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) (N(100)), 75% conventional N fertilizer with 25% organic–inorganic compound fertilizer (N(75)+OICF(25)), 50% conventional N fertilizer with 50% organic–inorganic compound fertilizer (N(50)+OICF(50)), 100% organic–inorganic compound fertilizer (OICF(100)), 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 N(100), 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. N(75)+OICF(25) and N(50)+OICF(50) produced a comparable grain yield than N(100), whereas a significant yield reduction was observed when using OICF(100). Compared with N(100), N(75)+OICF(25) 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 N(50)+OICF(50) and OICF(100) were lower than with N(100). 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 N(75)+OICF(25) were slightly higher than when using N(100.) However, N(50)+OICF(50) and OICF(100) significantly decreased the NR and the B:C ratio compared with N(100) 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 N(100.) The comprehensive performance of SRCF+U was better than that of CF+SCU. N(75)+OICF(25) produced almost similar productivity, nutrient uptake and use efficiency compared with N(100). It demonstrated that N(75)+OICF(25) stabilized the grain yield production of rice and reduced the input of chemical N fertilizer.