Submitted to: National Conservation Tillage Cotton and Rice Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2006
Publication Date: 1/29/2007
Citation: Baumhardt, R.L. 2007. Adapting the dryland wheat-sorghum fallow rotation for use with dryland and deficit irrigated cotton. 10th Annual National Conservation Systems Cotton and Rice Conference, January 29-30, 2007, Houston, Texas. p. 5-7. Interpretive Summary: The declining Ogallala Aquifer supplies irrigation water for the southern Great Plains. Because of low well yields, many Texas High Plains producers can not irrigate enough to meet the higher water needs of corn. A wheat-sorghum-fallow (WSF) rotation saves rain for dryland crops and may work for irrigated crops. Our objectives were to adapt the WSF rotation for use with cotton under limited irrigation, and measure residue effects on water savings and crop growth. All phases of a wheat-cotton-fallow rotation were started on a Pullman soil in 2004. Wheat was uniformly cropped, harvested, and residues fallowed for 11 months with disk, sweep, and no –tillage. After wheat fallow, cotton was planted in 30 in. rows at 60,000 seed/acre. Soil active and contact herbicides controlled weeds. Cotton was irrigated using a linear move overhead sprinkler. We applied 1 or 2 in. every 10 d to supplement rain and soil water. Fallow storage of rain as soil water increased as crop residues increased. Plant emergence was better with sweep tillage that improved seed soil contact and limited soil water evaporation. Water use increased with more irrigation; but, no and sweep tillage benefitted water use at the low irrigation level. Cotton yields were greatest with no-tillage and then sweep tillage. Yield of no-tillage cotton irrigated with 1 in. every 10 d exceeded yields of disk till cotton irrigated at double that rate. No-till stored more soil water during fallow, had less evaporation after irrigation, and increased cotton water use.
Technical Abstract: Irrigation water in the Southern Great Plains is supplied by the declining Ogallala Aquifer. Because of the decreased well yields, many Texas High Plains producers cannot apply sufficient irrigation water to meet the higher water needs of corn (Zea mays L.) and are growing cotton (Gossypium hirsutum L.). Sorghum [Sorghum bicolor (L.) Moench] grown in rotation with wheat (Triticum aestivum L.) is a successful crop sequence that efficiently uses the spring and summer rain and may be adapted for irrigated crops. The objectives were to adapt cotton and wheat to a limited irrigation cropping sequence with fallow periods, and quantify the effect of residue management practices on crop growth and water conservation. All phases of a wheat-cotton-fallow (WCF) cropping system were installed in 2004 on a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) irrigated with a linear move mid-elevation spray system. Wheat was uniformly cropped, harvested, and residues fallowed for ~11 months using disk, sweep, and no –tillage. After wheat fallow, cotton was planted in 0.76 m rows at 24 seed/m2 in mid-May. Soil active and contact herbicides provided weed control. Cotton was irrigated at 2.5 or 5.0 mm/d on ~ 10 d intervals to supplement rain and soil water. Fallow storage of rain as soil water increased with increasing crop residues, but plant establishment was better with sweep tillage that improved seed soil contact with limited evaporative soil water losses. Cumulative water use increased with increasing irrigation; however, tillage effects were significant only for 2.5 mm/d irrigation. Cotton yields were greatest with no-tillage then sweep tillage. Yield of no-tillage cotton irrigated at 2.5 mm/d exceeded disk till cotton irrigated at double that rate. Residue retaining tillage practices, like no-till, increased crop water use through increased fallow season soil water storage and reduced evaporative losses of irrigation water.