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Discussion and SummaryA few cases have been cited to illustrate the relationship of soils and their fertilization on the chemical composition of hay and pasture. Because of the mixed vegetation usually occurring in meadows and pastures, including the experimental plots, it was necessary to omit references to classic examples of the remarkable variations in the botanical and chemical composition of forage of different areas and of the well-being of the animals kept on them. However, enough comparable data have been tabulated or quoted to show that of the so-called major elements—N, P, K, and Ca—P is the one which is most frequently present in very small amounts in hays and pasturage. In different regions, varying circumstances make the P situation acute. In some the soil is too acid, in others too alkaline and in still others, the total supply of P in the soil is so low that only small amounts of P are available for plants and therefore only a sparse vegetation can exist. The liming of acid soils has in many instances, but not all, increased the availability of P to plants. A practical remedy for the unavailability of phosphates in alkaline soils does not seem to have been found, although some benefit has been obtained from liberal applications of S. Therefore, in some regions, means of overcoming deficiencies of available P constitutes a serious problem. On the other hand, this paper contains many examples of the remarkable effects of phosphatic fertilization on grassland. The lasting qualities of such treatments should be emphasized. Thus, it has been demonstrated that an application of 16% superphosphate at 500 pounds on the runout pastures of northeastern United States will increase the quantity and quality of the herbage for at least 14 years (5). Moreover, when superphosphate is the source of P, there is usually an increase in the Ca content of the grasses or legumes. In most of the humid areas, Ca is the next most important limiting element. The prevalence of legumes, particularly, is closely related to the level of exchangeable Ca in the soil. It has also been shown in this and other papers that indirectly the N content of grasses in mixed vegetation is dependent on a lime supply sufficient to permit a thrifty growth of legumes. Otherwise, recourse must be had to frequent applications of nitrogenous fertilizers. Although the pH of soils is not an accurate criterion of whether a species will thrive on them, it may be the most easily determined guide. The opinion is held here that pH should not be much below 5.5 for red clover and white clover and Lespedeza or below 6.0 for alfalfa and sweet clover. The value of Ca as a nutritive element has probably been under-emphasized. Better results may be expected with less acid conditions, not only directly, but indirectly through making it less likely that added phosphates will be fixed as more insoluble iron and aluminum compounds. Evidence of the adequacy of the available K supply in soils for forage plants is much more conflicting than it is for P and Ca. The tables contain many data showing wide differences in the K content of plants because of variations in soils or fertilization. Of the three major minerals, plants appear to absorb more K, both absolutely and relatively, than P or Ca. This is especially true with more mature plants such as are harvested for hay. In other words, “luxury” consumption is accentuated in the case of K. Another important consideration is that animals void a large part of the K consumed in their feeds. In this connection, there is some evidence that land runout by grazing is much less in need of K than adjacent areas depleted by removing the hay. However, on light soils or on soils under tillage for many generations, the successful growing of forage plants, particularly legumes, depends upon conserving and returning manure to the land or on applying potassic fertilizers. For example, alfalfa is very intolerant of low levels of available K in the soil and in some of the eastern states will not persist long unless K is supplied frequently by manure or fertilizers. In the middle west and especially the far west, the need for much fertilization with K has not yet become evident. The growth of grasses is likely to be increased appreciably by adding nitrogenous fertilizers. Usually the protein content of grasses, grazed or mowed in the vegetative stage (before heading) will be increased by such treatments. The chief disadvantages of this practice are that the effects only last a few weeks, the materials are relatively more expensive and the greatest returns per unit of N are obtained from spring applications or in a period when pastures are at their best. A nitrogen carrier may appreciably affect the concentrations of other elements in plants. Among forage crops, there are very few reported instances of plant deficiencies of other certainly necessary plant nutrient elements—Mg, Fe, Mn, S, B, Cu, and Zn. (Animals need still other elements such as Na, Co, Cl, and I, but usually it is necessary or expedient to supply them directly, not via soils and plants.) Probably this is due to the very small quantities needed and also to the fact that they are frequently present in fertilizers as impurities or parts of compounds containing major elements. However, soil deficiencies of these elements for pasture and hay crops have been reported. The availability to plants of many of these elements depends on the natural reaction of soils or amounts of lime added to them. This is especially true of Mn and B and only recently the so-called “over-liming” injury has been shown to be due, at least in some circumstances, to the unavailability of B on heavily limed soils (12). Minor element deficiencies appear to have been more common among legumes than grasses. From limited analyses one would conclude that normal legumes are richer in some of these elements. For example, McHargue (11) reports three or four times as much B in alfalfa as in bluegrass.

Organic C and nutrients in manure can improve degraded mine soil quality if they are retained in the soil. Composting manure or mixing manure with a high C/N ratio material before application could facilitate this improvement. The effects of these manure stabilization techniques on N and C retention in mine soil were investigated in two incubation experiments with six treatments: unamended soil, lime and fertilizer (14.3 Mg ha ―1 ), two rates of composted poultry layer manure (78 and 156 Mg ha ―1 ), and layer manure mixed with paper-mill sludge (PMS) (50 Mg ha ―1 manure, 102 and 183 Mg ha ―1 PMS) to provide C/N ratios of 20 and 30. In one experiment, amendments were laboratory applied just before incubation; in the other, amendments were field applied 1 yr before incubation. Carbon dioxide evolution and labile N and C were measured during incubation and microbial biomass N was determined at the end of the incubations. In laboratory-amended soil, all treatments produced similar quantities of labile N while compost and manure + PMS treatments resulted in stable soil N pools that were 2.5 to 2.7 times larger than in the unamended soil. In field-amended soils, stable N pools were similarly increased by compost and manure + PMS treatments. Large CO 2 production and microbial biomass N from manure + PMS treatments suggested that rapid microbial turnover of N was an important factor in stabilizing manure N. These results indicate that the combined manure + PMS amendment was as effective as composting in building stable N pools in mine soil.

Water-extractable P (WEP) in manure is correlated with P concentration in runoff from soils amended with manure and is, thus, an effective indicator of environmental P loss. This study sought to elucidate methodological factors affecting WEP measurement in manure and to quantify errors related to two established methods of manure WEP measurement. Dairy cow (Bos taurus) manure, poultry (Gallus gallus domesticus L.) (layer) manure, and swine (Sus scrofa domestica L.) slurry were used. Varying dry matter/distilled water ratios (1 to 20:200) revealed that greater dilution of manure dry matter increased WEP (mean 1.8-5.4 g kg -1 ), likely because of the dissolution of calcium phosphates. Increasing shaking time from 1 min to 24 h, increased manure WEP concentration (average 3.7-8.2 g kg -1 ). Filtration with Whatman 1 paper filters resulted in significantly higher WEP measurements in-dairy and poultry manure (4.1 g kg -1 ) than with a 0.45-μm filtration (3.7 g kg -1 ). No significant difference was observed in the swine slurry. A rainfall-runoff experiment using simulated rainfall was conducted to determine the effect of the individual factors on predicting dissolved-reactive P (DRP) concentration in runoff. Comparison of regression coefficients relating manure WEP to runoff DRP concentration revealed an optimum shaking time between 30 min and 2 h, but did not support any single manure/distilled water ratio or filtration method. Replication of two established methods of manure WEP measurement resulted in coefficients of variation of 0.01 to 0.12. Results of this study support the use of a single method with a fixed manure/distilled water ratio for liquid and dry manures.

There is uncertainty concerning evaluation of bioavailable P in manured soils. This study assessed P availability in manured Iowa soils by measuring soil P with agronomic and environmental P tests and P uptake by corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Soil and plant samples were collected at the V5-V6 growth stage from trials established at nine locations that received various rates of liquid swine (Sus scrofa) manure, and from farmers' fields that received other animal manures. Soil P was analyzed by the Bray-P1 (BP), Olsen (OP), and Mehlich-3 (M3P) agronomic tests, and by the Fe-oxide impregnated filter paper (FeP), anion-exchange resin membrane (RP), and water (WP) environmental tests. Soil P at a 15-cm depth ranged from deficient to 15 times optimum levels for crops. Extracted P was highest for BP, M3P, and RP, intermediate for OP and FeP, and lowest for WP. Relationships between soil P extracted by the tests were linear, trends were similar for manured and unmanured plots, and correlation coefficients were ≥0.70 (correlations were poorest for WP). There was no conclusive evidence for differences between tests in detecting manure-derived soil P at most sites. However, in some conditions BP, M3P, OP, and RP may extract proportionally more manured-derived P than FeP and WP. Only the agronomic tests were significantly correlated (0.42 for M3P, 0.44 for BP, and 0.47 for OP) with plant P uptake across sites. Agronomic soil tests would predict plant P availability for crops better than environmental P tests in soils receiving liquid swine manure.

We have collected solid-state 13 C nuclear magnetic resonance (NMR) data from the published literature (76 papers) and from our own results on 311 whole soils, physical fractions (25 clay-, 43 silt-, and 52 sand-size fractions) and chemical extracts (208 humic and 66 fulvic acids). Our purpose was to see whether a comprehensive analysis of data on >300 soils that ranged in organic C content from 0.42 to 53.9% would show any universal influence of management practice on the chemical composition of soil organic matter (SOM). The relative abundance of functional groups was calculated for the following chemical shift regions: 0-50 ppm (alkyls), 50-110 ppm (O-alkyls), 110-160 ppm (aromatics), and 160-200 ppm (carbonyls). There was a remarkable similarity between all soils with respect to the distribution of different forms of C despite the wide range of land use (arable, grassland, uncultivated, forest ), climate (from tropical rainforest to tundra ), cropping practice, fertilizer or manure application, and the different spectrometer characteristics and experimental conditions used. Functional groups in whole soils were always in the same abundance order despite the generally wide proportion range: O-alkyls (a mean of 45% of the spectrum, increasing with soil C content), followed by alkyls (mean 25%), aromatics (mean 20%), and finally carbonyls (mean 10%, decreasing with soil C content). Humic and fulvic acids contained much smaller proportions of O-alkyls than whole soils (means of 26%). Clay-size fractions were the most different from whole soils, being more aliphatic (+8%). Sand-size fractions generally gave very similar results to whole soils.

In many areas with confined animal operations, continual manure application has increased soil P above amounts sufficient for optimum crop yields. In these areas, it is of economic and environmental importance to determine how long high-P soils will remain above crop sufficiency and identify soils where P contents would decrease most rapidly under similar management conditions. Thus, the surface 5 cm of 23 high-P soils (85-419 mg kg -1 Mehlich-3 P) in Oklahoma and Texas, which had received beef feedlot, poultry, or swine manure (90-1880 kg P ha -1 yr -1 for up to 35 yr) were successively extracted with Fe-oxide-impregnated paper strips to investigate residual soil P availability. A decrease in strip P with successive extractions followed the equation: Strip P = a(extraction number) -b (r 2 of 0.88-0.98). The rate of P release to strips (exponent b) decreased more rapidly as soil P sorption saturation increased (R 2 of 0.79). Phosphorus saturation also accounted for 85% of the variation in the total amount of P released to strips from manured soils in 15 successive extractions (51-572 mg kg - 1). Fractionation of soil P before and after strip extraction showed bicarbonate inorganic P contributed most of the P released to strips (46%). The above equation also described soil P release in several published field studies (r 2 of 0.77-0.98). Thus, successive strip extraction of soil has the potential to describe soil factors controlling the availability of residual P and identify soils where high P contents may be less buffered and, thus, decrease more rapidly than others under similar management conditions.

Poultry production generates large amounts of litter or manure, which can be a valuable source of P for crops. However, litter application rates are usually based on data for mineral P fertilizer recommendations. In order to determine if this is agronomically and environmentally sound, the availability, fractions, and sorptivity of P from poultry litter or KH 2 PO 4 were determined in six Oklahoma soils following incubation for up to 28 d. An average 50% more P from KH 2 PO 4- treated (78 mg kg -1 ) than from leachate-treated soils (52 mg kg -1 ) was bioavailable, as determined by extraction with Fe-oxide-impregnated paper strips, after 28-d incubations. Conversely, more NaHCO 3- extractable P was found in leachate-treated (66 mg kg -1 ) than KH 2 PO 4 - treated soils (42 mg kg -1 ). Calculated from Langmuir isotherms, P sorption maxima averaged 548 mg kg -1 for leachate-treated and 304 mg kg -1 for KH 2 PO 4 -treated soils, while binding energies averaged 0.527 and 0.456 L mg -1 , respectively. The higher P sorption maxima and binding energies of leachate-treated soils may result from the formation of Ca-P complexes, given the increased Ca content of these soils. The different reaction in soil of P added as poultry litter leachate to that added as KH 2 PO 4 indicates manure application rates should be based on soil tests that are sensitive to P source-dependent sorption characteristics and/or manure trials, and not just on mineral fertilizer trials.

Soil organic matter (SOM) is valuable, because of both its beneficial effect on soil quality and crop productivity and its potential to sequester C. Long-term experiments provide an opportunity to identify crop management practices that enhance or degrade soil quality. This study was initiated in 1931 to determine residue management effects on crop yield and SOM (organic C and N) in a winter wheat (Triticum aestivum L.)-fallow system. The soil is a coarse-silty, mixed, mesic Typic Haploxeroll. Treatments include (units ha⁻¹ crop⁻¹) 22.4 Mg manure, 2.24 Mg pea vine residue, 0, 45, and 90 kg N with and without spring burning of straw, and 0 kg N with fall burning of straw. Yearly C and N inputs and removals have been determined since 1976, and calculated for prior periods. Soil C and N have been determined at ≈ 11-yr intervals. Manure, which supplies 111 kg N ha⁻¹ crop⁻¹, has consistently produced the highest yield and maintained the highest soil C and N contents. Other treatments initially yielded from 80 to 90% of the manure treatment, but have progressively declined in direct relation to decreasing soil N content. Low-fertility treatments currently yield from 43 to 57% of the manure treatment. The change in soil C and N with time is nearly linear for all treatments, and highly correlated with residue input. Treatment effects on soil C and N have been confined to the top 30 cm of soil, but there has been a slow steady decline in C and N in the 30- to 60-cm zone that is not related to residue management. Oregon State Univ. Agric. Exp. Stn. Technical Paper no. 10 132.

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