Sustainability assessment on paddy-upland crop rotations by carbon, nitrogen and water footprint integrated analysis: A field scale investigation.

Nutrients of carbon, nitrogen and water of farmland ecosystem are essential foundation to guarantee crop production, but also environmental flows associated greenhouse gas (GHG), reactive nitrogen (Nr) releases, and water consumption. Their flow characteristics serve as a crucial starting point for creating efficient management practices and mitigation measures. Therefore, the objectives of this study are to quantify the carbon footprint (CF), nitrogen footprint (NF), water footprint (WF), and comprehensive environmental footprint (ComF) of six paddy-upland rotation systems, including fallow-paddy rice (FA-PR), Chinese milk vetch-paddy rice (CMV-PR), wheat-paddy rice (WH-PR), rapeseed-paddy rice (RA-PR), green forage wheat-paddy rice (WF-PR), and vicia faba bean-paddy rice (FB-PR), as well as to analysis their relationships and define driving factors. Results showed that the lowest area-scaled CF of 3.74 t CO2-eq ha-1 were observed in the CMV-PR rotation, which were 41% lower than that for WH-PR (the highest CF, 9.13 t CO2-eq ha-1) when soil carbon change was taken into account. It is of importance that soil carbon sequestration in CMV-PR rotation could offset up to around 57% of its CF, while the WH-PR rotation only offset 25%. The RA-PR rotation had the highest area-scaled NF and WF, which was 1.8 and 1.9 times greater than those of the lowest rotation in FA-PR. In terms of comprehensive environmental effects, the six rotation systems showed the order of FA-PR < CMV-PR < FB-PR < RA-PR < WF-PR < WH-PR, with NH3 volatilization accounting 60.7%-66.7% and blue-green WF for 17.5%-26.6% of the total. Therefore, priority should be given to optimizing N fertilizer application and water consumption for paddy-upland rotation systems. The study also suggested that appropriate inter-annual adjustment of rotation system could contribute to achieving GHG mitigations and Nr losses.

Assessment of productivity, nutrient uptake and economic benefits of rice under different nitrogen management strategies.

BACKGROUND: Integrating a chemical nitrogen (N) fertilizer with an organic fertilizer and using slow-release mechanism are important N management strategies to increase the N utilization efficiency (NUE) and grain yield of rice. However, the performances of both N management strategies on the productivity, the nutrient absorption and utilization efficiency, and the economic benefits of rice have not yet been comprehensively evaluated. METHODS: A 2-year field experiment was conducted with seven N management strategies without fertilizer (control), 100% conventional N fertilizer (conventional compound fertilizer and urea) (N100), 75% conventional N fertilizer with 25% organic-inorganic compound fertilizer (N75+OICF25), 50% conventional N fertilizer with 50% organic-inorganic compound fertilizer (N50+OICF50), 100% organic-inorganic compound fertilizer (OICF100), slow-release compound fertilizer with urea (SRCF+U), compound fertilizer with sulfur-coated urea (CF+SCU). The responses of the productivity, the nutrient absorption and utilization efficiency, and the economic benefits of rice to the different N management strategies were evaluated. RESULTS: CF+SCU performed comparably or better than N100, judging by the grain yield (GY), the N, phosphate (P) and potassium (K) agronomic efficiency (NAE, PAE and KAE), and the apparent N, P and K recovery efficiency (ANRE, APRE and AKRE). SRCF+U significantly increased the GY by an average of 7.7%, the NAE and the ANRE by 23.8 and 26.7%, the PAE and the APRE by 90.6 and 109.3%, and the KAE and the AKRE by 74.2 and 57.7%. The higher GY and nutrient utilization efficiency when using SRCF+U were attributed to the higher total biomass and total nutrient absorption. N75+OICF25 and N50+OICF50 produced a comparable grain yield than N100, whereas a significant yield reduction was observed when using OICF100. Compared with N100, N75+OICF25 resulted in a comparable or higher fertilizer use efficiency (0.3 and 4.7% for NAE and ANRE, 0.3 and 3.2% for PAE and APRE, 0.3 and -2.8% for KAE and AKRE). However, the fertilizer use efficiency when using N50+OICF50 and OICF100 were lower than with N100. The highest net return (NR) (5,845.03 yuan ha-1) and benefit to cost (B:C) ratio (0.34) were obtained when using SRCF+U. The NR and the B:C ratio when using N75+OICF25 were slightly higher than when using N100. However, N50+OICF50 and OICF100 significantly decreased the NR and the B:C ratio compared with N100 by 14.5 and 12.1% and by 35.1 and 29.0%, respectively. CONCLUSIONS: SRCF+U and CF+SCU enhanced the crop productivity, the nutrient uptake and utilization efficiency, and the economic benefits compared with N100. The comprehensive performance of SRCF+U was better than that of CF+SCU. N75+OICF25 produced almost similar productivity, nutrient uptake and use efficiency compared with N100. It demonstrated that N75+OICF25 stabilized the grain yield production of rice and reduced the input of chemical N fertilizer.