| Popis: |
There is a lack of data on conservation tillage under field conditions characteristic of a dairy operation. Thus, simulated rainfall was used to compare total P (TP), algal-available P (AAP), and dissolved molybdate-reactive P (DMRP) losses from the conventional, chisel, and no-till systems for corn both with and without surface-applied manure prior to tillage. Rainfall was applied at several times during the growing season of 1978 and 1979. A portion of the previous year's residue was removed in 1978 and all the residue was left in 1979. Concentrations and losses of TP and AAP among unmanured tillage treatments were similar to trends observed for sediment concentrations and losses. In 1978, the chisel and notill systems were ineffective in reducing TP and AAP losses relative to the conventional system. In contrast in 1979, lower TP and AAP losses occurred from unmanured chisel and no-till sites relative to unmanured conventional sites. In both years of the experiment, surface spread manure increased DMRP concentrations where the manure was not completely incorporated by tillage. In contrast, little difference was observed in DMRP concentrations among unmanured treatments. Manure also increased AAP concentrations for no-till but had only a slight effect and no effect for the chisel and conventional systems, respectively. AAP concentrations from manured sites followed the order no-till > conventional = chisel. Differences in runoff volumes among treatments influenced P losses. Runoff losses were relatively high for no-till, particularly after planting, and losses of DMRP and AAP were very high where manure was surface applied. Often, runoff was reduced for the chisel system relative to other tillage systems, and consequently these reductions increased the effectiveness of this system in reducing P losses. Additional Index Words: conservation tillage, no-till, chisel, best management practices, nonpoint pollution, water quality, rainfall simulation. Mueller, D. H., R. C. Wendt, and T. C. Daniel. 1984. Phosphorus losses as affected by tillage and manure application. Soil Sci. Soc. Am. J. 48:901-905. N in runoff from agricultural lands can contribute to overfertilization of receiving waters (Loehr, 1974). Of the elements known to influence algal growth, there is general agreement that phosphorus (P) is the key nutrient in limiting eutrophication in the Great Lakes Region (Wetzel, 1975; Schindler, 1977). Thus, reducing the amount of available and potentially available P in runoff is a logical means of reducing the impact of agriculture on rates of eutrophication. The majority of P in agricultural runoff is normally attached to sediment. Because of this, erosion control practices show promise for reducing total P (TP) in runoff and, presumably, TP inputs to surface waters. Normally, however, not all of the TP in runoff is 1 Research supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin-Madison, Madison, WI 53706, and by U.S. EPA Grant no. G005139-01. 2 Program Coordinator, Dep. of Soil Science, Univ. of WisconsinMadison; former Project Associate, Dep. of Soil Science, Univ. of Wisconsin-Madison and currently Soil Scientist, USDA-ARS, Columbia, MO; and Associate Professor, Dep. of Soil Science, Univ. of Wisconsin-Madison, respectively. equally available to aquatic plants. Soluble inorganic P is considered to be the most readily available P form (Wetzel, 1975). A portion of the sediment-bound P may also become available by desorbing from sediment as soluble levels are depleted (Sonzogni et al., 1982). Most runoff studies have emphasized soluble P and/or TP as indicators of the pollution potential of runoff (Klausner et al., 1974; Olness et al., 1975). Chemical extractants developed to test P availability in soils have also been applied to sediments (Burwell et al., 1975; Barisas et al., 1978). However, a lack of calibration data for aquatic plants make the results of these tests uncertain. Recently, a routine method has been developed for estimating the relative availability of sediment-bound P forms (Huettl et al., 1979). Use of such a method should allow for a more adequate assessment of the pollution potential of surface runoff and, thus, improve the evaluation of management alternatives for reducing the amount of pollutants in runoff from agricultural land. Recently, conservation tillage (CT) methods have received considerable attention as management alternatives for reducing pollutant loads in agricultural runoff. Many of these practices have been shown to reduce erosion and, as a result, TP losses (Romkens et al., 1973; Siemens and Oschwald, 1976). However, studies have also shown that soluble P concentrations and losses may be greater with CT (Romkens et al., 1973; Barisas et al., 1978; McDowell and McGregor, 1980). These researchers concluded that higher concentrations of soluble P were attributable to a lack of incorporation of fertilizer P and to a release of P from unincorporated crop residues. Research by Timmons et al. (1973) supports the contention that unincorporated fertilizer P and crop residues can contribute to higher soluble P concentrations in runoff. Surface applications of fertilizer P may also increase concentrations of available P on eroded sediment. Studies by Barisas et al. (1978) and Johnson et al. (1979) found that available P concentrations in sediments increased with decreasing tillage where fertilizer P was broadcast. This tended to compensate for the lower soil losses from CT and resulted in sediment P losses which were similar among tillage systems. A recent study by Baker and Laflen (1982) found that injecting fertilizer P eliminated any influence of this input on levels of dissolved and sediment available P. Most studies of CT systems have been performed under field conditions characteristic of corn grown by a cash grain farmer. Residue is usually left, fertilizer P is commonly surface applied, and there is seldom application of animal wastes to cropland. In the Great Lakes Basin and particularly in Wisconsin, many dairy and livestock fanners remove a portion of crop residue for feed or bedding purposes. They also commonly dispose of animal wastes by surface applications. The companion paper showed that soil losses were reduced for chisel and no-till systems relative to the conventional system when manure was surface applied (Mueller et al., 1984). Often the reductions were |
Plný text