Dynamics of carbon, water, and water use efficiency (WUE) fluxes for Maize crop under partial root zone drying irrigation

Quantifying carbon and water dynamics as well as their interaction (water use efficiency: WUE) fluxes will help in evaluating alternate irrigation practices. This study is aimed at understanding the role of two partial root zone drying irrigation methods practiced in two dominant soils (red sandy and black cotton) on WUE dynamics observed at two spatial scales, i.e. leaf and plant. To achieve this, maize plants were grown in controlled pots for two seasons (monsoon and winter) with three irrigation treatments i.e. conventional irrigation (CI), alternate partial root zone drying irrigation (APRD) and fixed partial root zone drying irrigation (FPRD) in two soils, i.e. red sandy soil and black cotton.  Leaf gas exchange parameters such as: net CO₂ assimilation rate (A_n), stomatal conductance (g_s), transpiration (T_r), vapor pressure deficit of leaf (VPD_L), and leaf temperature (T_leaf) were monitored along with the plant parameters such as: biomass, soil moisture and leaf area index (LAI). Results showed that highest WUE_L of 272.76± 20.51 µmol CO₂ mol^-1 H₂O is observed with APRD irrigation in red sandy soils which is 1.2 to 1.33 times higher than in black cotton soils. At plant level, biomass in black cotton soils is 1.67 to 1.70 times higher than in red sandy soils. In contrast, water consumption in back cotton soils was 1.70 to 1.72 times higher than in red sandy soils. Red sandy soils showed a higher WUE_P of 197± 10.5 g L^-1. Stomatal conductance, leaf temperature and vapor pressure deficit of leaf are found to be the controlling drivers of WUE_L.  Similarly, irrigated water and leaf area index are found to be the key drivers of WUE_P. Results conclude that, APRD irrigation can significantly improve WUE both at leaf and plant scales. Of the two soils, red sandy soils outperformed in achieving higher WUE at both spatial scales. Our results concluded that consideration irrigation practices, and soil characteristics is indispensable for accurate and simultaneous characterization of WUE.