Soil organic carbon (SOC) is essential for soil fertility and climate change mitigation, and carbon can be sequestered in soil through proper soil management, including straw return. However, results of studies of long‐term straw return on SOC are contradictory and increasing SOC stocks in upland soils is challenging. This study of North China upland agricultural fields quantified the effects of several fertilizer and straw return treatments on SOC storage changes and crop yields, considering different cropping duration periods, soil types, and cropping systems to establish the relationships of SOC sequestration rates with initial SOC stocks and annual straw C inputs. Our meta‐analysis using long‐term field experiments showed that SOC stock responses to straw return were greater than that of mineral fertilizers alone. Black soils with higher initial SOC stocks also had lower SOC stock increases than did soils with lower initial SOC stocks (fluvo‐aquic and loessial soils) following applications of nitrogen‐phosphorous‐potassium (NPK) fertilizer and NPK+S (straw). Soil C stocks under the NPK and NPK+S treatments increased in the more‐than‐20‐year duration period, while significant SOC stock increases in the NP and NP+S treatment groups were limited to the 11‐ to 20‐year period. Annual crop productivity was higher in double‐cropped wheat and maize under all fertilization treatments, including control (no fertilization), than in the single‐crop systems (wheat or maize). Also, the annual soil sequestration rates and annual straw C inputs of the treatments with straw return (NP+S and NPK+S) were significantly positively related. Moreover, initial SOC stocks and SOC sequestration rates of those treatments were highly negatively correlated. Thus, long‐term straw return integrated with mineral fertilization in upland wheat and maize croplands leads to increased crop yields and SOC stocks. However, those effects of straw return are highly dependent on fertilizer management, cropping system, soil type, duration period, and the initial SOC content.

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This study was initiated to investigate the effect of nitrogen fertilizer on agronomic efficiency, yield and yield components of barley after faba bean precursor crop. A field experiment was carried out in 2015 main cropping season at district at Ayba and Tek'a kebeles in Tigray Regional State, Ethiopia. The experiments were arranged in a randomized complete block design with three replications. Treatments were six levels of nitrogen (0, 11.5, 23, 34.5, 46 and 69 kg N ha-1). Soil samples were collected before planting and analyzed for selected physicochemical properties. Pre-planting soil analysis results revealed that total N was low at Tek'a kebelle (0.09%) and medium at Ayba (0.186%). The organic carbon content of experimental fields was medium at Ayba and low at Tek'a. Application of nitrogen had significantly influenced yield and yield components of barley at Tek'a site but not at Ayba after fababean precursor crop. This is consistent with the initial soil nitrogen and contribution of the precursor crop for nitrogen fixation. The highest agronomic efficiency was recorded from the addition of 23 kg N ha-1 (31.52 kg kg-1) and 34.5 kg N ha-1 (31.44 kg kg-1) at Ayba kebelle and Tek'a, respectively. Both biological and partial budget analysis depicted that application of 34.5 kg N ha-1 was found to be economical. Therefore, application of nitrogen after legume crop should consider initial soil result..

Article InformationCrop rotation is a common practice in the study area, but there is no enough information on the specific rate of nitrogen to be applied after legumes for wheat production. Hence, on farm field experiments were conducted to determine the amount of nitrogen fertilizer rates needed for bread wheat after chick pea, grass pea, fababean and field pea precursor crops. The field experiments were conducted during 2014 main cropping season at Hawzien after chick pea and grass pea and at Emba Alaje after fababean and field pea precursor crops. The experiment consists of six nitrogen rates (0, 11.5, 23, 34.5, 46 and 69 kg Nha -1 ) laid in a RCBD with three replications. Phosphorus, sulfur and potassium fertilizers were also applied as basal for all plots at sowing. Surface soil samples were collected before planting and analyzed for selected soil properties. Soil analysis result of the experimental sites revealed that total nitrogen content (%) of the soil after chickpea-wheat (0.0695), grass pea-wheat (0.067), fababean-wheat (0.074) crop rotation were categorized under low range and after field pea-wheat (0.102) under medium range. Application of nitrogen had significantly increased grain and straw yield at Hawzien district after chick pea and grass pea precursor crops. At Emba-Alaje the highest grain yield was recorded on plots treated with 69 kg N ha -1 (6242 kg ha -1 ). Grain and straw yields of wheat increased up to a rate of 46 kg N ha -1 after fababean at Emba-Alaje district. There is no significant difference in grain and straw yields of wheat due to application of nitrogen after field pea crop rotation. In Hawzien the highest agronomic efficiency after chick pea and grass pea was recorded from plots treated with 46 kg N ha -1 and 34.5 kg N ha -1 , respectively. In Emba Alaje the highest agronomic efficiency after faba bean and field pea was recorded from plots treated with 11.5 kg N ha -1 and 23 kg N ha -1 , respectively. At Hawzien, the partial budget analysis revealed that application of 46 kg N ha -1 for bread wheat after chick pea and grass pea was economical with 1545% and 796 % marginal rate of return, respectively. At Emba Alaje, the partial budget analysis revealed that application of 34.5 kg N ha -1 for bread wheat after fababean was economical with 895% marginal rate of return. It could be concluded that application rate of N for wheat after leguminous crops should consider initial soil N and precursor crop.