139.40 ± 28.43ab 173.75 ± 27.08abcde
CV (%) 7.18 5.88 6.93 6.75 5.84 5.05
Note: Mean ± standard deviation, DAP: day after planting, ns: not significant, CV: coefficient of variant, Values sharing same letters differ non-significantly at Duncan Multiple Range Test (P > 0.05).
This was be fathomed because it was not directly related to the plant physiological aspects, but directly related to soil characteristics. Slopes were closely related to the quantity of soil organic carbon, total N, and enzyme activity by changing the rate of litter decomposition and soil microbial activity (Nahidan et al., 2015). The highest rate of plant height increase at the age of 28 DAP with an average percentage of plant height increase of 111.05% in all treatments and decreased until the age of 42 DAP. While, the highest rate of plant height increase with an average percentage of plant height increase of 70.56% was indicated by the slope 0% (flat) and NPK compound fertilizer as much as 50 kg ha-1, while the rate of plant height increase was lowest with an average percentage of plant height increase of 58.12% only was shown by the slopes >35% (mountainous) and NPK compound fertilizer as much as 0 kg ha-1.
Apparently, the effect of slopes began to be seen clearly in plant height from the age of 14 DAP to 42 DAP, where the flat slope had a significant effect on plant height and the peak
effect of the slope was more pronounced at plant height aged of 35 and 42 DAP, followed by a undulating slope. The position of the slope has a significant effect on the maize growth (Changere and Lal, 1997). Hilly and mountainous slopes will receive more sunlight than undulating and flat slopes, so that decomposition of organic matter and nutrient cycling was better. Humidity is a basic environmental factor in a relatively dry area, so higher humidity at the shady slopes location can lead to better nutrition cycles and higher microbial community activity (Xue et al., 2018). The levels of C-organic, total N, P are available and K can be exchanged at the study site is relatively low (Table 1), so fertilizing action was needed. While the effect of NPK compound fertilizer began to be seen clearly in plant height later on from the age of 21 DAP to 42 DAP, where the fertilizing level of 100 kg ha-1 showed the highest plant height from the age of 28 DAP, 35 and 42 DAP, but it was not significantly different from the fertilizer level of 50 kg ha-1 and 200 kg ha-1 at the age of 21 DAP, 28, 35 and 42 DAP, except with fertilizer levels 0 kg ha-1 and 150 kg ha-1 were significantly different at the age of 28 DAP and 35 DAP. The NPK fertilization has a significant effect on the agronomic parameters of maize (Achiri et al., 2017). Nitrogen is another important soil nutrient that affects plant growth and water use efficiency (Sardans et al., 2008). The application of Phosphor fertilizer increases the efficient utilization of N fertilizer on the production of maize biomass (Mensah and Mensah, 2016). Potassium is needed for maize growth (Solihin et al., 2019).
The combination of slopes and NPK compound fertilizers began to showing a significant effect on plant height aged of 14 DAP to 42 DAP, while at age of 7 DAP had no significant effect (Table 2). The combination of flat slope (0-8%) to undulating slope (8-15%) with NPK fertilizer compound level of 100 kg ha-1 shows the highest plant height at the age of 21 DAP to 42 DAP. While on a combination of hilly slopes (15-35%) and mountainous slopes ( 35%) with all levels of fertilization was relatively varied. However, if the lands with these slopes will still be used for maize cultivation, then it will be sought only to land with hilly slopes (15-35%) combined with NPK compound fertilizer levels of 100 kg ha-1 because plant height reaches of 174.45 cm at age of 42 DAP. At low fertilization rates, the amount of N and K absorbed by plants increases with the amount of fertilizer applied (Niu et al., 2013). Maize plants absorb large amounts of N from the soil at V6 and maximum absorption occurs before silking (Ma' et al., 2003).
The effect of the slope on the leaves number shows the significant effect from the age of 7 DAP to 42 DAP, while the effect of compound NPK fertilization shows the significant effect later starting at age of 21 DAP to 42 DAP (Table 3). The highest rate of leaves number increasing occurred at the age of 14 DAP with an average percentage of leaves number increase of 79.70% in all treatments and decreased until the age of 42 DAP. The rate of increasing the leaves number with an average percentage leaves number increase by 38.16% was indicated by the slopes >35% (mountainous) and NPK compound fertilizer as much as 150 kg ha-1, while the rate of increasing the leaves number with an average the percentage of leaves number increase was 29.94% only, as indicated by the slopes 15-35% (hilly) and NPK compound fertilizer as much as 200 kg ha-1. Leaves number of maize increased significantly as the plants aged with NPK fertilizing (Titah et al., 2016). Effect of slope on the leaves number at age of 7 DAP shows the highest leaves number on hilly slopes (15-35%) and not significantly different from flat slopes (0-8%) and undulating slopes (8-15%), but significantly different from slopes mountainous (>35%). At the age of 14 DAP, the effect of hilly slopes still shows the highest leaves number and was significantly different from flat slopes and undulating slopes, while those with mountainous slopes are not significantly different. At the age of 21 DAP and 28 DAP, the effect of flat slope has shown the highest leaves number and was significantly different from all slope classes, except at the age of 28 DAP which was only significantly different from hilly slopes. While at the age of 35 DAP and 42 DAP, the effect of mountainous slopes shows the highest leaves number and was not significantly different from flat slopes.
The effect of NPK compound fertilizer on the leaves number at the age of 7 DAP shows the highest leaves number at the fertilizer level of 200 kg ha-1, while at the age of 14 DAP the highest leaves number at the fertilizer level of 50 kg ha-1, although at the two ages it was not
significantly different from all fertilization levels. At the age of 21 DAP, NPK compound fertilization shown has significant effect with the highest leaves number at the fertilizer level of 50 kg ha-1 and significantly different from the fertilizer level of 0 kg ha-1 only. While at the age of 28 DAP to 42 DAP, the effect of compound NPK fertilizer on the most leaves number was indicated by the fertilizer level of 100 kg ha-1 and significantly different from the fertilizer level of 0 kg ha-1 only, except at age of 35 DAP apart from being significantly different from the level 0 kg ha-1 also with a fertilizer level of 50 kg ha-1.
Table 3 - The average of number leaves of maize local of Motoro Kiki varieties due to slopes and NPK
compound fertilizer to Inceptisol Bumela, Indonesia
Leaves Number (strands)
Treatments 7 DAP 14 DAP 21 DAP 28 DAP 35 DAP 42 DAP
Slopes (S):
S1 (0 - 8%) 3.26 ± 0.12b 5.33 ± 0.09a 8.32 ± 0.38a 9.68 ± 0.52b 10.99 ± 0.23c 12.24 ± 0.38bc
S2 (8 - 15%) 3.22 ± 0.08b 5.78 ± 0.20b 8.00 ± 0.15b 9.40 ± 0.38b 10.49 ± 0.48b 11.70 ± 0.46a
S3 (15 - 35%) 3.34 ± 0.15b 6.02 ± 0.22c 7.91 ± 0.18b 9.07 ± 0.29a 10.22 ± 0.28a 12.02 ± 0.40b
S4 (>35%) 2.99 ± 0.11a 5.83 ± 0.06bc 7.90 ± 0.29b 9.50 ± 0.34b 11.01 ± 0.33c 12.51 ± 0.53c
NPK Compound (F):
F0 (0 kg ha-1) 3.22 ± 0.06ns 5.70 ± 0.32ns 7.73 ± 0.21a 8.88 ± 0.25a 10.22 ± 0.41a 11.43 ± 0.25a
F1 (50 kg ha-1) 3.15 ± 0.15 5.87 ± 0.31 8.18 ± 0.55b 9.48 ± 0.54b 10.55 ± 0.54b 12.21 ± 0.51b
F2 (100 kg ha-1) 3.23 ± 0.23 5.70 ± 0.20 8.07 ± 0.22b 9.63 ± 0.43b 10.93 ± 0.27c 12.38 ± 0.19b
F3 (150 kg ha-1) 3.13 ± 0.21 5.65 ± 0.29 8.06 ± 0.02b 9.51 ± 0.23b 10.87 ± 0.48c 12.33 ± 0.24b
F4 (200 kg ha-1) 3.26 ± 0.22 5.77 ± 0.44 8.10 ± 0.15b 9.53 ± 0.28b 10.80 ± 0.42bc 12.21 ± 0.66b
Combinations (SF):
S1F0 3.30 ± 0.00abc 5.25 ± 0.07e 8.00 ± 0.28cde 9.10 ± 0.42cdef 10.60 ± 0.42abc 11.65 ± 0.64cde
S1F1 3.20 ± 0.14abc 5.45 ± 0.21cde 8.95 ± 0.49a 10.25 ± 1.06a 11.15 ± 0.49ab 12.65 ± 0.49ab
S1F2 3.45 ± 0.21ab 5.40 ± 0.14cde 8.40 ± 0.28b 10.20 ± 0.14ab 11.15 ± 0.64ab 12.40 ± 0.57abc
S1F3 3.20 ± 0.42abc 5.25 ± 0.21e 8.10 ± 0.42cde 9.50 ± 0.28abcde 11.00 ± 0.14ab 12.40 ± 0.57abc
S1F4 3.15 ± 0.21abc 5.30± 0.28de 8.15 ± 0.35bcd 9.35 ± 0.64cdef 11.05 ± 0.49ab 12.10 ± 0.28bcd
S2F0 3.20 ± 0.28abc 5.70 ± 0.14bcde 7.80 ± 0.00efg 8.75 ± 0.21ef 9.95 ± 0.07e 11.15 ± 0.07e
S2F1 3.30 ± 0.14abc 6.10 ± 0.42ab 8.15 ± 0.21bcd 9.45 ± 0.07bcde 10.05 ± 0.07de 11.50 ± 0.14de
S2F2 3.15 ± 0.07abc 5.85 ± 0.21abcd 7.90 ± 0.00def 9.70 ± 0.85abcd 11.05 ± 0.78ab 12.25 ± 1.06bcd
S2F3 3.15 ± 0.21abc 5.65 ± 0.07bcde 8.05 ± 0.07cde 9.50 ± 0.28abcde 10.85 ± 0.07abc 12.10 ± 0.14bcd
S2F4 3.30 ± 0.14abc 5.60 ± 0.14bcde 8.10 ± 0.00cde 9.60 ± 0.57abcd 10.55 ± 0.21bcd 11.50 ± 0.42de
S3F0 3.25 ± 0.49abc 5.95 ± 0.49abc 7.60 ± 0.14g 8.60 ± 0.14f 9.80 ± 0.28e 11.30 ± 0.28e
S3F1 3.15 ± 0.07abc 6.10 ± 0.28ab 8.00 ± 0.28cde 9.00 ± 0.00def 10.15 ± 0.07de 12.20 ± 0.14bcd
S3F2 3.40 ± 0.14ab 5.75 ± 0.35bcde 8.00 ± 0.14cde 9.20 ± 0.00cdef 10.55 ± 0.07bcd 12.25 ± 0.35bcd
S3F3 3.35 ± 0.07abc 5.95 ± 0.21abc 8.05 ± 0.07cde 9.25 ± 0.07cdef 10.25 ± 0.07de 12.20 ± 0.14bcd
S3F4 3.55 ± 0.07a 6.35 ± 0.07a 7.90 ± 0.14def 9.30 ± 0.00cdef 10.35 ± 0.21cde 12.15 ± 0.07bcd
S4F0 3.15 ± 0.07abc 5.90 ± 0.14abc 7.55 ± 0.07g 9.10 ± 0.00cdef 10.55 ± 0.21bcd 11.65 ± 0.49cde
S4F1 2.95 ± 0.07bc 5.85 ± 0.21abcd 7.65 ± 0.07fg 9.25 ± 0.07cdef 10.85 ± 0.07abc 12.50 ± 0.28ab
S4F2 2.95 ± 0.07bc 5.80 ± 0.28abcde 8.00 ± 0.14cde 9.45 ± 0.07bcde 11.00 ± 0.14ab 12.65 ± 0.07ab
S4F3 2.85 ± 0.07c 5.75 ± 0.07bcde 8.05 ± 0.21cde 9.80 ± 0.14abcd 11.40 ± 0.14a 12.65 ± 0.64ab
S4F4 3.05 ± 0.21abc 5.85 ± 0.07abcd 8.25 ± 0.07bc 9.90 ± 0.14abc 11.25 ± 0.21a 13.10 ± 0.28a
CV (%) 6.39 4.01 1.54 3.48 2.32 2.71
Note: Mean ± standard deviation, DAP: day after planting, CV: coefficient of variant, Values sharing same letters differ non-significantly at Duncan Multiple Range Test (P > 0.05).
The combination of slope and compound NPK fertilizer shows a significant effect on the leaves number starting at age of 7 DAP to 42 DAP (Table 3). The combination of hilly slopes with NPK compound fertilizer of 200 kg ha-1 level shows the highest leaves number at the age of 7 DAP to 14 DAP and was significantly different with the combination of mountainous slopes with fertilizer levels of 50, 100 and 150 kg ha-1 at age of 7 DAP only, as well as a combination of flat slope and fertilizer level of 0 kg ha-1 to 200 kg ha-1, a combination of undulating slopes with fertilizer levels of 0 kg ha-1, 150 and 200 kg ha-1, a combination of hilly and mountainous slopes with levels 100 kg ha-1. While at the age of 21 DAP, the highest leaves number was indicated by a combination of flat slope and 50 kg ha-1 fertilizer level that was significantly different from all treatment combinations. The same pattern was also shown by the highest leaves number at the age of 28 DAP on a combination of flat slope and 50 kg ha-1 fertilizer level, but significantly different from the twelve other treatment combinations. At the age of 35 DAP, the effect of mountainous slopes with fertilizer level of 150 kga ha-1 combination showed the highest leaves number and was significantly different from nine other treatment combinations, whereas at age of 42 DAP the highest leaves number was indicated by a combination of mountainous slopes with a fertilizer level of 200 kg ha- 1 and significantly different from thirteen other treatment combinations.
Effect of slopes and NPK compound fertilizer on maize yields. The effects of slopes and compound NKP fertilizers show a significant effect on all yield components (Table 4). On
the flat slope (0-8%), the male flowers (42.21 DAP) and the female maize flowers (47.64 DAP) were the most significantly different from the other slopes, while on the hilly slopes (1535%) the male flowers were the longest (45.84 DAP) and female flowers (49.31 DAP). The highest of cob weight and grain yields on the flat slope (0-8%) that it was significantly different from other slopes, except that the cob weight was not significantly different from other slopes. The highest of cob weight percentage ton grain yield was shown by mountainous slopes (>35%) and has not significantly different from flat slopes. The slope position also has a significant effect on maize yield (Changere and Lal, 1997), as the slope and organic fertilizer have a significant and very significant effect on potato yield (Wati et al., 2014). The 10-22% lower content of organic matter, nitrogen, and phosphorus on the lower middle slope is associated with a decrease in maize yield of 27% compared to the position of the upper middle slope (Wezel et al., 2002).
The effect of NPK compound fertilizer on the age of male and female maize flowers was the fastest out (44.87 DAP and 48.22 DAP respectively) and the highest cob weight was shown by the fertilizer level of 100 kg ha-1 which was significantly different with the level of fertilizer 0 kg ha-1 only. While the highest of grain yields hass shown by the fertilizer level of 200 kg ha-1 but not significantly different from the fertilizer level of 100 kg ha-1, whereas the highest of cob weight percentage to grain yield was indicated by the level of 50 kg ha-1 and significantly different with the level of 0 kg ha-1 and 200 kg ha-1 only. The NPK fertilization has a significant effect on maize yield parameters (Achiri et al., 2017). Flowering time can often be accelerated 3-10 days by application of NPK fertilizer (Gumeleng, 2003). Female maize flowering were most quickly obtained at the fertilizer level of 250 kg ha-1 N, 100 kg ha-1 P and 75 kg ha-1 K whereas the latest were obtained at 0 kg ha-1 level (Nurdin et al., 2009). Phosphor is able to increase the photosynthesis process which will further influence the increase in dry weight of plants (Minardi, 2002).
Table 4 - The average of component yield of maize local of Motoro Kiki varieties due to slopes and NPK compound fertilizer to Inceptisol Bumela, Indonesia
Treatments Male Flowering Age (DAP) Female Flowering Age (DAP) Cob Weight (t ha-1) Grain Yields (t ha-1) Percentage of Cob Weight to Grain Yields (%)
Slopes (S):
S1 (0 - 8%) 44.21 ± 0.84a 47.64 ± 0.70a 1.78 ± 0.27ns 3.06 ± 0.25c 20.43 ± 2.39a
S2 (8 - 15%) 45.53 ± 0.49b 48.92 ± 0.70b 1.51 ± 0.37 2.48 ± 0.37ab 22.49 ± 2.93ab
S3 (15 - 35%) 45.84 ± 0.54b 49.31 ± 0.74b 1.70 ± 0.31 2.56 ± 0.47b 24.27 ± 3.37b
S4 (>35%) 45.53 ± 0.77b 48.82 ± 0.86b 1.55 ± 0.29 2.18 ± 0.33a 25.31 ± 4.14b
NPK Compound (F):
F0 (0 kg ha-1) 45.92 ± 1.17b 49.57 ± 1.24a 1.19 ± 0.24a 2.15 ± 0.46a 20.36 ± 2.20a
F1 (50 kg ha-1) 45.01 ± 1.01ab 48.42 ± 0.85b 1.65 ± 0.31b 2.41 ± 0.49a 26.37 ± 3.77b
F2 (100 kg ha-1) 44.87 ± 1.14a 48.22 ± 1.15b 1.81 ± 0.26b 2.87 ± 0.50bc 23.03 ± 5.23ab
F3 (150 kg ha-1) 45.25 ± 0.57ab 48.59 ± 0.58b 1.74 ± 0.18b 2.49 ± 0.21ab 24.19 ± 1.49ab
F4 (200 kg ha-1) 45.34 ± 0.43ab 48.57 ± 0.49b 1.78 ± 0.12b 2.93 ± 0.34c 21.66 ± 1.62a
Combinations (SF):
S1F0 44.25 ± 1.63bcd 47.75 ±1.81bcd 1.48 ± 0.42abcde 2.80 ± 0.67abcd 19.71 ± 0.85cde
S1F1 43.50 ± 0.28cd 47.17 ± 0.28cd 2.08 ± 0.21ab 3.23 ± 0.42ab 21.21 ± 3.68abcde
S1F2 43.35 ± 0.12d 46.80 ± 0.05d 1.49 ± 0.68abcde 3.20 ± 0.18ab 16.94 ± 7.83e
S1F3 44.52 ± 1.06bcd 47.86 ± 0.94bcd 1.87 ± 0.32abc 2.78 ± 0.06abcd 23.50 ± 3.25abcde
S1F4 45.42 ± 0.49abcd 48.61 ± 0.54abcd 1.95 ± 0.03abc 3.30 ± 0.11a 20.77 ± 1.29abcde
S2F0 45.98 ± 1.15ab 49.85 ± 1.01ab 0.92 ± 0.13e 2.04 ± 0.42de 18.08 ± 5.14de
S2F1 45.67 ± 0.71ab 48.91 ± 0.68abc 1.35 ± 0.25bcde 2.18 ± 0.67cde 25.93 ± 1.17abcde
S2F2 44.71 ± 0.68abcd 47.90 ± 0.61 bcd 1.77 ± 0.05abcd 2.91 ± 0.47abcd 23.06 ± 5.15abcde
S2F3 45.48 ± 0.45abc 48.83 ± 0.33abcd 1.76 ± 0.44abcd 2.48 ± 1.03abcde 23.83 ± 5.83abcde
S2F4 45.80 ± 0.90ab 49.08 ± 0.82abc 1.73 ± 0.47abcd 2.79 ± 0.45abcd 21.58 ± 0.97abcde
S3F0 46.65 ± 0.26a 50.46 ± 0.38a 1.28 ± 0.10cde 1.99 ± 0.24de 23.33 ± 1.86abcde
S3F1 45.30 ± 1.79abcd 48.65 ±1.72abcd 1.59 ± 0.14abcde 2.19 ± 0.44cde 28.87 ± 3.52abc
S3F2 46.00 ± 0.57ab 49.51 ± 0.73ab 2.13 ± 0.02a 3.22 ± 0.39ab 22.42 ± 2.67abcde
S3F3 45.86 ± 0.94ab 49.23 ± 0.94abc 1.83 ± 0.01abcd 2.30 ± 0.34bcde 26.38 ± 3.49abcd
S3F4 45.38 ± 0.07abcd 48.70 ± 0.00abcd 1.67 ± 0.17abcd 3.09 ± 0.46abc 20.32 ± 0.93bcde
S4F0 46.80 ± 0.42a 50.20 ± 0.33a 1.09 ± 0.38de 1.76 ± 0.46e 20.30 ± 0.78bcde
S4F1 45.55 ± 0.49abc 48.95 ± 0.26abc 1.57 ± 0.27abcde 2.05 ± 0.36de 29.48 ± 0.81ab
S4F2 45.43 ± 0.52abc 48.65 ± 0.45abcd 1.83± 0.09abcd 2.16 ± 0.10cde 29.71 ± 3.46a
S4F3 45.11 ± 0.68abcd 48.41 ± 0.59abcd 1.48 ± 0.12abcde 2.38 ± 0.23abcde 23.08 ± 1.32abcde
S4F4 44.75 ± 1.58abcd 47.90 ±1.84bcd 1.77 ± 0.07abcd 2.53 ± 0.39abcde 23.96 ± 3.55abcde
CV (%) 1.88 1.77 18.54 18.53 16.34
Note: Mean ± standard deviation, DAP: day after planting, CV: coefficient of variant, Values sharing same letters differ non-significantly at Duncan Multiple Range Test (P > 0.05).
The combination of slope and NPK compound fertilizer shows a significant effect on all yield components (Table 4). The combination of flat slope with NPK compound fertilizer level of 100 kg ha-1 shows the age of male and female maize flowering fastest and has significantly different from the ten slope combinations and fertilizer level at age of male maize
flowering, and significantly different from the eight slope combinations and other fertilizer levels at age of female maize flowering. Meanwhile, the highest of cob weight was shown by a combination of hilly slopes and fertilizer level of 100 kg ha-1 which was significantly different from four other treatment combinations only. The highest of grain yiled was shown by the combination of flat slope and fertilizer level of 200 kg ha-1, but it was significantly different from only eight other treatment combinations. Whereas the highest of cob weight percentage to grain yiled was shown by the combination of mountainous slopes with a fertilizer level of 100 kga ha-1 and significantly different from five other treatment combinations only. The best combination of slope and NPK compound fertilizer on maize yield parameters was flat slope with fertilizer level of 100 kg ha-1. This was in line with the report of Ngosong et al., (2019) that N fertilizing between 50 and 100 kg N ha-1 was optimal for maize production in Cameroon's volcanic soil.
Relative agronomic and economic fertilization effectiveness. The highest of relative agronomic effectiveness (RAE) values, the ratio of economic fertilization effectiveness (EFE) with subsidized fertilizer and non-subsidized was shown by flat slopes (0-8%) which differ significantly by undulating slopes (8-15%) and mountainous slopes (>35%) on RAE, significantly different from all slopes in the EFE subsidized and non-subsidized ratio (Table 5), in other to the distribution was obtained following the RAE pattern S1> S3> S2> S4. Provision of standard or recommended of NPK Fertilizers (300 kg ha-1 NPK+250 kg ha-1 Urea) shows a higher RAE value (100) than other fertilizer doses to maize plants (Kasno, 2010; Wijaya et al., 2015; Erselia et al., 2017; Subandi et al., 2017), in sugarcane (Zulkarnain et al., 2017). Furthermore, the highest of the RAE value, EFE subsidized and non-subsidized ratio with NPK compound fertilization was shown by fertilizer level of 200 kg ha-1 which was not significantly different with fertilizer level of 50 kg ha-1 and 100 kg ha-1 at RAE, and has not significantly different only with the level of 100 kg ha-1 in the EFE subsidized and non-subsidized ratio, so as the distribution was obtained following the pattern F4> F2> F3> F1> F0.
Table 5 - Relative agronomic effectiveness (RAE) and economic fertilizer effectiveness (EFE) of maize yields with NPK compound fertilizer to Inceptisol Bumela, Indonesia
Treatments Grain Yields RAE Ratio of EFE Ratio of EFE
(t ha-1) (%) (Subsidized Fertilizer) (Non-Subsidized Fertilizer)
Slopes (S):
S1 (0 - 8%) 3.06 ± 0.25c 131.98 ± 127.63a 4.66 ± 0.38a 1.34 ± 0.11a
S2 (8 - 15%) 2.48 ± 0.37ab 45.77 ± 38.99b 3.77 ± 0.57bc 1.08 ± 0.16bc
S3 (15 - 35%) 2.56 ± 0.47b 56.24 ± 55.19ab 3.89 ± 0.85b 1.12 ± 0.24b
S4 (>35%) 2.18 ± 0.33a 33.55 ± 24.19b 3.31 ± 0.46c 0.95 ± 0.13c
NPK Compound (F):
F0 (0 kg ha-1) 2.15 ± 0.46a 0.00 ± 0.00c 3.26 ± 0.69c 0.94 ± 0.20c
F1 (50 kg ha-1) 2.41 ± 0.49a 68.50 ± 98.78abc 3.66 ± 0.84c 1.05 ± 0.24c
F2 (100 kg ha-1) 2.87 ± 0.50bc 111.47 ± 70.62ab 4.36 ± 0.75ab 1.26 ± 0.22ab
F3 (150 kg ha-1) 2.49 ± 0.21ab 28.69 ± 28.59bc 3.79 ± 0.32bc 1.09 ± 0.09bc
F4 (200 kg ha-1) 2.93 ± 0.34c 125.77 ± 87.65a 4.45 ± 0.51a 1.28 ± 0.15a
Combinations (SF):
S1F0 2.80 ± 0.67abcd 0.00 ± 338.69c 4.26 ± 1.01abcd 1.23 ± 0.29abcd
S1F1 3.23 ± 0.42ab 216.57 ± 215.72ab 4.91 ± 0.65ab 1.41 ± 0.19a
S1F2 3.20 ± 0.18ab 201.63 ± 93.48abc 4.87 ± 0.28ab 1.40 ± 0.08ab
S1F3 2.78 ± 0.06abcd -12.33 ± 31.98c 4.23 ± 0.10abcd 1.22 ± 0.03abcd
S1F4 3.30 ± 0.11a 254.05 ± 58.19a 5.02 ± 0.17a 1.44 ± 0.05a
S2F0 2.04 ± 0.42de 0.00 ± 44.09c 3.10 ± 0.64de 0.89 ± 0.18de
S2F1 2.18 ± 0.67cde 14.41 ± 69.87bc 3.31 ± 1.02cde 0.95 ± 0.29cde
S2F2 2.91 ± 0.47abcd 90.14 ± 49.05abc 4.42 ± 0.72abcd 1.27 ± 0.21abcd
S2F3 2.48 ± 1.03abcde 46.41 ± 107.49abc 3.78 ± 1.57abcde 1.09 ± 0.45abcde
S2F4 2.79 ± 0.45abcd 77.91 ± 46.97abc 4.24 ± 0.68abcd 1.22 ± 0.20abcd
S3F0 1.99 ± 0.24de 0.00 ± 23.75c 3.03 ± 0.36de 0.87 ± 0.10de
S3F1 2.19 ± 0.44cde 19.93 ± 44.03bc 3.33 ± 0.68cde 0.96 ± 0.19cde
S3F2 3.22 ± 0.39ab 121.84 ± 38.66abc 4.90 ± 0.59ab 1.41 ± 0.17ab
S3F3 2.30 ± 0.34bcde 30.75 ± 33.48bc 3.50 ± 0.51bcde 1.01 ± 0.15bcde
S3F4 3.09 ± 0.46abc 108.67 ± 45.97abc 4.69 ± 0.71abc 1.35 ± 0.20abc
S4F0 1.76 ± 0.46e 0.00 ± 37.02c 2.67 ± 0.70e 0.77 ± 0.20e
S4F1 2.05 ± 0.36de 23.07 ± 29.31bc 3.11 ± 0.55de 0.89 ± 0.16de
S4F2 2.16 ± 0.10cde 32.28 ± 8.21bc 3.28 ± 0.15cde 0.94 ± 0.04cde
S4F3 2.38 ± 0.23abcde 49.93 ± 18.84abc 3.62 ± 0.36abcde 1.04 ± 0.10abcde
S4F4 2.53 ± 0.39abcde 62.46 ± 31.35abc 3.85 ± 0.59abcde 1.11 ± 0.17abcde
CV (%) 18.53 160.21 18.52 18.57
Note: Mean ± standard deviation, CV: coeficient of variant, Values sharing same letters differ non-significantly at Duncan Multiple Range Test (P > 0.05).
The highest of RAE, the EFE subsidized and non-subsidized ratio in the combination of slope and NPK compound fertilization has shown by the combination of flat slope with fertilizer level 200 kg ha-1 which was significantly different from the ten other treatment combinations at RAE value and significantly different from eight other treatment combinations at the EFE subsidized and non-subsidized ratio (Table 5). While the lowest RAE value was indicated by the combination of flat slope with fertilizer level of 150 kg ha-1 which was significantly different from the combination of flat slope and fertilizer level of 50 kg ha-1 only, the EFE subsidized and non-subsidized ratio was indicated by the combination of mountainous slopes with fertilizer level of 0 kg ha-1 and significantly different from ten other treatment combinations. Thus, the combination of a flat slope with a fertilizer level of 100 kg ha-1 is the best combination that can be applied by maize farmers. This was in line with the report of Wijaya et al. (2015) that fertilizing urea at 100 kg ha-1, SP-36 at 200 kg ha-1 and KCl at 100 kg ha-1 showed the highest EFE ratio in both subsidized and non-subsidized fertilizers. However, if farmers will continue to maize cultivating on sloping land, it was recommended to arrive at hilly slopes (15-35%) with fertilizer levels of 100 kg ha-1 only.
CONCLUSION
The slope and NPK compound fertilization can increase the maize growths. The best combination in increasing plant height and leaves number was the combination of flat slope and fertilizer level of 100 kg ha-1. The slope and NPK compound fertilization can increase the maize yields. The best combination in accelerating the age of male and female maize flowering, increasing the grain yield was the combination of flat slope and fertilizer level of 100 kg ha-1. While on cob weight was combination of hilly slope and fertilizer level of 100 kg ha-1, whereas on the percentage of cob weight to grain yield was a combination of mountainous slope and fertilizer level of 100 kg ha-1. The slope and NPK compound fertilization can increase the RAE percentage, the EFE subsidized and non-subsidized ratio. The best combination of flat slopes and compound NPK fertilization level of 200 kg ha-1 has significantly increase the percentage of RAE, the EFE subsidized and non-subsidized ratio, but relatively equal to the the level of 100 kg ha-1. If farmers will continue to maize cultivating on the sloping land, it was recommended to arrive at hilly land with a fertilizer level of 100 kg
ha-1 only.
REFERENCES
1. Abdurachman, A, et al (2008). Dry land management technologies and strategies supporting national food procurement. Indonesian Agric Res and Dev J, 27, 43-49.
2. Ardiani, N. (2009). Maize supply chain in the area of Indonesia's production centers. Indonesian J Food, 18, 73-85.
3. Anugrah, I. S. (2010). Maize-based agribusiness for rural economic development in Gorontalo Province. Agric Policy Analysis, 8(4), 363-383.
4. Arviandi, R., Rauf, A., and Sitanggang, G. (2015). Evaluation of inceptisol soil chemical in gambir (Uncaria gambir Roxb) core garden in Salak sub district of Pakpak Bharat Regency. J Online Agroekoteknologi, 3(4), 329 - 1334.
5. Achiri DT, MH Mbaatoh, D Njualem (2017). Agronomic and yield parameters of CHC202 maize (Zea mays L) variety influenced by different doses of chemical fertilizer (NPK) in Bali Nyonga, North West Region Cameroon. Asian J Soil Sci and Plant Nut, 2(4), 1-9
6. BWS Sulawesi II (2019). Hydrological data for the Paguyaman watershed in 2006-2018. Indonesia Ministry of Public Works, Gorontalo.
7. BPS (2019). Indonesia in Fugure 2019. Boad of Indonesia Statistical Center, Jakarta.
8. Chien, S. H. (1996). Evalution of Gafsa (Tunisia) and Djebel Onk (Algeria) phosphate rocks and soil testing of phosphate rock for direct application. In: A.E. Johnston and J.K. Syers (Eds.). Nutrient Management for Sustainable Crop Production in Asia, Bali, Indonesia, 9-12 December 1996, pp.175-185.
9. Changere, A., and Lal, R. (1997). Slope position and erosional effects on soil properties and maize production on a Miamian Soil in Central Ohio. J Sust Agric, 11(1), 5-21.
10. Erselia, I., Respatie, D. W., and Rogomulyo, R. (2017). The effect of different combination of NPK fertilizers and organic fertilizers enriched with functional microbes on the growth and yield of maize (Zea mays L.). Vegetalika, 6(4), 28-40.
11. Fadhilah, A. (2013). Local wisdom in forming the local food power of the Molamahu Pulubala Gorontalo community. J Al-Turas, XIX, 23-37.
12. Gumeleng, G. (2003). Minus one test of N, P, and K fertilizers on the growth and yield of maize in Moyag Modayag Bolaang Mongondow Regency. Thesis (unpublished) Department of Soil Sceince, Faculty of Agriculture, Sam Ratulangi University, Manado.
13. Husain, J., Gerke, H. H., and Huttl, R. H. (2002). Infiltration measurements for determining effects of land use change on soil hydraulic properties in Indonesia. In Pagliai, M and Jones, R. (Eds). Sustainable land management for enviromental protection-soil physics approach. Advances in Geocology, 32, 230-236.
14. Husain, J., et al (2004). Conservation-based maize farming models in Gorontalo Province. Research Report on the Agency for Research, Development and Control of Regional Environmental Impacts Gorontalo Province, Gorontalo.
15. Hermawan, M. K., Sofyan, E. T., and Machfud, Y. (2018). Combination of N, P, K fertilizer with granule organic fertilizer (Pog) to increase the p-available and nutrient uptake of maize (Zea mays L.) in typic eutrudept. Indonesian Agrotech J, 3(2), 107-112.
16. Indonesian Soil and Agroclimate Research Centre Team. (1995). Survey and soil resource mapping on semi detailed levels (scales 1 : 50,000) of Paguyaman areas, North Sulawesi for irrigation and sugar cane development. Final report No. 03b/P2SLA/19.04/95.
17. IAARD. (2009). Indonesian Agricultural Research and Development Agency Statistics in 2009. Indonesian Agency of Agricultural Research and Development, Jakarta.
18. Jocom, S. G., Putri, E. I. K., and Hariyoga, H. (2009). The impact of maize-based agropolitant development and community's participation in the province of Gorontalo: A case study of Pohuwato Regency. Forum Pascasarjana, 32(2), 103-116.
19. Kasno, A. (2009). Response of maize plant to phosphorus fertilization on typic distrudepts. J Soil Trop 14:111-118.
20. Kasno, A. (2010). Response of N and P Fertilizing for maize crop in inceptisols. Paper published at Proceedings of the National Seminar on Agricultural Land Resources. Bogor, 30 November - 1 December 2010. Book II: Land Conservation, Fertilization, and Soil Biology. Center for Research and Development of Agricultural Land Resources. Agricultural Research and Development Agency, Ministry of Agriculture, Bogor.
21. Lorenz, G., Bonelli, C. L., Roldan, S., Araya, C., and Rondano, K. (2000). Soil quality change due to land use in a kastanozem-phaeozem soilscape of semiarid Chaco. Mitteilungen der Deustchen Bodenkundlichen Gesselschaft. Band 93.
22. Mackay, A. D. (1984). Ability of chemical extraction procedures to assess the agronomic effectiveness of phosphate rock materials. New Zealand J Agric Res 27:219-230.
23. Minardi, S. (2002). Study on water supply regulation and TSP dosage in influencing the performance of maize (Zea mays L.) in vertisol soil. J Soil Sci Agroclimatol, 2 (1), 35-40.
24. Ma', B. L., Subedi, K. D., and Costa, C. (2003). Comperison of crop based indicator of soil nitrate test for maize nitrogen management. Agron J, 97(2), 462-471
25. Muyassir, Supardi, and Iwan, S. (2012). Changes in physical properties of inceptisols due to different types and doses of organic fertilizers. Lentera, 12(1), 1-8.
26. Mensah, F. B. Y., and Mensah, M. (2016). The effect of phosphorus and nitrogen fertilizers on grain yield, nutrient uptake and use efficiency of two maize (Zea mays L.) varieties under rain fed condition on Haplic Lixisol in the forest-savannah transition zone of Ghana. Environ Syst Res, 5(22), 1-17.
27. Nursyamsi, D., Budiarto, A., and Anggria, I. (2002). Management of nutrient deficiency on inceptisols to improve maize growth. Indonesian Soil and Clim J, 20, 56-68.
28. Nurdin, et al (2009). Response of maize (Zea mays L.) lamuru fm variety with fertilized N, P, and K in North Isimu vertisols of Gorontalo Regency. J Soil Trop, 14(1), 49-56.
29. Niu, J., Zhang, W., Ru, S., Chen, X., Xiao, K., Zhang, X., Assaraf, M., Imas, P., Magen, H., and Zhang, F. (2013). Effects of potassium fertilization on winter wheat under different production practices in the North China Plain. Field Crops Res, 140, 69-76.
30. Nahidan, S., Nourbakhsh, F., and Mosaddeghi, M. R. (2015). Variation of soil microbial biomass C and hydrolytic enzyme activities in a rangeland ecosystem: are slope aspect and position effective? Arch. Agron. Soil Sci. 61(6), 797-811.
31. Ngosong, C., Bongkisheri, V., Tanyi, C. B., Nanganoa, L. T., and Tening, A. S. (2019). Optimizing nitrogen fertilization regimes for sustainable maize (Zea mays L.) production on the volcanic soils of Buea Cameroon. Advance in Agric, 2019, 1-8.
32. Pomalingo, N., and Husain, J. (2003). Impact of land use change on soil hydraulic properties and its spatial variability. In Proceeding National Congress VIII of Inonesian Soil Science Society, Padang, 21-23 Juli 2003, p. 250-256.
33. Rachim, D. A. (2007). Basics of soil genesis. Department of Soil and Land Resources, Faculty of Agriculture, Bogor Agricultural University, Bogor.
34. Sardans, J., Penuelas, J., and Estiarte, M. (2008). Changes in soil enzymes related to C and N cycle and in soil C and N content under prolonged warming and drought in a Mediterranean shrubland. Appl Soil Ecol, 39(2), 223-235.
35. Saeri, M., and Suwono. (2012). Study of effectiveness of fertilizer NPK Pelangi 20:10:10 in efforts to increase maice farmers results and revenue in Tuban upland. Proceeding National Seminar on Food Sovereignty and Energy, June 2012, Faculty of Agriculture, Trunojoyo University, Madura p.1-9.
36. Soil Survey Staff. (2014). Keys to soil taxonomy. 12th Edition. United States Department of Agriculture, Natural Resource Conservation Service, Washington. D.C. USA.
37. Solihin, S., Sudirja, R., and Kamaludin, N. N. (2019). Application of potassium fertilizer in increasing growth and yield of sweet corn (Zea mays L.). J Agrikultura, 30 (2), 40-45.
38. Subandi, M., Hasani, S., and Satriawan, W. (2017). Efficiency of nitrogen and phosphorus fertilizers with the addition of biological fertilizers to maize (Zea mays L.) pertiwi-3 varieties. J Istek 10(10), 206-225.
39. Titah, T., and Purbopuspito, J. (2016). Maize growth response to the provision of NPK, urea, SP-36, and KCl fertilizers. Eugenia, 22(2), 62-69.
40. Wezel, A., Steinmuller, N., and Friederichsen, J. R. (2002). Slope position effects on soil fertility and crop productivity and implications for soil conservation in upland northwest Vietnam. Agriculture, Ecosystems & Environment, 91(1-3), 113-126.
41. Wati, Y., Alibasyah, M. R, and Manfarizah. (2014). The effect of slopes and organic fertilizers on runoff, erosion and yield of potatoes in Atu Lintang Sub-district Aceh Tengah Regency. J Land Res Management 3(6), 496-505.
42. Wijaya, A. A., Lumbanraja, J., and Ginting, Y. C. (2015). Effectiveness of organonitrofos fertilizer test and its combination with inorganic fertilizer on growth, nutrient uptake and production of cucumber (Cucumis sativus L.) plants in the second growing season in the ultisol soil of the Gedung Meneng. J Trop Agrotech, 3(3), 409-421.
43. Xue, R., Yang, Q., Miao, F., Wang, X., and Shen, Y. (2018). Slope aspect influences plant biomass, soil properties and microbial composition in alpine meadow on the Qinghai-Tibetan plateau. J Soil Sci Plant Nutr, 18(1), 1-12.
44. Yasin, M. H. G., Singgih, S., Hamdani, M., and Santoso, S. B. (2007). Biodiversity of maize germplasm. In Hermanto, Suyamto, Sumarno (2007). Maize: production and development techniques. Center for research and development of food crops, Agricultural research and development agency, Indonesian ministry of agriculture, Jakarta.
45. Yunus, F., Abidin, Z., and Xyzquolyna, D. (2018). Analysis of maize farming incomein dryland in Bakti Pulubala District Gorontalo Regency. J Agropolitan, 5(1), 28-37 .
46. Zubachtirodin, F., and Kasim. (2012). The Status of the open pollinated maize varieties on maize farming in Indonesia. Bull Food Crop Sci & Tech 7, 25-31.
47. Zulkarnain, E., Evizal, R., Lumbanraja, J., Rini, M. V., Satgada, C. P., Agustina, W., Amalia, H. R., and Awang, T. H. (2017). Inorganic fertilizer application and organonitrofos sugarcane (Saccharum officinarum L.) in dry land Gedong Meneng. J Penelitian Pertanian Terapan, 17(1), 77-84.
