Above and belowground litter decomposition of cover crops grazed at different intensities

Abstract

Grazing cover crops may increase land-use efficiency while promoting sustainability. We investigated how grazing intensity affects cover crop litter quantity, quality, decomposition, and cotton (Gossypium hirsutum L.) N uptake. Cover crops were a mixture of rye (Secale cereale L.) and oat (Avena sativa L.) managed as follows: no grazing +34 kg N ha⁻¹ (NG34), no grazing +90 kg N ha⁻¹ (NG90), heavy grazing (HG), moderate grazing (MG), and light grazing (LG). Grazed treatments received 90 kg N ha⁻¹. After cover crop termination, above- and belowground litter was collected and incubated in situ for 0, 4, 8, 16, 32, 64, and 128 days, with cotton plants sampled on the same days to estimate N recovery and synchrony between N release from litter and uptake by cotton. By Day 128, only 13% of initial NG34 aboveground biomass had disappeared, whereas 42% of HG disappeared. Nitrogen retained in aboveground litter of HG was less than NG90 (27 vs. 60 kg N ha⁻¹), and aboveground final N stock (at Day 128) of HG was less than NG90 and LG (16, 47, and 41 kg N ha⁻¹, respectively). Belowground litter contributed 98 kg N ha⁻¹ versus 46 for aboveground. Belowground N disappearance from litter bags was greater from NG90 than NG34 (39 vs. 21 kg N ha⁻¹). Cotton N uptake by Day 128 was similar across treatments (191 kg N ha⁻¹). Grazing cover crops impact aboveground litter quantity, quality, and decomposition rates, and belowground litter plays an important role on the N cycling.