The residual effects of crop residues on N availability and crop growth are largely unknown. A field experiment was conducted from 1986 through 1988 at Lincoln, NE, to determine the residual effects on no‐till corn (Zea mays L.) production and N uptake of 0, 50, 100, and 150% of the amount of crop residues produced by the previous crop during the previous 5 yr. These effects were evaluated with and without tillage (disking), N fertilizer (60 kg N ha−1), and hairy vetch (Vicia villosa Roth ssp. villosa, ‘Madison’) winter cover crop. Increasing the previous crop residue rate increased organic C, total N, and NO3‐N in the upper 30 cm of soil as much as 10, 12, and 66%, respectively. Growth and N uptake by corn (3‐yr average) generally increased as previous residue rate increased. Corn grain and stover production was 17 and 25% greater for the highest compared with the lowest previous residue rate. Uptake of indigenous soil N, but not fertilizer N, also increased as previous residue rate increased. Cover crops generally increased growth and N uptake with no fertilizer, but had little effect with N fertilizer. Soil properties, crop growth, and N uptake generally were not affected by tillage or interactions among the variables. These results indicate that increasing no‐till crop residue rates increased the capability of this soil to provide N to growing crops for many years. It appears this effect is somewhat self‐perpetuating.

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Poultry manure applied alone or in combination with urea at different N levels was evaluated as a N source for wetland rice grown in a Fatehpur loamy sand soil. Residual effects were studied on wheat which followed rice every year during the three cropping cycles. In the first year, poultry manure did not perform better than urea but by the third year, when applied in quantities sufficient to supply 120 and 180 kg N ha -1, it produced significantly more rice grain yield than the same rates of N as urea. Poultry manure sustained the grain yield of rice during the three years while the yield decreased with urea. Apparent N recovery by rice decreased from 45 to 28% during 1987 to 1989 in the case of urea, but it remained almost the same (35, 33 and 37%) for poultry manure. Thus, urea N values of poultry manure calculated from yield or N uptake data following two different approaches averaged 80, 112 and 127% in 1987, 1988 and 1989, respectively. Poultry manure and urea applied in 1:1 ratio on N basis produced yields in between the yields from the two sources applied alone. After three cycles of rice-wheat rotation, the organic matter in the soil increased with the amount of manure applied to a plot. Olsen available P increased in soils amended with poultry manure. A residual effect of poultry manure applied to rice to supply 120 or 180 kg N ha -t was observed in the wheat which followed rice and it was equivalent to 40 kg N ha -1 plus some P applied directly to wheat.

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The results of four field experiments conducted for 2 or 3 years on two soils, loamy sand (Typic Ustipsamments) and silty clay loam (Natric Ustochrept) showed that in rice, application of N in three equal amounts was more efficient than one or two applications, irrespective of source of N and type of soil. The results further showed that application of the first dose of N 7 days after transplanting rice was more beneficial than its application at transplanting. Calcium ammonium nitrate was significantly inferior to urea and/or ammonium sulphate for rice in both soils. There were no significant differences in wheat yield, N concentration or uptake due to time and source of N application.