Impact of alternative wetting and soil drying and soil clay content on the morphological and physiological traits of rice roots and their relationships to yield and nutrient use-efficiency

Abstract

Rice is threatened by the inefficient use of water and fertilizer. However, understanding the effects of water regimes and soil clay contents on morphology and physiology of plant roots and their relations to yield and nutrient use-efficiency is essential to improve rice productivity. In this regard, three experimental soils were conducted with three soil clay content levels, namely, light clay (S LC), medium clay (S MC), and heavy clay (S HC), and three irrigation regimes, namely, alternate wetting and 0% soil drying (AWSD0%), alternate wetting and 10% soil drying (AWSD10%), alternate wetting and 30% soil drying (AWSD30%) over July-October in 2018. The experiment was a randomized complete block design in a factorial arrangement with three replications. The results showed that responses of roots and shoots and the nitrogen (N), phosphorus (P) and potassium (K) uptake of rice were significantly affected by the water regimes and soil clay contents. Under the same water regime, root morphology and physiology, biomass production and NPK utilization of rice were higher in high clay soil than light clay soil. Under the same soil clay content, AWSD0% regime was the optimal water management practice for growing rice, providing the highest grain yield. Whereas, AWSD30% regime was improper water management option for rice, offering the lowest grain yield. The combination, AWSD0%×S HC, resulted in the greatest values of the apparent recovery efficiency (ARE) of NPK applied, at AREN (43.4%), AREP (20.4%) and AREK (67.2%), as well as the highest values of partial factor productivity (PFP) of NPK, applied, at PFPN (19.7, g g−1), PFPP (31.9, g g−1) and PFPK (41.1, g g−1) respectively. Conversely, the treatment AWSD30%×S LC resulted in the lowest values of ARE of NPK applied at AREN (8.3%), AREP (3.0%), and AREK (6.7%), as well as the lowest values of PFP of NPK, applied at PFPN (7.0, g g−1), PFPP (11.9, g g−1) and PFPK (12.2, g g−1) respectively. Root length density, root weight density, root active absorption area, root oxidation ability, and root surface phosphatase were higher in AWSD0%×S HC than that in AWSD70% × S LC. While the former combination increased NPK contents in the rhizosphere, the latter their reduced availability due to the increment in pH and redox potential of the soil. The results are important for rice water management option in the paddy clay soil. The results also suggest that the adoption of alternate wetting and soil drying regimes should guarantee morphological and physiological improvements in root traits, by which contributes to greater biomass production, larger NPK acquisition and, thus better NPK utilization of rice.