Summer Cover Crops Shoot Decomposition and Nitrogen Release in a No-Tilled Sandy Soil

Abstract

Cover crops have numerous benefits when used in a no-till system. Understanding the processes of decomposition and N release of summer cover crops (SCC) may help select species and management to be used in cropping systems. This study aimed to evaluate C and N loss of SCC shoots. Six SCCs were evaluated: velvet bean (Mucuna aterrima), pearl millet (Pennisetum americanum), dwarf pigeon pea (Cajanus cajan), sunn hemp (Crotalaria juncea), showy rattlebox (Crotalaria spectabilis), and jack bean (Canavalia ensiformis). The experiment was conducted for two years under no-till in soil classified as Typic Hapludalf (Argissolo). The C and N remaining of crop shoots were evaluated for 140 days using litter bags and the results were fitted with a simple nonlinear regression model. Elevated air temperature and rainfall volume accelerated C and N loss in the first year. Carbon and N loss was characterized by a rapid initial phase followed by a slower one. Jack bean had the highest C loss rates, while the lowest rates were found in pearl millet. Velvet bean and pearl millet had the lowest N loss rates in the first year, together with showy rattlebox in the second year. The rates of C (kC) and N (kN) loss were positively correlated with total N and water-soluble C and N in crop shoots. During the 35 days after cover crop termination, SCCs released 35 to 137 kg ha-1 N in 2010 and 5 to 66 kg ha-1 N in 2011. Velvet bean and showy rattlebox showed more gradual N release, which may favor the synchronization between N release and N uptake by the succeeding crop. The sunn hemp was the legume species that combined higher remaining residues on the soil surface, releasing less N but preventing soil erosion.

Cover crop diversity for sustainable agriculture: Insights from the Cerrado biome

“…The maintenance of biomass on the soil surface is mainly controlled by the amount of biomass production and the decomposition rate, which depends on biotic and abiotic factors such as residue quality (C/N ratio and cellulose, lignin and hemicellulose contents), soil biological activity and the edaphoclimatic conditions, mainly temperature and rainfall (Carvalho et al., 2010). The lower C/N ratio of legume crops favours rapid decomposition compared to grass crops (Weiler et al., 2019). Thus, because of the faster degradability of legume residues (half‐life time of 82 days), the soil can be uncovered at the beginning of the cash crop development, but the nutrients will be quickly released and may be available for soybean.…”

The Potential of Three Summer Legume Cover Crops to Suppress Weeds and Provide Ecosystem Services—A Review

“…This accumulated nitrogen was released during decomposition, with 7.5 to 19% being taken up by the following crop, resulting in a 25 to 68% increase in maize yields [69]. In addition, velvetbean releases nitrogen gradually, which promotes synchronization between nitrogen release and nitrogen uptake by the following crop [70]. Another benefit of a velvetbean cover crop relies on species' effects on insect and nematode populations.…”

Cover crop influence on nutrient cycling, nematode population and soybean yield in the Brazilian Cerrado

“…The maintenance of biomass on the soil surface is mainly controlled by the decomposition rate will depend on biotic and abiotic factors such as plant composition (C/N ratio, cellulose, lignin, and hemicellulose content), soil biological activity, and the edaphoclimatic conditions, mainly temperature and rainfall (Carvalho et al 2010). The low C/N ratio of legume crops (usually smaller than 20) favors rapid decomposition compared to grass crops (C/N ratio greater than 25) (Weiler et al 2019). Thus, due to the higher decomposition of the legume residues (half-life time of 82 days), the soil will be unprotected at the beginning of the cash crop development, but the nutrients will be quickly released and become available for cash crop.…”