Residue Decomposition and Phosporus Release From Cover Crops.

Cover crops (CC) are employed in agricultural settings to protect soil from erosion and to reinforce the soil carbon pool. In no-tillage systems, CC residues remain over the soil surface increasing soil cover and diminishing soil water evaporation. CC may also modify soil nutrient cycling because cover crops uptake nutrients in their available forms and return them as residues with variable degree of availability. Most nutritional studies on cover crops have focused on nitrogen and less attention has been given to non-mobile nutrients as phosphorus (P). The objective of this work was to evaluate the dynamics of plant residues decomposition and P release from different CCs. Field experiments were carried out on a sandy-loam soil (Typic Hapludoll) located at Gral Villegas (North West of Buenos Aires Province, Argentina) where soybean is cultivated as monoculture. Treatments compared were: no CC, oat (Avena sativa), rye, (Secale cereale) and ryegras (Lolium moltiflorum). Residue decomposition and nutrient release from plant residue was evaluated by the litter bag method. Litter bags were placed on the soil surface after CC were chemically dried with gliphosate and then collected at 30, 70, 100, 140, 170, 295 y 340 days. Rye and oat were the most productive CC (4943 ± 754 y 4120 ± 183 kg dry matter ha-1). Rye and ryegrass residues showed higher P concentration than oat although the total plant P in residues content was smaller in ryegrass. Decomposition rate was higher in oat than in rye but similar to ryegrass. At the end of the experimental period (340 days) about half of rye residues remained on the soil. P release was fast during the first stage of residue decomposition and then tended to slow down for all CCs. P release rate from residues was higher in rye than in oat and ryegrass. Obtained results indicated that the processes of biomass decomposition and P mineralization are not coupled, but closely related. After 340 days, rye and oat released around 70% of P contained in their residues whereas ryegrass released almost 100%. Overall, rye was the species with the best performance as CC, combining high productivity and slow decomposition. 1