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a Univ. of Florida, Inst. of Food and Agric. Sciences, Dep. of Agronomy, Gainesville, FL 32611 (C. M. Cherr current address: Univ. of California, Graduate Group in Ecology and Dep. of Plant Sciences, Davis, CA 95616)
b Univ. of Florida, Inst. of Food and Agric. Sciences, Dep. of Entomology and Nematology, Gainesville, FL 32611
* Corresponding author (jmscholberg{at}ifas.ufl.edu)
Received for publication January 28, 2005.
Legumes utilized as GM may provide on-farm organic N. Nonetheless, data regarding GM use on sandy soils in warm-temperate environments remains scarce. We conducted a 2-yr field study to evaluate growth and decomposition of sunn hemp (Crotalaria juncea L.), blue lupin (Lupinus angustifolius L., winter 20012002), and Cahaba white vetch (Vicia sativa L., winter 20022003) used as GM to provide N for sweet corn (Zea mays L. var Rugosa) in a reduced tillage system in northern Florida. Intercepted solar radiation accounted for most variability in total GM dry weight and N content regardless of species or year. Sunn hemp exhibited substantial growth and N accumulation (
12.2 Mg ha1 and 172 kg N ha1 in 14 wk). However, rapid N loss (4558% within 4 wk after death) occurred after sunn hemp death. Winter GM growth (2.04.0 Mg ha1 and 51104 kg N ha1 in 1820 wk) appeared limited by low LAI response to growing degree days (GDD) and was not affected by previous sunn hemp GM. Sunn hemp residues and living winter legume together contained 120 to 125 kg N ha1 at time of final sampling before sweet corn planting. Corn rotated with sunn hemp plus winter GM and supplemented with 133 kg synthetic N ha1 produced marketable ear yields similar to monoculture corn fertilized with 200 kg synthetic N ha1, but the practical value of this benefit is low. In northern Florida, winter and/or summer GM use may substitute only for a relatively small portion of synthetic N rates.
Abbreviations: C, sweet corn GDD, growing degree days GM, green manure L, winter legume LAI, leaf area index PAR, photosynthetically active radiation SH, sunn hemp WAD, weeks after death WAE, weeks after emergence
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