Abstract
Application of suitable nitrogen (N) fertilizer application rate (NR) with respect to sowing time (ST) could help to maximize the performance and productivity of upland rice in Southern Thailand. The 2-year experiments were conducted in the sheds to evaluate the agronomic responses of the upland rice genotype, Dawk Pa–yawm, under various combinations of NR and ST between 2018–2019 and 2019–2020 aimed at obtaining sufficient research evidence for the improved design of long-term field trials in Southern Thailand. As with the initial research, four NR were applied as N0 with no applied N, 1.6 g N pot−1, 3.2 g N pot−1 and 4.8 g N pot−1, and experiments were grown under three ST including early (ST1), medium (ST2) and late sowing (ST3). Results from the experiments indicate that the application of 4.8 g N pot−1 resulted in maximum grain yield under all ST in both years. However, a maximum increase in grain yield was observed under ST2 by 54–101% in 2018–2019 and by 276–339% in 2019–2020. Maximum grain N uptake of 0.57 and 0.82 g pot−1 was also observed at NR 4.8 g N pot−1 under ST2 in both years, respectively. Application of NR 4.8 g N pot−1 resulted in the highest N agronomic efficiency (NAE), nitrogen use efficiency (NUE) and water use efficiency (WUE). However, the performance of yield and yield attributes, N uptake, N use efficiencies and WUE were declined in late sowing (ST3). Significant positive association among yield, yield attributes, N uptake and WUE indicated that an increase in NR up to 4.8 g N pot−1 improved the performance of Dawk Pa–yawm. The results suggest that the application of 4.8 g N pot−1 (90 kg N ha−1) for upland rice being grown during September (ST2) would enhance N use efficiencies, WUE and ultimately improve the yield of upland rice. However, field investigations for current study should be considered prior to general recommendations. Moreover, based on the findings of this study, the importance of variable climatic conditions in the field, and the variability in genotypic response to utilize available N and soil moisture, authors suggest considering more levels of NR and intervals for ST with a greater number of upland rice genotypes to observe variations in field experiments for the precise optimization of NR according to ST.
Highlights
Rice (Oryza sativa L.) contributes half of the world’s staple food [1,2]
Based on the significance of nitrogen application rate (NR), sowing time (ST), limited research evidence availability and the wide range of NR and ST management practices in Southern Thailand, we understood that adjustments in NR with modification in ST and synchronizing their interactions could result in improved nitrogen use efficiency (NUE), water use efficiency (WUE) and yield
[47] In our experimental results, it was noticed that grain yield was in an increasing trend up to NR 4.8 g N pot−1, indicating the need for an increase in further levels of NR in future experimentation to observe the curve for better optimization of the N application rate
Summary
Rice (Oryza sativa L.) contributes half of the world’s staple food [1,2]. Rice production is increasing continuously [2,3]. To avoid under or excessive application of N which results in a decline in grain yield or agronomic and economic losses, respectively, proper nutrient management is necessary [27] In this regard, estimating plant N concentrations and uptake could help to identify optimum NR for maximized nitrogen use efficiency (NUE). Based on the significance of NR, ST, limited research evidence availability and the wide range of NR and ST management practices in Southern Thailand, we understood that adjustments in NR with modification in ST and synchronizing their interactions could result in improved NUE, WUE and yield. The results of the current research will help to adjust the appropriate gradients for NR and intervals for ST for better designing of further long-term, multilocational field trials and propose best and optimized N and ST management practices for enhanced upland rice production, especially in Southern Thailand
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