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Fluid Journal : Fluid Journal 1999-2001
2 Fluid Journal Summer 1999 Plot size important We used and compared conven-tionally-tilled corn plots near Tifton, Georgia, sized on two scales. The meso-plots measured 6,692 sq. ft. and the micro-plots 60 sq. ft. They were smaller than agricultural fields but had flow lengths sufficiently long to produce rill erosion as in fields, and, therefore, were large enough to investigate both tillage and crop effects. Smaller plot experi-ments have the potential to estimate greater losses than those measured in the whole watershed experiments, because they are generally simulating conditions that are severe and, therefore, rarely encountered in field studies. The micro- plots were adjacent to but separated hydrologically from the meso-plots. Micro-plots were treated simultaneously and identically with meso-plots. Losses come early Losses of NO3-N and soluble-P were massive one day after fertilizer application and then decreased markedly (note the spikes in Figures 1 and 2). Much of the day one loss was likely direct movement and dissolution of granular fertilizer with runoff. One of the most interesting aspects of the data is that there was no increase in NO3-N loss after application of 105 lbs/A of N as UAN at day 28. These data suggest that granules at or near the soil surface are more susceptible to movement in extreme runoff than liquids, which are quickly absorbed by the soil. Losses of bioavailable-P were greatest at day 14 in the meso-plots and day 29 in the micro-plots. These losses were largely sediment bound. Following five 1.97-inch incremental applications of irrigation water applied after fertilization, total loss in meso-plot runoff amounted to 1.4 percent of the applied N as NO3-N, 3 percent of the applied P as soluble-P, and 5.1 percent of the applied P as bioavailable-P. Losses for meso- and micro-plots were equal for NO3-N and Micro-plots 2 1.0 1 0.5 0 0.0 NO -N 3 NO -N 3 Soluble-P Soluble-P Bio available-P Bio available-P Loss (lbs/A) Loss (lbs/A) -20 0 -8 20 1 40 14 Day Day Meso-plots 60 29 80 49 100 108 120 Figure 1. Losses of NO3-N, soluble-P, and bioavailable-P in lbs/ A of applied N and P, data means of two replications and two years, Gascho, st al. , University of Georgia, 1992-93.
Fluid Journal 1996-1998
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