Green mulching of cover crops in rice: effects on weed germination and emergence

Background:  Organic rice weed management can be addressed through winter cover crops (CC). In spring, rice is seeded, CC are terminated and the field is flooded. CC residues provide a mulching layer that can reduce weed emergence, but the degradation of the biomass may also reduce weed germination through the release of organic acids.

Objective:  The objective of the study is to evaluate the effect of flooding water after CC degradation on weed germination and emergence.

Methods:  The study included both field and greenhouse trials and lasted 2 years. CC were Italian ryegrass, hairy vetch and a mixture of both. In the field, water was sampled in two locations, 5 and 10 days after flooding, and used in germination tests on weedy rice (Oryza sativa). In the greenhouse, a simulation of the technique was performed in buckets filled with paddy field soil: some received the CC degraded water only, others had both the water and the CC mulch layer. Water was sampled after 7 days for germination trials and total weed density in the buckets was assessed.

Results:  The germination of weedy rice was not affected by the flooding water (>92.5%). Total weed density in the buckets was reduced only when the CC mulch was present.

Conclusions:  The flooding water sampled after the degradation of the cover crop biomass did not affect weedy rice germination, both in field and in greenhouse conditions. If the CC mulch is absent, the flooding water alone is not able to reduce weeds.

Keywords:
Lolium multiflorum ; Vicia villosa ; Flooding; Organic Rice