Effects of contrasting N-enriched biochar applications on paddy soil and rice leaf phosphorus fractions in subtropical China.

Biochar has been proved to be an important soil amendment to alleviate soil phosphorus (P) in the paddy crops. However, the role of specially prepared biochar (N-enriched biochar) on the distribution and transformation of P soil in and rice leaves needs to be revealed. In this study, we studied in a field experiment the effects of two different levels of application of N-enriched biochar on the P fractions of soil and leaves. The results showed that: (1) in early rice, both rates of N-enriched biochar increased soil concentrations of labile inorganic P (Pi) (+51.5 % and +66.2 %, respectively) and labile organic P (Po) (+167 % and + 76.9 %, respectively) and moderately labile Pi (+37.8 % and +27.8 %, respectively) and decreased soil concentration of moderately labile Po (-17.0 % and -52.7 %, respectively) in the 0-15 cm layer. Soil total P concentration was positively correlated with soil labile P fractions and moderately labile Pi concentrations (p < 0.05); (2) in early and late rice, application of the biochar at 4 t ha-1 increased rice leaf concentration of inorganic (+13.3 % and +34.8 %, respectively), nucleic acid (+24.2 % and +13.0 %, respectively) (p < 0.05). The foliar inorganic and nucleic acid P concentrations were positively correlated with foliar total P concentrations; (3) redundancy analysis showed that with the application of N-enriched biochar, soil total carbon (C), nitrogen (N) and P concentration were important factors affecting the chemical forms of soil P, while soil organic matter, soil total P and leaf total P content were important factors affecting the chemical forms of leaf P; (4) allometric growth models showed that under the application of N-enriched biochar, 0-30 cm soil labile Po concentration was positively related to leaf concentration of nucleic acid P, 0-15 cm soil moderately labile Pi concentration was positively related to leaf concentration of inorganic P and nucleic acid P. Thus, this study provides evidence that N-enriched biochar increase the soil P-availability of labile and moderately labile P that in turn improved rice plants P use efficiency.

[Characteristics of Soil Carbon, Nitrogen, Phosphorus, and Ecological Stoichiometry in Vegetable Fields and Orchard in the Coastal Area of Fuzhou].

The soil ecological stoichiometric characteristics of different agricultural land use types have a certain indicator function for characterizing the level of soil nutrient supply and are of great significance to the management of nutrient resources in farmland ecosystems. In order to reveal the soil carbon (C), nitrogen (N), and phosphorus (P) contents and their ecological stoichiometric characteristics in different vegetable fields and orchard agricultural land use types, this study took vegetable fields (taro field and jicama field) and orchards (citrus tree orchard, watermelon field, and pear tree orchard) as the research objects in the coastal area of Fuzhou City. The contents of soil C, N, and P and their ecological stoichiometric characteristics in different vegetable fields and orchard agricultural land uses were measured and analyzed. The soil C and N contents were in the order of orchard>vegetable field (P<0.05). The C content in the citrus tree orchard was the highest (4.44 g·kg-1), and the N content in the watermelon field was the highest (1.46 g·kg-1). The soil P content was vegetable field>orchard (P<0.05), and the jicama field had the highest P content (0.19 g·kg-1). The soil carbon and nitrogen ratio (C/N), carbon and phosphorus ratio (C/P), and nitrogen and phosphorus ratio (N/P) were orchard>vegetable field (P<0.05). Among them, the citrus tree orchard had the highest C/N (7.40) and C/P (61.43), and the watermelon field had the highest N/P (10.27). Soil N content was significantly and negatively correlated with bulk density and conductivity (r=-0.49, r=-0.28, P<0.05), and there was a significant and positive correlation with soil water content (r=0.61, P<0.05). C/P and C/N were significantly and positively correlated with SOM (r=0.71, r=0.64, P<0.01). In the process of crop planting and management in the coastal area of Fuzhou City, it is necessary to reasonably add nitrogen fertilizer to compensate for the N limitation, and slow-release nitrogen fertilizer is better for promoting the sustainable supply of nitrogen nutrients in the growth and development of crops.