Effect of nitrogen fertiliser and cultivation method on root systems of rice subjected to alternate wetting and drying irrigation

Abstract

AbstractBetter management of water and fertiliser is of critical importance for root systems development of rice, which is its first line of defence against water deficit and plays a key role in water and nutrient acquisition from soil. Two pot experiments were conducted to investigate the morphological response of root systems of rice under different doses and timings of N fertiliser application as well as cultivation methods subjected to alternate wetting and drying (AWD) irrigation. The treatments for the first pot experiment included two lowland Thai rice varieties (Pathumthani 1 and RD57), five N application doses (0, 30, 60, 90 and 120 kg N ha−1) and three cultivation methods (dry direct seeding [DDS], wet direct seeding [WDS] and transplanting [TP]). In the second pot experiment, root systems response of the same rice varieties was evaluated under four timings of N application (one‐split: 100% at basal; two‐split: 75% at basal and 25% at active tillering; three‐split: 50% at basal, 25% at active tillering and 25% at panicle initiation; and four‐split: 25% at basal, 25% at active tillering, 25% at panicle initiation and 25% at early flowering or before heading) applied at 60 kg ha−1 using the same cultivation methods. In both experiments, plants were subjected to AWD irrigation in which soil water potential was fluctuated between saturated condition (but not flooding) and −5 kPa. Pathumthani 1 developed better root systems (longer roots and higher root length density [RLD]) than RD57 regardless of N doses and cultivation methods. DDS resulted in higher root number, root dry matter (RDM) and root to shoot ratio at 120 kg N ha−1, whereas the same root traits were better at 90 kg N ha−1 under WDS. TP had better root systems development at 60 kg N ha−1. N application in four splits maximised root growth with more in number and longer roots as well as higher RLD, RDM and root to shoot ratio regardless of varieties and cultivation methods. Both rice varieties were equally suitable for growing when established under DDS, WDS and TP subjected to AWD irrigation with better root systems development at 120, 90 and 60 kg N ha−1, respectively. N application in four splits at 60 kg ha−1 enhanced root systems development. This study revealed that N fertiliser dose and application schedule may need to be adjusted depending on cultivation method when water‐saving irrigation technique is to be used in rice production system.