CC BY
135
Journal of Stress Physiology & Biochemistry, Vol. 10 No. 2 2014, pp. 144-154 ISSN 1997-0838 Original Text Copyright © 2014 by Vafa, Naseri, Moradi and Jafarian
ORIGINAL ARTICLE
Evaluation of Qualitative and Quantitative Traits of Maize (cv. 604) Under Drought Stress and Plant Density
Parvaneh Vafa*1, Rahim Naseri2, Meysam Moradi3 and Taiebeh Jafarian4
1 Ph.D. student in Crop Ecology, Faculty of Agriculture, Ilam University, Ilam, Iran
2 Young Researchers and Elite Club, Ilam Branch, Islamic Azad University Ilam, Iran
3 Faculty Member, Department of Agriculture, Pyame Noor University. PO.BOX 19395-4697. Tehran.
I.R. Iran.
4 Ph.D. student in Crop Physiology, Faculty of Agriculture, Ilam University, Ilam, Iran *E-Mail: parisa_vafa2006@yahoo.com
Received January 9, 2014
In order to study the effects of drought stress and plant density on yield and yields Components of maize (cv. 604), an experiment was conducted as a split plot based on randomized complete block design with four replications in Ilam station, Iran during 2007-2008 growing season. The treatment were three levels of irrigation (90, 120 and 150 evaporation (mm) from pan (Class A)) as main plots, four planting densities (90000, 100000, 110000 and 125000 plants ha-1) as sub plot. The results showed that different levels of irrigation on the most of measured traits were significant at 1% probability level. Level of irrigation 90 mm evaporation (mm) from pan had a highest a number grain per row, 1000 kernel weight, grain yield and biologic yield other than traits. Between plating density the most of measured traits were significant. The highest grain yield, row per ear, number grain per row, biologic yield and harvest index obtained in 110000 plants ha-1. Interaction effect of irrigation x plant density was effect on grain yield. The highest grain yield from 90 mm evaporationx110000 plants ha-1 and the lowest grain yield from 150 mm evaporationx90000 plants ha-1.
Key words: Drought stress, Planting density, Grain yield, Yield components, Zea mays L.
ORIGINAL ARTICLE
Evaluation of Qualitative and Quantitative Traits of Maize (cv. 604) Under Drought Stress and Plant Density
Parvaneh Vafa*1, Rahim Naseri2, Meysam Moradi3 and Taiebeh Jafarian4
1 Ph.D. student in Crop Ecology, Faculty of Agriculture, Ilam University, Ilam, Iran
2 Young Researchers and Elite Club, Ilam Branch, Islamic Azad University Ilam, Iran
3 Faculty Member, Department of Agriculture, Pyame Noor University. PO.BOX 19395-4697. Tehran. I.R. Iran.
4 Ph.D. student in Crop Physiology, Faculty of Agriculture, Ilam University, Ilam, Iran *E-Mail: parisa_vafa2006@yahoo.com
Received January 9, 2014
In order to study the effects of drought stress and plant density on yield and yields Components of maize (cv. 604), an experiment was conducted as a split plot based on randomized complete block design with four replications in Ilam station, Iran during 2007-2008 growing season. The treatment were three levels of irrigation (90, 120 and 150 evaporation (mm) from pan (Class A)) as main plots, four planting densities (90000, 100000, 110000 and 125000 plants ha-1) as sub plot. The results showed that different levels of irrigation on the most of measured traits were significant at 1% probability level. Level of irrigation 90 mm evaporation (mm) from pan had a highest a number grain per row, 1000 kernel weight, grain yield and biologic yield other than traits. Between plating density the most of measured traits were significant. The highest grain yield, row per ear, number grain per row, biologic yield and harvest index obtained in 110000 plants ha-1. Interaction effect of irrigation x plant density was effect on grain yield. The highest grain yield from 90 mm evaporationx110000 plants ha-1 and the lowest grain yield from 150 mm evaporationx90000 plants ha-1.
Key words: Drought stress, Planting density, Grain yield, Yield components, Zea mays L.
Maize is one of the most important crops which have a great importance in human nutrition, animal rising, poultry feeding, and industry in recent years many efforts have been made to increase the acreage under cultivation in order to reduce the annual imports of corn and many research have been implemented in various fields related to corn (Kafi Ghasemiand Esfahani, 2005). The most
important factor limiting crop production in the world is drought stress (Bashandi and Poehlman, 1974). Iran is placed in arid and semi-arid climate and water shortage is one of the basic problems of agriculture in Iran. Therefore, the occurrence of water stress during plant growth is inevitable. The reaction of different crops and different types of the same plant to drought stress is different (Vieira
et al., 1991). According to the estimates made by Levitt (1980), perhaps only ten percent of the arable lands in the world are categorized as lands free of stress. The drought stress is one of the main stresses which allocate 26 % of the whole stresses to it. Lots of stresses affect plants often directly and indirectly through drought stress. Generally drought affects all aspects of the growth of plants and also most of its physiological aspects (Hung, 2002).
Water shortage influences the opening and closing of stomata due to cell swellings, accordingly the processes of photosynthesis, respiration and transpiration are affected. On the other way, it negatively affects plant growth by effecting enzymatic processes which are directly controlled by water potential (Mansouri-Far et al., 2005). Drought stress affects morphological, physiological and biochemical aspects of plant growth through anatomical changes (Emam and Ranjbar, 1999).
Monneveux et al. (2006) reported that the main limiting factor in the development and production of maize is seasonal drought. Timl et al. (2001) stated that the aggregation process in maize is determined by photosynthesis in maize leaves, the amount of sugars, starch, acid and cytokines. Water shortage and existence of shade in an interval of five days before pollination reduces grain in ending parts of the maize. Water stress during pollination of maize causes a small number of eggs fertilizing, or even it is possible not to fertilize at all, it also can cause abortion, accordingly fewer number of maize grain is produced (Banziger et al., 1999; Pervez et al., 2004). Water shortage reduces the amount of storage in plants stem through reducing photosynthetic capacity; accordingly grain weight reduces (Campos et al., 2004; Echarte et al., 2006). Water stress during or before pollination reduces the number of grains, while water stress after
pollination reduces grain weight (Banziger et al., 2002). The performance of dry matter is the
consequence of plant community regarding its use of solar radiation during the growing season. Plant community needs sufficient leaf surface to be
distributed evenly covering the earth surface
completely. This purpose can be achieved by
varying the density of plants and its distribution of plants n ground surface. Shibles et al. (1996) reported that in the condition in which the row spacing was 76 cm, the yield performance was 1.5 % more than the condition in which row spaces was 102 cm. They also showed that in the condition in which row spaces was 51 cm, the yield was 3.5 % more. Farnham (2001) reported that with varying the row spaces from 76 cm to 38 cm, the yield performance of maize reduces. Cox and Cherney
(2001) stated that the yield performance of dry matter and also the amunt of yield in the primary stages of planting maize is more when the row spacing is 38 cm, compared to the condition in which row spacing was 76 cm. in a two-year study, Banaei et al. (2004) showed that there was a significant difference in an agricultural land with this conditions : the single cross being equal to 704, maize being planted in double rows with 20 cm space between them, density of eighty thousand plants per hectare, an average yield of 15.22 tons per hectare, compared to the lands with less or more densities being planted in one row. Ottman and Welch (1989) found that by getting rows wider, the share of radiation absorption became less for the leaves placed in lower part compared to those leaves which are placed in narrow rows. In this experiment, the difference between row spacing of 114 cm and a row spacing of 38 to 76 cm in radiation absorption was clear. When the row
spacing was increased to 152 cm, this difference was clearer.
The amount of radiation absorption and the total energy absorbed by the plant is more in lands in which the row spacing is less. Aside from this, the air entry and its exit will improve, the evaporation rate will reduce, and water use efficiency will increase in narrower rows (Fagerria, 1992). Ferreira and Abreu (2001) also stated that by increasing plant density, the yield will increase. Because when the density is lower, the amount of radiation absorption and dry matter production is less. This decline was due to lower leaf surfaces. Amanulla and Ghnlam (1990) stated that by increasing the density of plants to 80 plants per square meter, the number of pods per plant will decrease. Bahrani and Babaei (2007) stated that by increasing plant density, it will be added to yield, but when density is too high, the yield index will decrease.
The reason for this is the increase in shading and competition between shrubs which result in reduction in radiation absorption by plants. Compared to the lands in which the density is lower, less photosynthesis material is allocated to the grain. The purpose of this experiment is to investigate the effect of the interaction between drought and density of plants on the yield and its components.
MATERIALS AND METHODS
In order to study the effects of drought stress and plant density on yield and yields Components of maize (cv. 604), an experiment was conducted as a split plot based on a randomized complete block design with four replications in Ilam station, Iran during 2007-2008 growing season. The treatment were three levels of irrigation (90, 120 and 150 evaporation (mm) from pan (Class A)) as main plots,
four planting densities (90000, 100000, 110000 and 125000 plants ha-1) as sub plot. The region was placed in 33 degrees latitude, 7 minutes north and 46 degrees longitude, 10 minutes east, the altitude from sea surface was 155. A deep plowing and two perpendicular disks were conducted to prepare a proper condition for planting grains. After spraying and fertilizing operations, another disc was conducted to mix fertilizer and pesticides with soil. Then the leveling operation was conducted. The seeds used in this experiment were Hybrid 604. The rate of precipitation and physical and chemical properties of soil are shown in Table 1&2.
The seeds were disinfected with Vitavax fungicides before planting. When planting, at first 3-5 cm deep furrows were created on each row, to ensure that seeds will grow, 2 seeds were planted in each furrow. After the growing of seeds, the thinning operation of leaves was conducted. In order to supply the fertilizer needed by plants, ammonium phosphate and urea fertilizers were used. 80 kg ha-1 of ammonium phosphate were used that all of it was used in the beginning process. 200 kg ha-1 of urea was used. Half of the used urea was used in the beginning process and the other half was allocated to the plant in the stage that the stem was growing. After the removal of two adjacent rows and 0.5 m from the beginning and end of each line as a marginal effect, 10 plants were selected randomly from the middle of the row. After harvesting, a note was taken from the number of row grains per ear, number of grains in row, and thousand grain weights. Data analysis was conducted by MSTAT-c software. The means of the traits were compared by Duncan's multiple range tests.
RESULTS AND DISCUSSION
Grain Yield
The results of the analysis of variance of grain yield are presented in Table 3. A significant difference was observed between different levels of irrigation. The most and the least grain yield belongs to the irrigations with 90 mm and 150 mm evaporation respectively (Table 4). We can connect the reduction in grain yield to the effects of water shortage. Water shortage causes accelerating plant aging and reducing the grain filling period. We can also make a connection between the grain reductions, the signals sent from roots to leaves regarding stomata closure and also reduction of photosynthesis (Brevedan and Egli, 2003). The grain yield had a significant difference in various plant densities in the condition in which the water stress had 150 mm evaporation compared to other irrigations with 90 mm and 12o mm evaporations. With increasing water stress, grain yield decreased in all various plant densities. The amount of reduction was less in two levels of irrigation with 90 and 120 evaporation, compared to the third level of irrigation with 150 mm evaporation in which the amount of reduction was so high. These results were consistent with Larson and Clegg (1999) study. Tolk et al. (1998) conducted a study about the effect of different soil types and different levels of irrigation on maize, they concluded that a reduction will occur in grain yield when the available water limits in lower levels. Generally all traits showed a negative reaction to water stress and water stress had the highest effect on grain yield. This reduction in grain yield occurs due to a sharp decrease in the number of grains per row, ear length and 1000 grain weight. This is due to water stress in flowering and grain filling stage. Gomes-Sanchez et al. (2000), in their studies concluded that water stress in
developing stage of the plant can cause reduction in the amount of leaf surface, which may lead to a decrease in grain yield. The analysis of the interactions between the variables show that the highest grain yield belongs to the condition in which irrigation has 90 mm evaporation and plant density is 110000 plants ha-1. And the lowest grain yield belongs to the condition in which irrigation has 150 mm evaporation and the plant density is 90000 plants ha-1.
Number of Row Grains per Ear
The results of the study showed that the difference existing between different levels of irrigation causes a significantly difference in the number of kernel in maize (Table 3). The comparison of means of the number of row grains per ear in different levels of irrigation shows that the maximum and minimum number of row grains per ear was devoted to 90 mm and 150 mm evaporations respectively. The number of row grains per ear did not differ significantly between 120 mm and 150 mm evaporation treatments (Table 4). The overlap between pollen and pollen reception of silk is not possible in the condition of drought stress. So the maize's ovaries will fertilize partially. The fact that the female flowers do not inoculate results in forming irregular rows per ear. These results were consistent with the findings of Andrade et al. (2002). The effect of plant density on number of kernel rows per ear was not significant (Table 3). However, the maximum number of kernel rows per ear was observed in 110000 plants ha-1 and the minimum number of kernel rows per ear was observed in 90000 plant densities per hectare (Table 4). The analysis of the interaction between these two variables showed that the maximum number of kernel per ear belongs to 60 mm evaporation with 110000 plants ha-1, and the
minimum number f grain per ear belongs to the condition with 150 mm evaporation and 90000 plants ha-1 (Table 5).
Number of Grains in Row
The results of the analysis of variances related grain number in rows is presented in Table 3. There was a significant difference on the number of grains in row regarding different levels of irrigation (Table 3). As the Table shows, the maximum and minimum number of grains in row belongs to the irrigations with 90 mm and 150 mm evaporations respectively (Table 4). There was a significant difference between different treatments of irrigations with 90 mm and 120 mm evaporation regarding the mentioned variable. Since water stress decreases the transfer of nutrients from leaves and other parts of the plant to seeds, drought stress also leads to soon reaching of seeds. Besides reducing the amount of photosynthesis, this reaction causes a decline in grain yield. The number of grains per row which is a genetic trait of different types of seeds is so sensitive to drought stress. Among the reasons for the occurrence of this difference is that water stress can cause changes in the appearance of tassels. So when tassels appear, the pollination has been done and there is not any live pollen to inoculate female flowers or its amount has declined much. So most of the eggs do not fertilize and therefore they will not form seed and less number of grains per ear will form. Another reason for this is that the fetus of some eggs that have been fertilized will be aborted in this stage due to drought stress or increasing irrigation intervals. So fewer grains will be formed, therefore there will be fewer grain in per row and in the maize. These findings are consistent with Echarte et al. (2004) findings. Monneveux et al. (2006) stated that the decline in the number of grains per ear has a
greater effect on the decrease in the grain yield in comparison with 1000 grain weights effect on grain yield. The effect of different planting arrangements on the number of grains per ear was significant (Table 3). The maximum and minimum number of grains per ear belongs to 110000 and 90000 plant plants ha-1, respectively (Table 4). The analysis of the interactions between irrigation and plant densities showed that the highest number of grain per ear belongs to the situation in which the amount of evaporation is 60 mm and plant density is equal to 110000 plants ha-1, and the lowest number of grains per ear belongs to the situation with 150 mm evaporation and 90000 plants ha-1 (Table 5).
1000-Grain Weight
Based on the results, the effect of different irrigation levels on 1000-grain weight were significant at one percent level (Table 3). The maximum and minimum 1000-grain weights, was allocated to 90 mm and 150 mm evaporation respectively, (Table 4). 1000-grain weight depends on photosynthesis materials and remobilization of stored materials. Also the speed of grain filling is a determining factor in 1000-grain weight. The decrease in transfer of supply to seeds can lead to reduction in grain weight. Of course, reduction in the speed of material transfer and reduction in grain filling period can exacerbate the decline. During drought stress at the end of pollination, the effect of lack of moisture is more evident on 1000-grain weight. Campos et al. (2004) and Echarte et al. (2006) showed that drought stress reduces the amount of material storage by reducing photosynthetic capacity in maize. Finally grain loses weight. Banziger et al. (2002) in their experiment stated that grains will wrinkle due to water stress in milky stages, therefore the final weight reduces. It
seems that drought stress in this stage causes a reduction in photosynthesis materials. Therefore the leaf surface will reduce and less dry materials will be produced. It leads to grain wrinkling and a loss in grain weight. The finding of this study is consistent with findings of Recap Akir (2004) and Echarte et al. (2006). Based on the results, we can say that the effect of different planting arrangements on 1000-grain weight is significant at one percent level of probability (Table 3). The maximum 1000-grain weight belonged to 125000 plants ha-1 which was significantly different from other densities (Table 4). The results of the interactions between these two traits show that the highest effect of irrigation and plant density belongs to the situation in which evaporation is equal to 90 mm and plant density is 125000 plants ha-1, and the minimum 1000-grain weight is in the condition with 150 mm evaporation and 90000 plants ha-1 (Table 5).
Biological Yield
The effect of different levels of irrigation on biological yield got significant (Table 3). As the Table of the averages of biological yield in three different levels of irrigation shows, the maximum and minimum amount of biological yield belongs respectively to the irrigations with 90 mm and 150 mm evaporations (Table 4). The reduction occurred in biological yield was due to reduction in dry matter accumulation. Since the speed of accumulation of dry materials is still too much in the vegetative phase, reduction in the amount of irrigation will causes a sharp damage to dry materials; eventually biological yields will be affected. If irrigation reduction occurs in the final stages of the development of plant, the amount of damage will be less. Cosculleola and Fact (1992) observed that the increase in the amount of
drought stress will cause a high reduction in the amount of the potential water of leaves; therefore dry material yield will reduce. Ourcut and Nilsen (2000) believe that the reduction in dry materials' weight due to drought stress leads to leaf surface reduction which leads to reduction in the amount of light absorption and photosynthesis. Iramki et al. (2000) stated that leaves' high temperature due to closure of stomata under drought stress is one of the major causes of reduction in dry matter production in plants. The comparison of biological yield showed that the highest and lowest biological yield belongs to 110000 and 90000 plants ha-1 respectively. In lower densities, the amount of radiation absorption is lower, so the coefficient of photosynthetic efficiency is less in lower densities. On the other hand, in higher densities with a higher leaf surface index is, enough solar radiation will be absorbed but photosynthetic efficiency is very low due to mutual shading of leaves. Therefore, the maximum absorption of light in a longer period of vegetation growing season is very important. The analysis of the interaction between different levels of irrigation and plant density shows that the highest biological yield belongs to the situation with irrigation with 90 mm evaporation and 110000 plants ha-1, also the lowest amount of biological yield belongs to 150 mm evaporation and 90000 plants ha-1 (Table 5).
Harvest Index
The analysis of variances showed that the effect of different levels of irrigation on harvest index was statistically significant (Table 3). The comparison of the means of harvest index showed that the maximum and minimum amount of harvest belongs to 90 mm and 150 mm evaporations respectively (Table 4). The results show that increasing irrigation intervals leas to a decrease in dry material yield and
grain yield, so the harvest index does not differ so much. These findings are consistent with Sinclair et al. (1990) investigations. Cox and Julliof (1986) conducted an investigation on soybeans and sunflower in terms of lack of soil moisture, they observed a reduction in dry matter yield and harvest index in both species under drought stress and this reduction was greater in soybean. The results of data analysis showed that the effect of different planting densities were significant at the
1% level (Table 3). The highest harvest index belongs to 110000 plants per hectare and the lowest harvest index belongs to 90000 plants per hectare density (Table 4). The analysis of the interaction between irrigation and plant density shows that the highest harvest index belongs to 90 mm evaporation and 110000 plants ha-1, and the lowest harvest index belongs to 150 mm evaporation and 90000 plants ha-1 (Table 5).
Table 1: Monthly mean value of precipitation and relative humidity in Ilam station, Iran in 2007-2008 growing season
Month Min temp (C) Max temp (ü) Pmm)3^^ Min- RH (%) Max. RH (%)
Oct 18.1 36.9 0.4 14 46
Nov. 15.4 27.5 21.0 34 70
Dec. 8.9 19.5 24.6 48 88
Jan. 9.7 20.9 15.7 40 80
Feb. 8.6 20.2 31.7 34 78
Mar. 14.1 26.0 27.2 25 62
Apr. 15.2 29.1 34.0 20 61
May 21.5 35.0 22.7 14 47
Jun. 27.1 44.0 0.0 7 23
Jul. 29.5 45.7 0.0 8 23
Aug. 30.5 46.7 0.0 9 23
Sep. 25.3 42.7 0.0 7 21
Table 2: Physical and chemical properties of soil
Soil texture EC (ds.m-1) pH O.C (%) N (%) P (mg.kg-1) K(mg.kg-1)
Sandy loam 0.71 7.3 1.28 1.12 5.4 280
Table 3. Analysis of variance for yield, yield components, harvest index and biological yield
s.o.v df Grain yield number of row grains per ear number of grains in row 1000-grain . ... . ,, Biologic yield yield Harves t index
Replicatio n 3 5312.500 0.99 2.1 2.2 14132727.91 0.91
Irrigation 2 41212623.9 ** 7.1** 312.7** 593.6** 117680692.8** 29.4**
Error 6 5955.9 0.12 0.59 16.3 101056.6 0.8
Plant density 3 823869.6** 0.13 ns 16.5** 591.6** 1164808.4** 21.8**
IxP 6 538164.4** 0.86** 9. 3 * 581.2** 5916966.1** 70.1**
Error 27 13867.9 0.031 0.4 19.1 159061.3 0.8
c.v (%) 12.6 9.1 7.8 8.2 13.2 7.6
ns: Non-significant *and **: Significant at 5% and 1% probability levels, respectively
Table 4. Mean comparisons of yield, yield components, harvest index and biologic yield
Main effects Grain yield (kg. ha-1) number of row grains per ear number of grains in row 1000-grain weight (g) Biologic yield (kg ha-1) Harvest index (%)
Irrigation (mm)
90 7650a 15.7a 42.1a 315.1a 16075a 47.5a
120 6415b 14.1b 39.5a 305.6b 14110b 45.4b
150 4431c 13.6b 33.3b 303.3b 9741c 45.4b
Plant density
(plants ha-1)
90000 5817c 14.6a 36.3c 312.4a 13070ab 45.17b
100000 6124bc 14.1a 38.9b 310.9b 13100ab 47.75a
110000 6538a 14.7a 41.6a 305.8c 13670a 48.50a
125000 6226b 13.8a 37.8b 304c 1390a 45.75b
Means in each column followed by similar letter(s) are not significantly different using Duncan's Multiple Range Test
Table 5. Mean comparisons of interaction effect for drought stress and plant density on yield, yield components, harvest index and biologic yield
interaction effect Grain yield (kg ha-1) number of row grains per ear number of grains in row 1000-grain weight (g) Biologic yield (kg ha-1) Harvest index (%)
90000 7530b 15.9b 39.7b 311bc 17430a 43.4fg
90mm 100000 7266c 15.3c 40.3b 366.cd 15520c 45.7de
110000 7830a 16.2a 42.3a 318.9a 145200e 53.8a
125000 7081d 15.4c 41.72a 312.5abc 16540b 42.3g
90000 5819g 14.6ef 37.50c 315.5ab 12760g 45.4de
120mm 100000 6561f 15.1c 38.10b 281.1g 13107fg 50.1b
110000 7019d 14.3g 47.60a 297.4e 15210d 45.3de
125000 6772e 14.5fg 39.6b 316.9ab 13380f 50.4b
90000 4397ij 14.2g 33.2e 289.7f 9308i 46.8cd
150mm 100000 4265j 14.5de 33.5d 303.3de 8880i 47.8c
110000 4613h 14.4def 32.63de 301.3de 10550h 43.4ef
125000 4231hi 14.6d 31.5f 312.6abc 10150h 44.3ef
Means in each column followed by similar letter(s) are not significantly different using Duncan's Multiple Range Test
CONCLUSION
The findings of the study showed that drought stress have a significant effect on grain yield, number of grain per ear, number of grain per maize, 1000 grain yield, biological yield and harvest index. The irrigation with 90 mm evaporation allocated the highest amount of yield and yield components to itself and the lowest yield and yield components belong to 150 mm evaporation. Among different plant densities, the density with 110000 plants ha-1 has allocated the highest grain yield to itself due to
its higher row number and also its higher number of grains in rows.
REFERENCES
Banziger, M., Edmeades, G.O. and Lafitte H.R.
(1999). Selection for drought tolerance increases maize yields over a range of N levels. J. Crop Sci. 39: 1035-1040.
Banziger, M., Edmeades, G.O. and Lafitte, H.R.
(2002). Physiological mechanisms contributing to the increased N stress to lerance of tropical maize selected for drought tolerance. Field
Crop Res. 75: 223-233.
Bashandi, M. M., and Poehlman, J.M., (1974). Photoperiod response in mungbean (vihna radiate L.). Euphytica., 23: 691- 697.
Brevedan, R.E. and Egli, D.B. (2003). Short periods of water stress during seed filling, leaf senescence, and yield of soybean. J. Crop Sci., 43: 2083-2088.
Campos, H., Cooper, M., Habben, J.E., Edmeades, G.O. and Schussle, J.R. (2004). Improving drought tolerance in maize view from industry. Field Crop Res. 90: 19-34.
Cosculleola, F. and Fact, J. M. (1992). Determination of the maize (Zea mays L.) yield functions in respect to water using a line source sprinkler. Field Crops Abst. 93: 5611.
Cox, W. J. and Cherney, J. R. (2001). Row spacing, plant density, and nitrogen effects on corn silage. Agron. J. 93: 597-602.
Cox, W. J. and Julliof, G.D. (1986). Growth and yield of sunflower and soybean under water deficit. Agron. J. 78: 226-230.
Echarte, L., Andrade, F.H., Vage, C.R.C. and Tollenaar, M. (2004). Kernel number determination in Argentinean maize hybrids released between 1965 and 1993. J. Crop Sci. 44: 1654-1661.
Echarte, L., Andrade, F.H., Sadras, V.O. and Abbate, P. (2006). Kernel weight and its response to source manipulations during grain filling in argentinean maize hybrids released in different decades. Field Crop Res. 96: 307-312.
Emam, E., and Ranjbar, G. (1999). The effect of plant density and water stress during vegetative phase on grain yield, yield components and water effeciency of maize. Ir. J. Crop Sci. 2(3): 51-62.
Fagerria, W. K., (1992). Maximizing crop yield. Mucle Dekker, Inc.
Farnham, D.E. (2001). Row soacing, plant density, and hybrid effects on corn grain yield and moisture. Agron. J. 93: 1049 - 1053.
Ferreira, A.M. and Abreu, F.G. (2001). Description of development, light interception and growth of sufflower at two sowing dates and two densities. Portugal. Elsevier Sci. 369-383.
Gomes-Sanchez, D., Vannozzi., G.P., Baldini., M., Tahamasebi-Enferadi, S., and Dellvedove., G.
(2000). Effects of soil water availability in sunflower lines derived from interspecific crosses. It. J. of Agron. 371-387.
Hung, B., (2002). Role of root morphological and physiology characteristics in drought resistant of plant. Plant Environ. Intr. 39-64.
Iramki, S.D., Haman, D.Z. and Bastug, R. (2000). Determination of crop water stress index for irrigation timing and yield estimation of corn. Agron. J. 92: 1221-1234.
Kafi Ghasemi, A., and Esfahani, M. (2005). Effects of nitrogen fertilizer levels on yield and yield components of dent corn (Zea mays L.) in Guilan. J. Agric. Sci. Natur. Resour. 12(5): 55-62
Larson, E.J., and M.D. Clegg. (1999). Using corn maturity to maintain grain yield in the presence of late -season drought. J. Produc. Agric. 12(3): 400-405.
Levitt, J. (1980). Response of plants to environmental stress. Chilling, freezing, and high temperature stress 2: 26-54.
Mansouri-Far, C., Modarres-Sanavy, S.A.M. and Jalali-Javaran, M. (2005). Effect of drought stress and nitrogen deficit on quality and quantity of soluble proteins in Maize (Zea mays L.) leaf. Iranian, J. Agric. Sci. 36(3): 625-
637.
Monneveux, P., Sanchez, C., Beck, D. and Edmeds, G.E. (2006). Drought tolerance improvement in topical maize source populations: evidence of progress. J. Crop Sci. 46: 180-191.
Ourcut, D. and Nilsen, E.T. (2000). Salinity and drought stress. Physiol. Plant. Str. 177-235.
Ottman, M.J. and Welch, L.F. (1989). Planting patterns and radiation interception, plant nutrient concentration, and yield in corn. Agron. J. 81: 167-174.
Pervez, H.Z., Srinivasan, G., Cordova, H.S. and Sanchez, C. (2004). Grains from improvement for mid-season drought to tolerance in tropical. maize(zea mays L.). Field Crop Res. 89: 135152.
Recap-Akir, C. (2004). Effect of water stress at different development stages on vegetative and reproducative growth of corn. Field Crop
Res. 98: 1-16.
Shibles, R.M., Lovely, W.G. and Thompson, H.E. (1966). For corn soybeans, narrow rows. Iowa Farm Sci. 20: 3-6.
Sinclair, T.R., Bennett, J.M. and Muchow, R.C. (1990). Relative sensitivity of grain yield and biomass accumutiation to drught in field grown maize. J. Crop Sci. 30: 690-693.
Timl, S., Flannigan, A. and Melkonian, J. (2001). Loos of kernel set due to water deficit and shade in maize: carbohydrate subpplies, Abscisic Acid, and cytokinins. J. Crop sci. 41: 1530-1540.
Tolk, J.A., Howell, T.A. and Evett, S.R. (1998). Evapotranspiration and yield of corn growth on three height plains. Agron. J. 4: 447-454.
Vieira, R.D., Teerony, D.M. and Egli, D.B. (1991). Effect of drought stress on soybean seed germination and vigor. J. Seed Technol. 16: 1221.
