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Crop management practices influence the amount and quality of organic matter and the state of aggregation in soils. The objective of this study was to determine the early changes in organic and microbial‐biomass C contents and in water‐stable aggregates of two loamy soils (Typic Fragiaquept and Typic Haplaquept) following plowing of a meadow and subsequent planting of either corn (Zea mays L.) or barley (Hordeum vulgare L.). The effects of 1, 2, and 3 yr of cropping with these two crops were compared with an undisturbed and a recently plowed meadow. Plowing decreased the organic and microbial‐biomass C contents of the surface soil (0–6 cm) by an average of 40 to 50%, but, when the whole surface horizon (0–24 cm) was considered, there was no effect. Further cropping with either corn or barley resulted in no net loss of organic matter and microbial biomass but only a redistribution in the surface soil profile. Microbial‐biomass C was not preferentially affected by cropping relative to total organic C. The mean‐weight diameter of water‐stable aggregates decreased not only with plowing but also with length of cropping both in the surface soil (0–6 cm) and throughout the top 24 cm. There was little difference in the specific effects of the two crops on organic C, microbial‐biomass C, or aggregation.

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A two‐year study was conducted to assess the effect of hog manure on the losses of nitrogen and phosphorus in runoff and drainage from grain‐corn (Zea mays L.) plots, and the importance of spring versus annual loads. Treatments consisted of mineral N‐P‐K fertilizer applied at rates of 152 kg N ha‐1, 35 kg P ha‐1, and 86 kg K ha‐1; and hog (Sus scrofa domestica L.) manure applied preplant or post‐emergence (six‐to‐eight leaf stage), at 152 kg N ha‐1, 39 kg P ha‐1, and 112 kg K ha‐1. The plots were rototilled (7 cm depth) in spring to incorporate fertilizer and preplant hog manure, and fall chisel‐plowed (15 cm depth) to incorporate chopped corn residues. They were arranged in a completely randomized plot design. Flow volumes and nutrient levels in runoff and drainage waters were monitored year round but occurred mainly during the snowmelt (March 25‐April 9), and post.snowmelt (April 10‐May 13) periods. Of the total amount of water lost during snowmelt, 90 percent was in runoff, while 92 percent occurred as drainage in the post‐snowmelt period. Sixty‐five percent of the total annual volume of water lost was lost during these two periods as runoff and drainage. Treatments did not affect the annual snowmelt or post‐snowmelt N and P loads. Total annual loads averaged 8.0 kg TKN ha‐1, 1.8 kg NH4‐N ha‐1, 43 kg NO3‐N ha‐1, 0.4 kg TP ha‐1, and 0.15 kg PO4‐P ha‐1. Spring (snowmelt and ost‐snowmelt) runoff and drainage loads averaged 2.9 kg TKN ha‐1, 1.2 kg NH4‐N ha‐1, 18 kg NO3‐N ha‐1, 0.25 kg TP ha‐1, and 0.04 kg PO4‐P ha‐1, which were 40 percent to 70 percent of the yearly nutrient loads. Therefore, the hog manure management systems examined were of no greater threat to the environment than mineral fertilizers. However, spring N and P losses do represent an important part of the annual nutrient loss budget, even with conservation practices.