Land application of manure is a common practice in the Upper Midwest of the United States. Recently, there have been concerns regarding the effect of this practice on water quality, especially when manure is applied during winter over frozen soils. A study undertaken on a Rozetta silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalfs) at Lancaster, WI, evaluated the effects of tillage and timing of manure application on surface and subsurface water quality. The daily scrape and haul liquid dairy manure was applied either in the fall (before snow) or in winter (over snow with frozen soil underneath) to be compared with no manure under two tillage systems (no-till and chisel-plowing). In this paper, we report results on the effects of the above treatments on mineral N leaching. Percolation and mineral N leaching during the nongrowing season were, respectively, 72 and 78% of the annual losses, mainly because of the absence of plant water and N uptake. Percolation was generally higher from no-till compared with chisel-plow but there was no significant effect of tillage on mineral N concentration of the leachate or mineral N losses via leaching. Mineral N leaching was statistically higher from the manure-applied vs. no-manure treatment, but there was no difference between winter-applied manure and no-manure treatments. There were significant tillage by manure interactions with fall manure application followed by chisel-plowing resulting in highest N leaching losses. Averaged over the two years, N leaching rates were 52, 38, and 28 kg N ha(-1) yr(-1) from fall-applied, winter-applied, and no-manure treatments, respectively. These results show that there is substantial N leaching from these soils even when no fertilizer or manure is applied. Furthermore, fall-applied manure followed by fall tillage significantly increases N leaching due to enhanced mineralization of both soil and manure organic N.
Deep burrowing earthworm species have been found to be present in soils with a history of manure application. This study was designed to quantify the effects of long‐term application of liquid dairy manure and inorganic fertilizer on the distribution of earthworm macropores and in turn on the preferential transport of water and tracer through a typical soil of the karst area of the upper mid‐western USA. Large (≈ 30 cm diam. by 90 cm long) undisturbed soil columns were taken from plots where liquid dairy manure or inorganic fertilizers had been applied continuously for 8 yr. The number and size distribution of macropores in soil columns were nearly the same for both inorganic and manure treatments, however, visible surface macropores were continuous to much deeper depth in soil columns taken from manure than from the inorganic fertilizer plot. Identification of the earthworms a year later showed the presence of Apporectodea tuberculata, A. trapezoides, and Lumbricus rubellus, subsurface burrowers, as well as, L. terristris, a deeper burrowing species in the manure applied plot. Apporectodea tuberculata was the only species present in the inorganic fertilizer plot. Number of macropores and macroporosity varied with soil depth. The maximum macroporosity was <2.5% and it occurred at 2‐cm depth. The predominant macropore sizes were between 1‐ and 2‐mm radii for both treatments. During breakthrough experiments, Cl− appeared earlier in soil columns taken from the manure plot thereby indicating a greater continuity of macropores in the manure compared with the inorganic fertilizer treatment. Thearly appearance of Cl− in the manure treatment, however, was much slower than one would expect based on the number of macropores and their continuity estimated from the serial sectioning. This suggests that intrusive serial sectioning and image analysis techniques probably overestimate the continuity of macropores possibly due to vacuuming of the earthworm casts and other debris that plugs the macropore channels. Based on macropore size distribution with depth and related breakthrough curves, it is likely that most existing models of water and contaminant transport that simulate macropore flow, will not accurately predict the transport of water and contaminant because of their assumption that surface visible macropores are continuous to deeper soil depths. Data from this study showed that macropore size distribution could be described by a normal or log‐normal distribution function. These functions in combination with information on continuity and tortuosity of macropores may be sufficient, when used in some current macropore models, to adequately describe the conducting efficiency of macropores in soils.
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