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10AGRICULTURAL SCIENCES
CALCULATION OF THE IRRIGATION REGIME IN THE DESIGN OF SEWAGE FARMS
Anuarbekov K.
Kazakh National Agrarian University, PhD
Abikenova S.
Kazakh National Agrarian University, PhD
Igenbayev N.
Kazakh National Agrarian University, Master
ABSTRACT
This article discusses the method of exploitation of wastewater irrigation systems (WWIS). Presented WWIS exploitation activities - selection of sites for irrigation with wastewater, tillage in irrigated fields, sowing, planting and harvesting, fertilizer system.
Keywords: wastewater, irrigation system, groundwater, fertilizer system, irrigation norm, salt balance, irrigation regime.
Introduction. Waste water is a complex environment that contains various chemical elements and compounds, which can make significant influence on the composition of the soil, plant and groundwater when irrigating it. Therefore, the irrigation regime in each specific case is determined by taking into account the following circumstances:
The necessity of consideration of constant, equal wastewater inflow during the year, plant needs in water, fertilizer and other ingredients, which come with irrigative water has arisen. Absolutely new conditions are created for crops, that differ from normal systems. Therefore their composition has to be selected in accordance with these conditions.
Taking into account specificity of plant growing on sewage farms, there is necessity of consideration of water consumption regime by plants in stages of its development, in the conditions of its sufficient humidification. [1,2]
During individual critical periods of vegetation, crops can't be fully supplied with an inflow of wastewater. Additional irrigation from natural reservoir - a river, a cistern or groundwater can be used for replenishment of this water deficiency. For example, the critical periods in Jambyl and Shymkent Regions begins from the 15th of July till the 15th of August. Their duration depends on the conditions of the year and usually lasts from 10 to 20 days.
The quantity of additional water , that is required to overcome deficiency of water consumption in these periods can be computed according to the following formula:
Wadd = Ww + QTC (1)
where, Wadd -the quantity of additional water , that is required to overcome deficiency of water consumption in these periods of vegetation, m3;
Ww - necessity of crop in water during the reference critical period, m3 , (accepted in the accordance with water utilization scheme);
Q - average daily wastewater consumption, that comes from the city, villages m3/day;
Tc- duration of the critical period, day.
Such periods in the practice of sewage farm designing can be identified by matching irrigation hydro-modulus of crop in crop rotation (q in l/s on 1 ha.) with hydromodulus of wastewater supply (qw), computed, according to the following formula:
qw = —l/sha (2)
W 80,4-Wo
where, ®0- an area of simultaneous watering, ha
Purifying power of soil should be taken into account when irrigation rate and depth is identified. It is known that during watering and the following movement of wastewater over the surface and over the soil profile intensive cleaning is possible due to mechanical, molecular-sorption, ion-sorption, chemical and biological absorbency of soil. The level of cleaning depends on water supply rate and power of filter layer of soil.
The effect of soil cleaning decreases with a rise of water supply rate. On a widely spread loamy south zone of Kazakhstan intensive cleaning takes place with the irrigation rate up to 600mm, and with the 800mm rate and more the soil won't give cleaning effect.
Certain absorbency is peculiar to each type of soil. The bigger it is, the higher the level of wastewater cleaning. For example, Jambyl and Shymkent and Almaty Regions loamy soils have the high level of absorbency. From 60 to 90% water-soluble salt and from 80 to 98% elements of mineral nutrition are on hold in a metric layer of the soil.
Absorbency of soil decreases to the end of the growing season and in the following years of watering. This can be explained by the fact that soil is saturated through prolonged irrigation with elements that come with wastewater and its cleaning ability decreases over time. Therefore it is very important to keep balance between the inflow of wastewater ingredients and their use by plants; keep irrigation interval.
Water-holding capacity of the soil needs to be taken into account for the proper use of wastewater. Volume of the run-off needs to be close to zero on sewage farms. The volume of water that exceeds waterholding capacity, reaches groundwater. The smaller the watering rate is and the longer the irrigation intervals
are the bigger the difference between wastewater inflow and outflow. The watering rate is needed to be calculated in such a way so that it won't exceed acceptable average daily intensity value of irrigation water infiltration and acceptable depth level of ground water.
Annual irrigation rate should be harmonized with the underground run-off conditions.in order to provide an opportunity to decontaminate and clean wastewater during the infiltration process, and plant need in moisture should be taken into account.
Crop satisfaction by water in growing season and enrichment by necessary nutritious elements in soil in beyond-vegetation season has to form the basis for the all-year cycle of irrigation on sewage farms.
The creation of predominantly descending current, which provides release of salt from upper soil horizons, when the amount of calcium, coming with wastewater and added to the soil in the form of fertilizers is bigger than amount of sodium added to the soil with wastewater, is needed to form the basis of watering.
Irrigation regime of crops should be fixed by taking into account the balance of wetness, water-soluble salt and nutritious elements, that come with wastewater [3,4,5].
Methods. The task of all-year wastewater acquisition on the irrigation fields arises the necessity to use vegetative watering as well as beyond-vegetative watering.
Therefore, annual standards of sewage farm load are summed by the irrigation rates of these seasons of the year. i.e.:
Myear = Mveg + Mb (3)
where, Myear-annual load standard of sewage farm, m3 /ha;
M veg -vegetative irritation rate, m3 /ha;
M b -beyond vegetative irritation rate, m3 /ha;
In order to prevent overload of irrigation fields with wastewater, annual amount of load standards is computed according to the following formula
Mr = qs^T (4)
where, M r -a recommended annual load standard, m3 /ha;
qs -an approximate specific acceptable load standard, m3 /ha;
T -a number of days in the year, day.
The value of the qs is taken according to Instruction design of sewage farms (1976 y.) within 5-30 m3 /ha per day, in accordance with soil and climate conditions.
Vegetative watering is more favorable from the point of its realization conditions. The main task is to provide plants with sufficient water in order to get planned harvest. It is known that water consumption of crops depends on biological peculiarities of plants, climate factors and means of water delivery and water distribution on irrigation fields.
The principles that form the basis for usual irrigation can work as well as for the water regime of the growing season.
A water balance method is more applicable for the calculation of irrigation regime from existing ones, where the calculation parameters of water regime in keeping with good techniques of watering provide good crops and high level of wastewater afterpurification.
The irrigation rate of growing season is computed by the academic A.N. Kostyakov's formula
Mveg =EY-10aP-AW -G, m3 /ha; (5)
where, E -specific water consumption by crops,
m3 /c;
Y -planned yield, c/ha;
a-coefficient of rainfall use;
P -the quantity of rainfall in growing season, mm;
AW-moisture, used by plants from a reserve in soil, m3 /ha;
G -moisture, used by plants from groundwater, m3
/ha;
Beyond-vegetative watering is directed on the creation of the maximum reserve of moisture and accumulation of nutrient elements in soil. Irrigation rate of beyond-vegetative watering is identified as the difference between recommended annual load standards (Ma-) and vegetative rate (Mv), i.e.
Mbw = Ma - Mv, m3 /ha; (6)
In the south of the Republic moisture-loving crops - annual plants, sugar beets, duneraz -use all annual rate in growing season. Therefore in some cases for creation of the reserve of moisture beyond vegetative watering should be carried out with usual water.
The table 1 gives approximate value of irrigation rate of different crops in the south and south-east of Kazakhstan.
Table 1
Approximate value of irrigation rate of different crops in the south and south-east of Kazakhstan
A crop name An annual load standard of Vegetative irrigation Beyond-vegetative irriga-
sewage farms, m3 /ha; rate., m3 /ha; tion rate. m3 /ha;
Zhambyl Region
Sugar beet 5600-5800 200-1200*
Barley 2480-3300 2500-3320*
Winter wheat 5800 2560-3400 2400-3200*
Corn silage 2800-3700 2100-3000*
Perenial grasses 5800-6800 1200*
Almaty Region
Perennial grasses 5000-6000 400-1000
Corn silage 2600-3400 2000-2800
Sugar beet Winter rye 5400 4800-5700 2100-2900 600-1000 2500-3300
Spring grain 2100-2900 2500-3300
Annual plants 3200-4100 1300-2200
Shymkent Region
Corn silage 3100-4300 2700-3800
Lucerne of previ- 7000 6000-7000 1000
ous years 7000 1000
Lucerne of an year
Results. The balance of water-soluble salt in soil is regulated by the establishment of acceptable standards, before emerging signs of weak salinity in soil. i.e.
(7)
- . lOOO Hv(SaccSb) . ,,, .
M =----, (m3/ha)
where, H - an estimated layer of soil, m;
y - volume weight of the estimated layer, t/m3;
Sacc-the value of acceptable concentration of saline solution in soil in % from the weight of dry soil. It depends on the nature of salt and plant and hesitates within 0.3-0.5%.more often 0.3%;
Sb-easily soluble salt content in estimated layer of the salt in the beginning of vegetation in % from weight of dry soil;
K- water soluble salt content in wastewater, g/l.
The formula was drawn up for the worst case, water soluble salt coming with wastewater, fully absorbed in the estimated layer of the soil. Salt removal of soil under the influence of precipitation does not occur, salt removal by plants is not significant and does not affect on salt regime of the soil, the capillary salinity of soil does not occur.
Calculation can give following:
1. At high mineralization of wastewater
Madd<Myear.
Measures on mineralization decrease need to be taken, mixing with clean water more often. Strictly monitor the accumulation of salt in soil. Swilling out is obligatory. Beyond-vegetative watering is carried out only by clean water.
2. At low mineralization of wastewater
Madd>Myear.
How long we could irrigate with wastewater without fear of soil salinization is (more often) identified by a Madd and Myear difference. i.e.
lOOOHviSaccSb) , . .„.
Tsai =-T-rr--, (year) (8)
KMyear J
Salt composition of soil should be checked and swilling out of fields, plastering and other measures directed on salt concentration decrease is carried out (if necessary) after expiration of this date .By the way taking into account that within autumn-winter seasons under the influence of precipitation the process of soil dissolution is ongoing and some amount of salt is dashed out from soil, the acceptable irrigation rate (Myear) which does not cause salinization will be bigger.
Irrigation rate of crops is identified taking into account the dynamics of water consumption of plants and moisture reserve in active layer of soil with such calculation, so that the difficulty does not drop lower that minimum acceptable limit.
Nomogram can be installed in rate calculation of each watering. Academic A.N.Kostykov's formula form the basis of nomogram.
Water reserve in soil decreases before watering to 66-80% in comparison with the minimum moisture-holding capacity MC. The most optimal antecedent threshold in the south is 70% from MC.
The MC value for loamy soil varieties is hesitated within 13-22% from the weight of dry soil.
There is no exception that on the practice the actual irrigation rate will be slight different from estimated one. Therefore it needs to be identified by calculating the actual wetted depth according to the formula
H = m+ml (9)
H1 wo-Y-(pa-po) (9)
where, mi - some deviation from calculated rate, m3/ha;
P - soil moisture corresponding to MC in % from dry soil weight;
00 - soil moisture before watering in % from dry soil weight;
Hi -the actual wetted depth,m; y - volume weight, t/m3.
Irrigation rate is acceptable only when it does not lead to immediate groundwater recharge. And provides high level of soil after purification of waste water.
The optimal value of irrigation rate for the leading crops in the south and south-east of Kazakhstan was identified through the results of lysimetric experiments. The value diversifies within 400-900 m3/ha. While meeting such standards highly-effective cleaning of wastewater will be reached and plants use of elements of mineral nutrition will be higher.
The identification of optimal date of vegetative irrigation plays significant role in soil method of wastewater cleaning. The dates of wastewater irrigation for growing season can be identified as well as for usual irrigation under the conditions that optimal moisture is kept. Our investigations fully confirmed economic expedience of setting a date for another irrigation as it
moves to antecedent moisture of soil within 70% MC. In this case the most optimal is coefficient of water consumption and yield. The threshold decrease of antecedent moisture to 60% MC leads to sharp reduction of yield, whereas increase up to 80% MC leads to unreasonable consumption of irrigation water, that is inappropriate, especially in the regions with insufficient water resources. Moreover, excessive increase of irrigation rate under the conditions of wastewater irrigation increases the load standards on irrigation fields. This, in its turn can lead to the decrease of soil absorbency and pollution of wastewater.
Economical expedience of alternate irrigation conduct when it reaches 70% MC of soil moisture before watering could be monitored on the table 2.
Table 2
The economical indicators if various irrigation regime (using an example of a state farm named after
Indicator Watering with antecedent moisture threshold in % from MC
60 70 80
Harvest of beet-root, c/ha 282 586 628
Sugariness 17,9 14,8 13,8
Provisory sugar yield,c/ha 48,6 87,4 86,4
Total waterconsumption, m3/ha 5763 6640 7097
Coef-t of water consumption,m3/c 20,8 11,4 11,2
Prime cost of beet-root, r/c 1,78 0,97 1,02
Expenses 398 572 635
Rentabiblity,% 87 171 160
Expenses on watering conduct,man/day 1,56 6,3 8,91
Expenses on watering conduct tg/day 116,435 160,93 227,26
The terms of vegetative irrigation is appointed taking into account the biological peculiarities of crops, climate condition, keeping constant water acquisition and distribution on the irrigation fields. The main part of beyond-vegetation irrigation occur in winter season, standard for a watering - from calculation a 1,5-2m of soil layer water-holding capacity.
References
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