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Fluid Journal : Fluid Journal 2005-2007
Fall 2005 Is K the Cinderella Nutrient for Reduced-Till Systems? Drs. Douglas Karlen and John Kovar Summary: A preliminary evaluation in 2003 and additional soil-testing in 2004 showed K stratification in the soil profile for the till- and slot-plant treatments. Whole-plant samples at the V6 growth stage in 2003 showed low K concentrations, but low rainfall during reproductive growth stages (grain-fill) mitigated or masked any yield response to postemergence (V10) rescue applications of potassium thiosulfate (KTS). In 2004, 30-lb/A broadcast, dry band, or liquid band applications were compared with a control (0 lb/A K2O) for both corn and soybeans. Use of sodium-saturated cation exchange membranes successfully quantified K movement and positional availability. All methods of providing additional K increased whole-plant (V6) and corn ear-leaf K concentrations as well as grain yield compared to the control. We conclude that K is being neglected and limiting yield when reduced-till is used on these soils. All methods of providing additional K increased whole plant and corn ear-leaf K concentrations as well as grain yield. Fluid Journal 1 The potential for K deficiencies with reduced-till, especially for corn, is a well-documented soil fertility problem. However, with increased emphasis on N and P management because of their potential off-site effects, researchers, consultants, and farmers may have begun to overlook the importance of K as compared to N and P. We raise this issue because in the spring of 2000, technicians managing the ARS-National Soil Tilth Laboratory (NSTL) field research program noted that following emergence of soybeans planted in a long-term (>30 yr) tillage study at the Iowa State University- Agronomy and Agricultural Engineering Research Center (ISU-AERC), plants in no-till (slot-plant) and till-plant treatments were showing much greater stress than those planted into moldboard, chisel, or springdisked treatments. The problem was initially attributed to herbicide carryover since Balance WDG had been applied to corn in 1999. In 2001, similar problems occurred in the same tillage treatments after corn emergence. Weed science specialists were consulted, but after observing the plots they concluded the problem was not herbicide related. 2002 to 2003 In an effort to determine what was causing the slot- and till-plant treatments to have slower early season growth and generally lower yields, a fertilizer blend (16-40-40) was deep- banded (6 inches) below the surface or broadcast with and without the tillage associated with banding to subplots within both tillage treatments in autumn of 2002. The 2003 early-season plant growth response to banded fertilizer was so striking that additional soil test and plant analyses were made. Incremental soil analyses in 2003 (Table 1) confirmed that K was very stratified in both tillage treatments. A postemergence "rescue" treatment Table 1. Soil test stratification measured in 2003 within slot- and till-plant plots near Ames, Iowa. Depth Bluk Density Organic Matter pH Bray P Exchangable K Inches g/cm3 % ppm 0to2 1.19 4.16 6.53 52 176 2to4 1.24 3.81 6.61 29 96 4to8 1.58 3.68 6.28 19 65 Table 2. Soil test stratification measured in 2004 within slot- and till-plant plots near Ames, Iowa. Depth Bluk Density Organic Matter pH Bray P Exchangable K Inches g/cm3 % ppm Continuous Corn 0to2 1.15 43.8 6.24 50 199 2to4 1.35 38.6 6.32 38 119 4to8 1.42 36.1 6.16 14 83 Corn/soybean rotation 0to2 1.16 46.2 6.56 43 192 2to4 1.26 41.9 6.49 34 119 4to8 1.42 39.5 6.32 17 107
Fluid Journal 2002-2004
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