Suitability of Sunn Hemp as an Alternative Late‐Summer Legume Cover Crop

Abstract

The tropical legume 'Tropic Sun' sunn hemp (Crotalaria juncea L.) may have potential as an alternative legume cover crop or as forage for cattle in southern temperate regions. This study determined dry-matter production, chemical composition, and N release from sunn hemp residue under conventional and no-tillage systems as might be used in corn (Zea mays L.) production. Sunn hemp was sown in mid-August and mowed in early December on a Norfolk sandy loam (fine-loamy, siliceous, thermic Typic Kandiudult) and a Lucedale fine sandy loam (fine-loamy, siliceous, thermic Rhodic Paleudult) in Alabama (1991 1992). Mesh bags were used to determine residue decomposition and N release. Average dry-matter production was 5.9 Mg ha" 1 9 to 12 wk after planting. At mowing, residue N content averaged 126 kg ha~'. Residue overwintered on the soil surface until early April. During the first 4 wk following mowing, N release from residue was 50%. In April, N remaining in overwintered residue was only 38% of that after mowing in December (45 kg N ha' 1 ). Nitrogen release from residue during the subsequent corn growing season was 13% in no-tillage and 43% in conventional tillage. Sunn hemp produced sufficient dry matter to cover and protect the soil from erosion and provided sufficient N to benefit a succeeding summer crop. In addition, forage quality of leaves was suitable to provide late summer and fall grazing. Sunn hemp has potential to be managed as an alternative to winter legume cover crops in warm temperate regions.

Sequências de culturas em sistema de semeadura direta: II - decomposição e liberação de nutrientes na entressafra

“…No presente estudo, além da relação C:N, a análise das concentrações de lignina foi importante na caracterização dos materiais vegetais deixados sobre o solo, pois observou-se que os resíduos de crotalária, apesar de possuírem menor relação C:N, apresentaram baixas taxas de decomposição, devido às maiores concentrações de lignina em seus resíduos (Quadro 3). Mansoer et al (1997), ao particionarem plantas de crotalária após 12 semanas da semeadura, observaram maiores concentrações de lignina (184 g kg -1 ) e relação C:N (38) nos caules, quando comparadas às concentrações nas folhas da cultura (lignina = 64 g kg -1 e relação C:N = 11). Desse modo, no presente estudo, as maiores concentrações de lignina nos caules da crotalária proporcionaram menores taxas de decomposição.…”

Utilization of Sunn Hemp for Cover Crops and Weed Control in Temperate Climates

“…However, a major constraint to the use of winter legumes covers is the lack of ample growing time between cash crops (Mansoer et al 1997). Traditional planting windows for cover crops do not allow for maximum growth of cover crop species prior to the onset of cold temperatures; earlier planting of legumes would require a harvest of summer crops before maturity.…”

“…Traditional fall-seeded legume cover crops have limited biomass production prior to cold temperatures, which can limit N accumulation and availability to subsequent crops. Utilization of tropical legumes, such as sunn hemp, may allow for greater biomass production and N accumulation during the available growing season between fall harvest and onset of winter in temperate climates (Mansoer et al 1997). …”

“…Sunn hemp, a tropical legume that most likely originated from the Indo-Pakistani subcontinent, has been identified as a potential alternative to traditional legume cover crops employed in the southern portion of the United States (Cook and White 1996;Mansoer et al 1997;Montgomery 1954;Mosjidis and Wetje 2011). As a tropical legume, sunn hemp can produce larger quantities of biomass in a shorter time period than winter legumes from temperate zones, while still providing an agronomically important amount of fixed N (Mansoer et al 1997;Reeves et al 1996;Wang et al 2002b).…”

“…As a tropical legume, sunn hemp can produce larger quantities of biomass in a shorter time period than winter legumes from temperate zones, while still providing an agronomically important amount of fixed N (Mansoer et al 1997;Reeves et al 1996;Wang et al 2002b). The increased biomass production from sunn hemp would improve and extend weed control compared to other legume covers.…”