Water balance of cotton cropping systems

Date

1997-05

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Publisher

Texas Tech University

Abstract

Cotton (Gossypium hirsutum, L.) is planted on more land area than any other crop on the Texas High Plains. Much of this area is considered highly erodible and must have a conservation compliance plan to participate in government farm programs. Because this region is semiarid, water conservation and efficient water use are important aspects for maximizing cotton lint yields. One popular conservation compliance practice is to plant cotton into a chemically terminated small grain crop that provides wind protection to the growing seedlings. Our hypothesis is that in this semiarid region the use of a small grain cover crop under irrigated conditions could use more water than it conserves compared to conventionally tilled cotton, thus reducing cotton lint yields. This study was conducted during two years and on two soil textures with each soil texture study independent of the other. One was a loamy fine sand (fine-loamy, mixed, thermic, Tortertic Paleustalf) near Brownfield, TX and the other a clay loam (fine, mixed, thermic Tortertic Paleustoll) near New Deal, TX. The main treatments were tillage systems (conventional and conservation using terminated winter wheat residue). The two split plot treatments were water supply based on replacement of calculated potential evapotranspiration (PET). Our results indicated that residue or tillage treatments did not affect the amount of water used by the cotton crop at either location (< 7% difference) except for the 80% ET irrigation treatment at New Deal where the bare soil treatment used 10% more water than the residue treatments for both years. The residue treatment decreased cotton lint yields at both locations (generally > 12% decrease) except for the 50% ET irrigation treatment at Brownfield in 1995 where the residue treatment yielded 14% more cotton lint than the bare soil treatment. The use of terminated wheat residue did not impact the storage of water during any part of the year. During a five-month period associated with wheat growth, the wheat used 20 to 40 mm more water than w as lost through evaporation of soil water at both locations. Our results showed that during this two-year period the use of terminated wheat residue did not benefit the water balance of cotton crops in the southern High Plains, but it did have a negative impact on the cotton yields (usually over a 12% decrease). With these results, we concluded that our hypothesis is correct for the two year study in two locations.

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