Irrigated rice rotations affect yield and soil organic carbon sequestration in temperate South America

Abstract

Rice (Oryza sativa L.) systems rotated with perennial pastures have intensified in South America to increase annual grain productivity, but the effects on rice yield and soil quality remain poorly understood. We evaluated rice grain yield, crop and pasture biomass production, and soil organic carbon (SOC) and total nitrogen stocks (0-15-cm depth) in three rice-based rotations over 8 yr in Uruguay. Treatments were: (a) rice-pasture [a 5 yr rotation of rice-ryegrass (Lolium multiflorum Lam.)-rice, then 3.5 yr of a perennial mixture of tall fescue (Festuca arundinacea Schreb.), white clover (Trifolium repens L.), and birdsfoot trefoil (Lotus corniculatus L.)], (b) rice-soybean [a 2-yr rotation of rice-ryegrass-soybean (Glycine max [L.] Merr.)-Egyptian clover (Trifolium alexandrinum L.)], and (c) rice-cover crop (an annual rotation of rice-Egyptian clover). Rice after soybean or pasture achieved the highest yield (9.8 Mg ha -1 ), 9% higher than rice after rice in the rice-pasture and rice-cover crop systems. Estimated belowground biomass under rice-pasture (2.7 Mg ha -1 ) was 12 and 42% greater than under rice-cover crop and rice-soybean rotations, respectively. Rice-pasture showed an increase of 0.6 Mg ha -1 yr -1 of SOC; no changes were observed in the intensified rotations replacing pasture with additional rice or soybean. All systems sustained soil total N. These results provide insights for implementing sustainable rice-based rotations, with rice-pasture being the only system that increased SOC while achieving high rice yields and belowground biomass productivity.

Measured and modeled nitrogen balances in lowland rice-pasture rotations in temperate South America

“…Such systems have a greater potential for efficient nutrient use and cycling than the intensive single commodity systems that have become dominant globally over the last decades (Martin et al, 2016;Ghimire et al, 2021). For example, until recently rice production in Argentina, Paraguay and southern Brazil was predominantly a monoculture, shifting in the last decade to more complex systems with the inclusion of soybeans or short pastures with livestock (Denardin et al, 2020;Ribas et al, 2021;Macedo et al, 2022). This diversification has helped improve soil conditions, weed control, and farm income, though nutrient management still needs to be improved (De Faccio Carvalho et al, 2021).…”