Amendment with controlled release urea increases leaf morpho-physiological traits, grain yield and NUE in a double-cropping rice system in southern China

Abstract
BACKGROUND
Understanding of mechanisms that underpin high-yielding cropping systems is essential for optimizing management practices. Currently, the contribution of plant traits such as leaf area, chlorophyll content and intercepted photosynthetically active radiation (PARi) to yield and nitrogen use efficiency (NUE) are not fully understood. In addition, the understanding of how canopy traits are affected by nitrogen (N) management practices is unclear. The present study aimed to determine the effect of amendment with controlled release urea (CR), common urea or no urea on NUE and plant eco-physiological characteristics in a 2-year field study in a double rice cropping system.

RESULTS
Regulation of N release through amendment with CR significantly increased grain yield, NUE and leaf morpho-physiological attributes. CR coupled with common urea (at comparable total N rates) increased leaf area index (LAI), relative chlorophyll content index (CCI) and PARi, leading to higher grain yield and NUE (increased 24.4% and 25.3% in early and late rice, respectively) compared to local farming practice. Structural equation model (SEM) analysis showed that differences in N application, between CR and common urea, directly accounted for differences observed in soil nutrient, PARi and NUE rather than yield components. Additionally, compared to traditional yield determinants, LAI and PARi (between booting and filling stage) are capable of predicting and explaining grain yield by 0.69 and 0.92 of R2 in early and late rice, respectively.

CONCLUSION
Leaf morpho-physiological traits are important for developing N management practices to increase NUE and improve food security for paddy agriculture in southern China. © 2022 Society of Chemical Industry.