Legume cover crop effects on temperate sugarcane yields and their decomposition in soil

Authors: White, Paul; WILLIAMS, GREGORY - LSU Agcenter; VIATOR, HOWARD - Retired Non ARS Employee; VIATOR, RYAN - Former ARS Employee; WEBBER III, CHARLES - Retired ARS Employee

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2020
Publication Date: 5/14/2020
Citation: White Jr, P.M., Williams, G., Viator, H., Viator, R.P., Webber III, C. 2020. Legume cover crop effects on temperate sugarcane yields and their decomposition in soil. Agronomy. 10(5):703. https://doi.org/10.3390/agronomy10050703.
DOI: https://doi.org/10.3390/agronomy10050703

Interpretive Summary: Sugarcane is a commercially important crop in Louisiana, Florida, and Texas, and the sugar produced is worth over $1 billion U.S. dollars annually. However, production practices that improve soil health are needed to maintain high yields. Historically, legume crops (e.g., soybean) were grown during fallow periods to boost grower income. Currently the practice is limited and does not include green manures, or legumes grown solely to benefit soil health. The purpose of this research is to evaluate how different legume green manure crops affect subsequent sugarcane yields. Also, a laboratory study was conducted to determine the optimal time between legume termination and sugarcane planting. Cowpea generally improved plant cane yields, but sunn hemp results varied. However, neither cover crop reduced sugarcane or sucrose yields consistently. The optimal planting window is 3 months, but can be lower at higher temperatures (32'). Overall, legume cover crops are an important component for sustainable sugarcane crops.

Technical Abstract: Sugarcane is commercially produced on 340,000 ha in the US and is valued at over $1 billion US annually. Cultural practices that improve sugarcane sustainability are needed to maintain yields in fields with degraded soils. Historically, leguminous rotation crops were used to provide organic matter and biologically-fixed nitrogen (N) for subsequent sugarcane crops. Currently, sugarcane is usually grown as a monoculture with only a short, 6-mo fallow period. The objective of these field studies was to determine how growing cowpea (Vigna unguiculate) and sunn hemp (Crotalaria juncea L.) as cover crops during fallow would affect the yield of subsequent sugarcane crops. A companion laboratory study investigated the decomposition rate of potential cover crops in soil at different temperatures. Cowpea and sunn hemp production averaged 12.8 t dry matter ha-1 and 250 kg N ha-1. Cowpea generally improved plant cane yields, but the effects of sunn hemp were more variable. However, neither cowpea nor sunn hemp reduced cane or sucrose yields consistently, and mineral N additions may have played a role in mitigating yield gains or losses. Based on laboratory incubation data, the average half-life for cowpea and sunn hemp would be approximately 3 mo. Overall, using leguminous cover crops should be viewed an important component for sustainable sugarcane practices.