Summary of research project: |
Objective and technical fields:
Improvement of water use through optimization of irrigation schedule and nutrient regime as well as determination of cotton water requirements. Development and optimization of water-nutrient regime for cotton, which provides obtaining of high, stable and qualitative yields of raw cotton under efficient water, nutrient and other resources use. Improvement of planning and management of on-farm water use.
Scientific and technical approach:
Increase the efficiency of water, land and other resources use through determination of rational irrigation schedules and nutrient regimes, crop requirements, growth and development of cotton in rocky soils. Importance of the study consists in development of scientifically grounded recommendations on water-nutrient regime for cotton and improvement of on-farm water use management.
Environment characteristics:
Climate of the North Tajikistan is characterized by large daily and seasonal fluctuations in air temperature, intensive solar radiation, dryness of air and low cloudiness. The plot is located at 414 m above sea level and have the following coordinates: latitudes 400 31’ North and longitude 69o 44’ East. Average annual air temperature is 14,1 oC, the coldest period is in January (-2,0 oC), the warmest one is in July ( 29 oC). Duration of a warm period (more than 10 oC) is 220-160 days. Sum of positive temperatures is 2500-4800 oC. Absolute maximum temperature is 34-45 oC, an average one is 30-40 oC. Frost-free period is 100 days at a height of 400-500 m and 140 days at a height of 2000 m. Accordingly, duration of winter period is 50-100 days. Absolute minimum temperature is -27-29 oC. Annual active radiation is 66,3 kk/cm2, at 10 oC - 52,0 kk/cm2. Relative air humidity varies from 23% (in July) to 75% (December). Deficit of air humidity is 1,8 Mb (in December) and 30,8 Mb (in July). Total precipitation is 155 mm, including 53 mm from April till August. Average annual evaporativity is 1725 mm, including 1413 mm from April till September. Average annual wind speed is 2-5 m/sec, quantity of strong wind days is 2-24. There are gray-brown and gray soils in the valley and steppe ones in highlands. Soils of the plot are gray-brown strongly rocky. Top soil (0-30 cm) contains 61,9% of solid sediments out of soil weight, underground layer (30-50 cm) - 74,3%, second half-meter - 71,5%. There are 0,40% of humus, 0,035% of gross nitrogen, 0,112% of gross phosphorus, 8,1 mg per 100g of soil of metabolic potassium in soil horizon. Permeability of strongly rocky soils is 2-3 mm/min, field water capacity is 1600 m3/ha. Volume mass of soil horizon varies from 1,6 to 2,5 g/cm3. In Leninabad province strong rocky soils account for 49701 ha or 24% of irrigated area.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area of the pilot plot is 10 ha (net). Cultivated crop is cotton. Water is supplied through furrows from open earthen network. Efficiency of canals is 0,72-0,85. Canal capacity is 200-300 l/sec. Length of furrow is 100-150 m. Slope of the plot is 0,008.
Methodology:
Field studies and observations of soil moisture and nutrient regime, cotton growth and productivity. The plot was equipped with meters to keep regular observations. In order to study and determine an optimal combination of irrigation schedule and rate of mineral fertilizers, which provides obtaining of high, early ripened and cost-effective yield of row cotton the following irrigation alternatives were compared: waterings under 55-60-60% and 65-70-60% of normal moisture (first figure is «sprouting-flowering», second one - «flowering-fruit formation», third one - «fruit formation-maturity») and under nutrient regimes: N0 P0, N150 P100-200, N250-350 P100-200. For studies systems and combined approach and SoyuzNIKHI (1973) methods were used.
Results:
Soil was fertilized before sowing, during sowing and there were 4 additional feedings according to agro-regulations. Observations showed, that strong winds dried up top soils and by the date of sowing moisture was 30-57% at the depth of seeds location. Therefore, obtaining of even sprouting without initial watering is impossible. The higher level of initial moisture and rate of fertilizers the more waterings and irrigation norms. Thus, differences in quantity of waterings and irrigation norms at expense of fertilizing were the following: 1-2 waterings and 800 m3/ha under 55-60-60 and 65-70-60%, 3-4 waterings and 1400-1600 m3/ha under 75-80-60%. After initial watering, under 55-60-60%, first watering was done on 21st day after sprouting, next waterings before the phase flowering-fruit formation were done in 13-10 days. During the phase flowering-fruit formation irrigation interval was 11-9 days, in irrigation alternative 75-80-60% - 7-5 days. It is identified, that under 55-60-60% waterings are increased from 8 to 9 and the irrigation norm is increased from 4525 to 5507 m3/ha while raising the rate of mineral fertilizers. Difference between gross and net irrigation norm raised, on the average, 1,33-1,36 fold. Depending on initial soil moisture, nutrient regime, slope, permeability and other water-physical characteristics of soil in the pilot plot, water release accounted for 8-19%, underground discharge accounted for 11-20%. According to adopted SoyuzNIKHI methods, evaporation during the watering is taken at 10% for calculating depth of irrigation.
Different irrigation schedules and nutrient regimes influenced considerably on the parameters of cotton growth and development. During the phase flowering-fruit formation (in July 20) there were big differences in area of cotton leaf surface. The last in non-fertilized lot, under 65-70-60%, was 4084 m2/ha, after fertilizing 150 kg of nitrogen and 100 kg of phosphorus per hectare - 15470 m2/ha, i.e. 3,7 times more. An annual rate of nitrogen at 250 kg/ha increases this indicator up to 22762 m2/ha, at 350kg/ha - up to 25530 m2/ha. Raising an initial moisture to 75-80-60% promotes further increase of leaves area, which accounted for 8704, 25911, 28311 and 29936 m2/ha respectively.
Study of total cotton water requirements using methods of water balance showed, that the main income item is irrigation water, which varies depending on water-nutrient regime from 88 to 94,1%. Precipitation is 3,3-5,5%, water extraction from the soil store is 2,6-6,5%. It is identified, that the total cotton water requirements (water discharge for transpiration and evaporation) increases from 5147 to 8556 m3/ha while raising the level of initial soil moisture from 55-60-60 to 75-80-60% and raising the rate of mineral fertilizers from N0 P0 to N250-350 P100-200. Under different water-nutrient regimes the yield of row cotton varies considerably from 1,08 to 3,3 t/ha.
There is relationship between the yield of raw cotton and total crop requirements, which is established. The relationship is curvilinear, expressed by quadratic equation (parabola). Yield of raw cotton increases from 1,0 to 3,3 t/ha while raising total crop requirements from 5,5 to 7,5 Th.m3/ha. Further rise of crop requirements does not lead to substantial changes of the yield. It is proved, that under conditions of gray-brown strongly rocky soils of the North Tadjikistan an optimal irrigation schedule for medium-fiber cotton is watering under 75-80-60% of normal moisture. Rates of fertilizers are varied depending on nutrient content in soils and determined as 250-350 kg/ha of nitrogen, 100-350 kg/ha of phosphorus, 100-150 kg/ha of potassium. Such combination of watering and fertilizers provides 3,3 - 3,6 t/ha of row cotton.
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