Reducing soil CO2 emission and improving upland rice yield with no-tillage, straw mulch and nitrogen fertilization in northern Benin

Abstract

To explore effective ways to decrease soil CO2 emission and increase grain yield, field experiments were conducted on two upland rice soils (Lixisols and Gleyic Luvisols) in northern Benin in West Africa. The treatments were two tillage systems (no-tillage, and manual tillage), two rice straw managements (no rice straw, and rice straw mulch at 3 Mgha 1 ) and three nitrogen fertilizers levels (no nitrogen, recommended level of nitrogen: 60 kgha 1 , and high level of nitrogen: 120 kgha 1 ). Potassium and phosphorus fertilizers were applied to be non-limiting at 40 kg K2O ha 1 and 40 kg P2O5ha 1 . Four replications of the twelve treatment combinations were arranged in a randomized complete block design. Soil CO2 emission, soil moisture and soiltemperature were measured at 5 cm depth in 6–10 days intervals during the rainy season and every two weeks during the dry season. Soil moisture was the main factor explaining the seasonal variability of soil CO2 emission. Much larger soil CO2 emissions were found in rainy than dry season. Notillage significantly reduced soil CO2 emissions compared with manual tillage. Higher soil CO2 emissions were recordedinthemulched treatments. SoilCO2 emissionswerehigher infertilizedtreatmentscompared withnon-fertilizedtreatments.Ricebiomass and yieldwerenot significantlydifferent as a functionoftillage systems. Onthe contrary, rice biomass andyieldsignificantly increased withapplication of rice straw mulch andnitrogen fertilizer.Thehighest response of rice yield to nitrogen fertilizeradditionwas obtained for60 kg N ha 1 in combination with 3 Mgha 1 of rice straw for the two tillage systems. Soil CO2 emission per unit grain yield was lower under no-tillage, rice straw mulch and nitrogen fertilizer treatments. No-tillage combined with rice straw mulch and 60 kg N ha 1 could be used by smallholder farmers to achieve higher grain yield and lower soil CO2 emission in upland rice fields in northern Benin.