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Fluid Journal : Fluid Journal 2005-2007
Winter 2005 Fluid Journal 3 supply available during the growing season. We apply all our in-season N through the water using LEPA or Sub-Surface Drip application sys- tems. We typically apply 30 to 35 lbs N (32-0-0) as a carrier for our preplant application of yellow- herbicide. The remainder of the N Figure 2. Effect of NH4:NO3, applied at varying ratios and water rates, on lint yield of cotton Figure 3. Effect of varying N:P rates, applied at varying water rates, on lint yield of cotton. goes through the water at the rate of 10 to 12 lbs of N/inch of irrigation water (27,300 gallons). Application starts during the squaring stage and continues through the third week of flowering or until August 5 to 10, whichever occurs later. This N management strategy ensures that soil N reserves are low in case September rains occur. Bolls that set in late August to early September have a very low probability of maturing. Recent research has been directed toward the impact of N form. The hypothesis was that a continuous supply of ammoniacal N during the rapid fruit development would reduce the cost of N acquisition and deduc- tion, possibly leaving more of the daily photosynthate for early fruit growth. By fertigating various NH4:NO3 ratios with different water volumes, we were able to determine that a 75NH425NO3 ratio resulted in greater yields per N unit and water (Figure 2). Soil chemistry Soil chemistry, including pH and an abundance of soluble cations that can precipitate P, is of major concern in how it affects P availability in the soil solution. Using fertigation, we have clearly demonstrated that a 5:1:0:0.5 ratio of N:P2O5:K2O:S maximizes nutrient-use efficiency when applied through irrigation water at a rate of 10 to 12 lbs/in of N from first square through the third week of flowering. It was rather interesting that the 5:2 ratio produced lower yields across all water supplies during the three years of this experiment, compared with the 5:1 or 5:3 N:P ratios (Figure 3). The 5:2 ratio is what both private labs and the Texas Cooperative Extension Service have recommended for 40 years to West Texas cotton produc- ers, based upon all P being applied preplant, usually broadcast. Dr. Krieg is professor of crop physiology in the Plant and Soil Science Department of Texas Tech University.
Fluid Journal 2002-2004
Fluid Journal 2008-2009