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crop use withdrawals from the system. This technique allows for minimization of crop stress due to over- or underwatering the crop.


Leaching


In the arid Southwest, salinity manage- ment is another critical factor to consider due to the potential of salt buildup in the soil to the level of negatively impacting crop growth and development. A leaching requirement should always be employed, which is simply a percentage increase in applied irrigation water to effectively man- age salts in the soil profile. This leaching requirement is based upon the salinity of the irrigation water being applied and the salinity of the soil at which less than 100 percent yield potential may be realized, and it is calculated using the following equation:


LR = ECw 5ECe()ECw


In this equation, ECw is the salinity of the irrigation water expressed as deciSiemens per meter {dS/m}, and ECe is the maximum soil salinity tolerated by the crop or the salinity at which point the potential yield drops below 100 percent (or whatever potential yield loss the producer is willing to tolerate). The following equation is employed to then determine the amount of water needed, represented as applied water [AW]:


AW = ETa 1LR


Management of the incredibly precious resource of water in the desert is critical to sustaining the farming operations in the western United States. Using ETa replacement estimates to efficiently operate SDI systems while also effectively managing for salinity is just one technique producers can employ to better manage their irrigation systems. Advances in irrigation technologies and management strategies, along with advances in crop production technologies, will also go a long way in helping to effectively conserve this resource. As producers learn to implement these advances in technology, they will become more effective in producing environmentally and economically sustainable crops.


0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00


1.2 1.0 0.8 0.6 0.4 0.2 0.0


500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 Heat units accumulated after planting [HUAP]


Fi


F gurre 2. CropCrop coeffic e t u rrepresenta v


fficiient currve fo


epresentatiive ph n l g ca g ow he


ccu


henologiical grrowth stagt ges o heat unitsnits accumullated


orr cottotton g ow n he ese d affte


err plant n


grown in th deserrts of A zon a on w th off cottott n bothoth as a ffununction anting [HUAP]


HUAP]


0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00


500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 Heat units accumulated after planting [HUAP]


Figu


gure 3. A tua afft


Actual crop wa e us a ter p antiing HUAP o water use [ET ] a d cumula veatiive cro a an pl nt ng [HUAP] for a repre op ET ETa as a fufunc epresentat etive planting datedate of Apri 10 n tion pril 10 in th n of heat n ts the llo


heat uniits accumula edated ow de ert


ccu eserts o


Elbert R. Norton, PhD, (Randy) is an associate regional extension specialist with the University of Arizona and also serves as the resident director of the Safford Agricultural Center. His focus is primarily centered around improving the efficiency of desert agricultural systems through a


broad research and extension program directed at solving production challenges faced by growers across the state of Arizona.


off Arizonaona


Arriizona along with on of


irrigationtoday.org 17


Crop water use [ETa


] {in./day} Crop coefficient [Kc ]


First square (initiation of fruiting) First bloom First bloom


First square (initiation of fruiting)


Peak bloom Peak bloom Range for crop cut-out (cessation of flowering)


Range for crop cut-out (cessation of flowering)


Cumulative water use {in.}


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