Yield-contributing Factors in Lowland Irrigated Rice as Affected by Variety, Water Management, and Fertilizer Rate in Agusan Soil

Abstract

Rice grain yields in irrigated areas of Agusan del Norte/Sur provinces ranged at only 3.3–3.8 t/ha in 2010–2019 – hence the need to study the yield potential of varieties, appropriate water management, and optimum fertilizer rates to improve such yields. This study assessed the effects of rice varieties, water management, and fertilizer rates on grain yield and agronomic parameters. It also recommended variety, water management, and fertilizer rate for improving grain yields in Agusan soil. Screenhouse experiment was done using lowland rice soils collected from Remedios T. Romualdez, Agusan del Norte, Philippines. The experiment was laid out in unbalanced randomized complete block design with three factors: [1] PSB Rc 18, NSIC Rc 122, and PSB Rc 82 for the variety factor; [2] continuous submergence (CS) and alternate wetting and drying (AWD) for the water management factor; and [3] PalayCheck (PFR) and farmers’ fertilizer rates (FFR) for the fertilizer rate factor. Three replications each for PSB Rc 18+CS+PFR, PSB Rc 18+CS+FFR, PSB Rc 18+AWD+FFR, NSIC Rc 122+CS+FFR, NSIC Rc 122+AWD+FFR, PSB Rc 82+CS+PFR, PSB Rc 82+CS+FFR, and PSB Rc 82+AWD+FFR plus four replications each for PSB Rc 18+AWD+PFR, NSIC Rc 122+CS+PFR, NSIC Rc 122+AWD+PFR, and PSB Rc 82+AWD+PFR were employed. Data on chlorophyll (chl) levels, plant height, tiller count, and number of healthy and unhealthy leaves were gathered weekly. Yield component data, including panicle lengths and dry weight of all filled grains or grain yields, were determined before and after harvesting. Dry weight of straw and roots were also assessed. Compared with PSB Rc 82, PSB Rc 18 had a significantly higher grain yield by 9% due to enhanced protection of chloroplast structure, leading to longer leaf area duration and higher chl contents across growth stages (GSs). These contributed to an improved “sink” or significantly greater number of grains per panicle by 19% and enhanced “source” or better health status of leaves. Improved “source” increased the grain filling efficiency, resulting in a significantly higher number of filled grains per panicle by 18%, grain weight per panicle by 21%, and harvest index by 6%. In contrast with AWD, CS had a significantly higher grain yield by 7% due to higher soil nitrogen availability leading to better yield-contributing plant traits. These traits include a significantly longer vegetative stage by 3%, greater straw biomass by 9%, higher leaf chl levels, and better health status of leaves from grain filling until harvesting. Moreover, the lower number of small, unproductive tillers in CS allowed more plant resources to be used for improving the health of large, panicle-bearing tillers. Compared with FFR, PFR had a significantly higher grain yield by 18% due to a closer-to- the-optimum fertilizer rate leading to an improved “source.” Improved “source” includes the following statistically significant parameters: [1] higher number of tillers by 7–18%, greater number of healthy leaves, and higher total number of leaves throughout GSs; [2] greater biomass by 15%; [3] higher chl content from booting until grain filling stage; and [4] better health status of leaves from booting until harvesting. The closer-to-the-optimum fertilizer rate also improved the “sink,” which was the significantly higher number of productive panicles by 16% and longer panicles by 2%. The study implies that certain management practices – employing a more adapted variety, CS or PFR in Agusan soil – provides a better genetic or environmental factor, which enhances plant traits and improves grain yields. Management recommendations are as follows: [1] PSB Rc 18 should be selected over PSB Rc 82 because it is more adapted in Agusan soil, [2] CS should be preferred over AWD in a non-zinc-deficient Agusan soil, and [3] the 74-28-43-24 kg N-P2O5-K2O-S/ha PFR should be selected over the 42.0-4.5-10.5-3.8 kg N-P2O5-K2O-S/ha FFR. Variety, water management, and fertilizer rate do not have significant two- and three-way interaction effects on grain yield; hence, no specific combination of the three factors can be recommended.