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Fluid Journal : Fluid Journal 1996-1998
2 Fluid Journal Fall 1998 2,000 ppm to less than 1 ppm with the addition of alum, quick lime, slaked lime and several iron compounds. By reducing soluble P levels, transport of dissolved P from litter- treated fields may be decreased. In addition, decreased ammonia volatilization increases the N content and nutritive value of litter, and provides a material with an N:P ratio that more closely approaches crop requirements. Tillage practices affect erosion, runoff, and the loss of P from cultivated land. Increasing vegetative cover through conservation tillage may reduce P loss by reducing erosion and runoff. Figure 2 illustrates the effect tillage has on loss of various P fractions from runoff in the Southern Plains. Soil loss, particulate P, and total P losses were all reduced in no-till when compared to conventional tillage. In another study, conservation tillage reduced total P loss by controlling erosion. When compared to conventional tillage, no-till, chisel plow, and till-plant treatments reduced total P losses by an average of 81, 70, and 59 percent, respectively. Though reduced tillage may decrease runoff and erosion by increasing residue cover, an accumulation of residue and added P at the soil surface could also result in greater dissolved and bioavailable P losses via runoff. Field study A recent field study on grain sorghum and soybeans at the east central Kansas Experiment field near Ottawa evaluated the influence of different tillage systems (ridge-till, no-till, chisel-disk) and fertilization practices on P losses in runoff water over a three-year period. Total runoff varied with rainfall, tillage systems, and years. Runoff, on average, was highest in ridge-till and no-till, and lowest in chisel-disk. Tillage in the chisel-disk system increased infiltration and reduced runoff by drying and loosening the soil. Amount of rainfall that ran off was 18 percent for chisel-disk, 32 percent for ridge-till, and 30 percent for no-till. The higher runoff for conservation tillage contrasts with other reports of reduced runoff on soils with better drainage. On average, soil losses were 0.8 ton/A for chisel-disk, 0.6 ton/A for ridge-till, and 0.3 ton/A for no-till. Compared to chisel-disk, ridge-till lowered soil losses by 25 percent, and no-till by 60 percent. Losses of P in the runoff water also varied with rainfall, tillage system, fertilizer practices, and years. Average total P loss was highest with chisel-disk and ridge-till, and lowest for no-till (Figure 3). These differences generally parallel soil losses, since most of the -150 -95 31 Total P Particulate P Bioavailable P Dissolved P Soil Loss 308 -84 -65 Difference in P loss between no till and conventional till wheat,% -100 -50 0 50 100 150 200 250 300 350 Figure 2. Percent difference in soil and P loss in runoff from no-till and conventional-till wheat in Southern Plains, Sharpley, et at. , 1994. Figure 1. Processes involved in the loss of soluble and sediment P, Daniel, et al. , 1994.
Fluid Journal 1993-1995
Fluid Journal 1999-2001