IRRIGATION METHODS
at 1,450 lb/acre. Also, irrigation water use efficiencies (known as IWUEs) of skip-row treatments were significantly lower than the traditional treatment. In addition, the every-row configuration with higher initial installation costs increased average cotton yields by 5.1% and IWUE by 6.7% over the traditional crop row/ SDI lateral configuration. The 30-50 configuration increased yield by 3.0% over traditional.
Based on these results, use of the traditional or 30-50 planting configurations should be delayed until adequate soil water is obtained through irrigation or rainfall. The skip-row or skip-row plus configurations could possibly be used as a last resort late in the planting window.
Testing the hypothesis
Due to its method of water delivery, SDI minimizes irrigation water losses due to evaporation during the preplant and early season periods, resulting in high water storage efficiency particularly important at low irrigation capacity. Experiments were conducted to test this hypothesis using different SDI installation designs and irrigation capacities in adjacent fields on clay loam soils over four- and five-year periods.
Figure 1. Crop row/SDI lateral configurations in field tests at the Texas A&M AgriLife Research Center, Halfway, Texas, 2013-2018
zone during periods of low rainfall, high temperatures and high wind speeds. During the 2011 Texas drought, after 8 inches of preplant irrigation and well past the optimum cotton planting date, the plan to plant 30-inch spaced crop rows on 60-inch spaced SDI laterals was abandoned. However, single cotton rows were successfully planted directly over SDI laterals in a “skip-row” pattern. Based on this experience and to document methods that might improve crop establishment with SDI, a field experiment having five crop row/SDI lateral configurations, each with two planting dates, was conducted over six consecutive years to determine differences in plant stands, cotton yields, cotton fiber qualities and water productivities (see fig. 1).
Averaged over planting dates and years, the early planted, skip-row and skip-row plus yields at 1,250 and 1,430 lb/acre, respectively, were less than the late planted, traditional treatment
12 Irrigation TODAY | Fall 2020
Treatments included different levels of preplant and vegetative period irrigations. In both experiments, under seasonal growing conditions ranging from favorable to unfavorable, yields and crop values were only modestly increased by additional preplant irrigations above that required for germination. Among treatments with common preplant amounts, larger irrigation amounts during the vegetative period did not significantly increase yield or crop value in any individual year or any group of years. In growing season groupings, having unfavorable to favorable weather conditions, as seasonal irrigation increased, gross irrigation value decreased. Outcomes were partially attributed to both early season rainfall and weather events that disrupted plant development reducing the value of the “extra” preplant and vegetative irrigation during these years. However, the possibility exists, on heavier soils within the southern High Plains, that SDI productivity can be improved by limiting preplant and early season irrigations under deficit irrigation conditions.
Developments that continue to increase the productivity of SDI systems include improved understanding of the differences in how newer cotton varieties and corn hybrids tolerate water stresses during their growth cycles and the rapid advancement in sensor and communication technologies which can lead to better tools for irrigation management. Research objectives will continue to focus on methods and equipment to elevate both rainfall and irrigation water productivity in water-short environments.
James P. Bordovsky, PE, F. ASABE
irrigationtoday.org
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