Residue management is an important aspect of cropping systems. Availability of plant residue N to succeeding crops depends on N mineralization rates. Cooperative Extension currently recommends 22 to 67 kg N ha -1 credit to subsequent crops following peanut (Arachis hypogaea L.), but these recommendations are not supported in the literature, nor do they specify if the credit is applied to a subsequent winter or spring crop. Th e objective of this study was to assess N release rates from residues of three peanut cultivars (NC V-11, GA 02-C, and ANorden) at two placements (surface and 10-cm deep) and two locations representing northern and southern extremes of U.S. commercial peanut production (North Carolina and Alabama). Litterbags containing the equivalent of 3.5 Mg ha -1 were placed in a completely randomized design at both locations with four replications and retrieved periodically up to 335 d aft er application. Results were fi t to single or double exponential decay models. Based on empirical models, the N credit to a subsequent winter wheat (Triticum aestivum L.) crop was estimated at 14 to 19 kg N ha -1 when peanut residues were buried aft er harvest, and 19 to 24 kg N ha -1 when on the soil surface. When N credits were applied to a subsequent cotton (Gossypium hirsutum L.) crop, they were reduced to 2 to 9 kg N ha -1 (buried) and 6 to 10 kg N ha -1 (surface). Current recommendations are higher than the results obtained in this study suggest and warrant re-examination.

Fertilizer N efficiency of com (Zea mays L.) in conservation-tillage systems witb winter legumes such as crimson clover (Trifolium inctJr. lllllum L.) can possibly he improved by better synchronization of leg· ume-N release, fertilizer·N application time, and crop demand for N. The objective of this 3-yr (1986)(1987)(1988) field experiment was to deter· mine the effect of N application time on dry matter accumulation, N uptake, and grain yield of com grown in a winter legume conservation-tillage system. Com was planted witb unit planters into crimson clover residue following In-row subsoiling. The clover was killed at midbloom every year. Treatments were a factorial arrangement of fertilizer N rates and application time. Nitrogen as NH.N0 3 was broadcast at rates of 34, 67, and 134 kg ba-•. Zero-N checks were also Included in botb clover and rye (Seca/e cereol L.) plots. AppUcation times were at planting, or 3, 6, or 9 wk later. 1n addition, split applications (1/3 at planting and tbe remainder 6 wk later) of tbe 67 and 134 kg N ba-• rates were included. 1n 2 of 3 yr, dry matter accumulation was not affected by N application time. 1n 1987, how· ever, dry matter production was greater when N was applled at planting compared to split applications or appllcations later than 3 wk after planting. Application time affected N uptake patterns during the growing season, but generally did not affect total N uptake at the end of the season. With the exception of the first year, split N applications re-

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The tropical legume sunn hemp (Crotalaria juncea L.) cultivar 'AU Golden' has the potential to provide substantial nitrogen (N) to subsequent crops to reduce recommended application rates of synthetic N fertilizers. A mineralization field trial was conducted to measure mass decomposition and N and carbon (C) amounts remaining from sunn hemp residue following three planting dates (May, June, and July) during the 2013 growing season at the Tennessee Downloaded by [University of Manitoba Libraries] at 22:58 21 June 2016 ACCEPTED MANUSCRIPT 2 ACCEPTED MANUSCRIPT Valley (TVS) and Coastal Plain (WGS) locations of AL. Residue from June and July plantings contained 50. 0% and 61.1% N at WGS and 41.5% and 66.5% N at TVS by the end of their respective incubation periods compared to residue from the May planting, which contained 21.1% N at WGS and 47.8% at TVS. In order to create a more synchronous relationship between 'AU Golden' residue N mineralization and crop demand, termination must be delayed until approximate planting of the following crop.

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