Straw burial depth and manure application affect the straw-C and N sequestration: Evidence from 13C &15N-tracing

Abstract

Straw return to farmlands has great potential to increase C sequestration and decrease its losses. Combined influences of straw burial depth and manure application are important factors which determines the decomposition or retention of straw C and N in the soil profile. The influence of straw amendment on soil-derived C and N is not well- known in the presence of manure application with at different straw burial depths. In a 360-day field study an in situ 13C &15N-tracing technique was used to elucidate the effects of straw burial depth (15 and 35 cm), manure (presence or absence) and their interaction on C and N sequestration. Soil organic carbon (SOC) and total nitrogen (TN) contents were significantly (P < 0.05) higher in treatments including manure plus straw (SMS) compared to the soil (S), soil plus straw (SS) and soil plus manure (SM) treatments at both soil burial depths. After 360 days, straw N sequestration was unaffected by burial depth, but significantly more straw C was sequestrated at the 35 cm soil depth compared with the 15 cm soil depth: 39.9 % vs. 35.8 %, respectively. The straw-derived C was 37.9 % for the SS treatments and it was lower, 2.2–10.0 % and 5.7–13.7 % for the SMS treatments at depths of 15 and 35 cm, respectively. The mean residence time of the C and N was longer, 16 and 27 days, respectively at the 15 cm soil depth and 31 and 37 days, respectively at the 35 cm depth in the SMS treatments, compared to the SS treatments. Hence, the SMS treatments improved stability of carbon and nitrogen in deep soil layers. We concluded that returning straw at subsurface soil increased straw C sequestration in soils; combining the application of manure with returning straw to deep soil layers improves the stability of organic C and N in soil without compromising the potential for carbon and nitrogen sequestration.