Water is an important factor in crop production, and is of a high value in agricultural Engineering. Water shortage is the most restricting factor in irrigated areas. Because of this limitation quality and quality - wise, deficit irrigation research hase a special value in optimization of water use and determination of water depths in irrigation strategy. Due to The aforementioned, a research project in 1996, in the SWRI(Karaj Station), on sugarbeet, with different levels of water use, was conducted and the yield and
cost functions as well as price equation were obtained.
Optimum depth of water use for sugarbeet was determined based on net
benefit optimization model. Both functions, yield yew) and cost C(w), are a second order function of water use depth. Two equations B(w)=PcXy(w) and N.B(w)=Pcy(w) have been used to estimate the gross and net income, respectively. Some results of this research are as follows:
- Full irrigation (F.I) had the highest yield (59.1 t/hd) but due to cost
increasing and Pol reduction, (and subsequently reduction of price), the final net income decreased (Wm).
- 21 % deficit of water use, had the highest ratio of .!!.. and the maximum net
C
benefit per hectare, but it did not result in the highest net income per unit of
. water use (Ww).
- 34% deficit of water use, had maximum net income per unit of water use. furthermore, it lead to obtain the highest net income in case of possibility of increasing crop area by the amount of water saved from deficit irrigation. This depth is called equal depth of full irrigation, when land is limiting, (WeL).
- 51 % deficit of water use, lead to a net income per unit of water use equal to
net income with full irrigation. This depth is called equal depth of full irrigation when water is limiting (Wew).
- 62% deficit of water use, lead to a gross mcome equal to production cost(Wk).
This research was carried out in RCBD using six irrigation treatments each with three replicates. Irrigation interval, planting and growth conditions were the same for all treatments. In this research, the optimum level of water use from an economic point of view has been calculated to be 115.76 em. In this case the yield of sugar has been amounted to about 7 t/ha.
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