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Fluid Journal : Fluid Journal 1996-1998
3 Fluid Journal Fall 1998 total P loss was sediment-associated. Only about 5 percent of the sediment- associated P was bioavailable. Soluble P losses were highest for no- till, intermediate for ridge-till, and least for chisel-disk (Figure 4). Loss of soluble P in chisel-disk was least because of the incorporation of broadcast P. In ridge-till, where fertilizer P was only partially covered by shaving of the ridge at planting, soluble P losses were moderate. In no- till, where broadcast P remained exposed on the soil surface, soluble P losses were nearly six times greater than in the control. In contrast, deep-banded P increased soluble P losses only slightly over the control in all of the tillage systems. Placement of P below the critical zone of mixing between surface soil and runoff water significantly reduced soluble P loss. Bioavailable P loss followed the same general pattern as soluble P, since nearly all of the bioavailable P was associated with the soluble P fraction. Nearly all of the soluble P loss occurred during the first couple of runoffs after P fertilizer was applied, and diminished significantly with subsequent runoff events. The results of this study emphasize the importance of subsurface placement or fertilizer r in conservation tillage systems to minimize total and soluble P losses. In tilled systems, fertilizer P should be subsurface applied or incorporated before first runoff occurs. Following are several practices and tools that can help keep fertilizer and manure P in place: • subsurface apply or incorporate prior to first runoff • avoid buildup of soil test P to extremes • periodically invert P-stratified soils • use buffer strips, terracing, contour tillage, cover crops, conservation tillage, and impoundment where appropriate. Dr. Stewart is Great Plains Director; PPI; Dr Janssen is professor, Kansas State University; Dr Polizotto is chief agronomist, PCS Sales. Editor's note: This article shows how improved fertilizer-use efficiency and high yields go hand in hand with minimal environmental impact. Continued support of FFF research and education programs provides additional data on the importance of fertilizers in food and fiber production and the compatibility of that production with environmental quality. Broadcast P Deep band P Check Chisel-disk Ridge-till No-till Tillage System P loss (grams/A) 0 100 200 300 400 500 600 Figure 3. Total P losses as influenced by tillage and P placement (3-year aver- age), Kansas. Figure 4. Soluble P losses as influenced by tillage and P placement (3-year average), Kansas. Broadcast P Deep band P Check Chisel-disk Ridge-till No-till Tillage System P loss (grams/A) 0 20 40 60 80 100 120 140
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