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<br />;:.~~,;::;'~~. <br />'.;. ,~' <br /> <br />w <br />......' <br />o <br />o <br /> <br />~~;/t5 <br /> <br />Under individual irrigation summaries, the ETa and precipitation data <br />are shown in the tables' as a value for each irrigation event. The <br />value shown is the calculated ET for the particular crop from the time <br />of previous irrigation event; or for the first irrigation event,it is <br />ETa from the beginning of plant growth to the date of the irrigation <br />event. <br /> <br />The soil moisture deficit before irrigation was determine,d from the. <br />daily water budget computer program AI' sites were probed before <br />the start of the irrigation season to estimate soil moisture deficit <br />before irrigation~ If the infiltrated depth for a particular <br />irrigation event exceeded the soi I moisture deficit before irrigation, <br />then the so i I prof i lei s assumed to be fu II and there is no so i I <br />moisture deficit after irrigation, However, any excess beyond what is <br />needed to fill up the so i I prof i I,e is cons i de red to be deep <br />percolation. <br /> <br />In 1990, the water budget program was updated to more accurately <br />estimate deep percolation for annual crops. In the past, deep <br />percolation for the first irrigation and or pre-irrigation was <br />considered to be any amount that was in excess of that required ~o <br />fill up the first foot of soil; the full root profile was not taken <br />into account. With this method, deep percolation estimate~ were <br />higher than"what they should be. The updated program takes ful I <br />rooting profi Ie into' consideration. All previ.ous data from 1986 to <br />1989 was re-processed using the updated program to ge~ a better <br />estimate of deep perco,lation, soi I moisture and ETa etc. <br /> <br />The seasonal and individual application eff,iciency data shown in Tabl,e <br />2 and individual site summaries IS the ratio of water used <br />beneficially to the total irrigation water applied. The calculation <br />is disc~~sed in Appendix C. <br /> <br />Table 2 and individual site summary tables show that water budget <br />differed greatly for different sites. All sites applied enough ,water <br />to meet crop requirements with the exception of site 18,26 and 51. <br />Most sites over irrigated to cause considerable deep percolation and <br />reduce application efficiency. This is discussed in more detail under <br />irrigation adequacies at sites. <br /> <br />Deep Percolation: In the Grand Valley, deep percolation losses come <br />from on-farm irrigation practices. The seasonal deep percolation <br />losses for the various sites are shown in Table 2 which has been <br />extracted fro'm individual irrigation summaries provided in Appendix D. <br />Also, detailed deep percolation values for each surface irrigated site <br />by irrigation event are provided in Table 3. These are shown in two <br />formats, as acre inches per acre and as a percentage for each <br />individual irrigation event. <br /> <br />14 <br />