Short‐statured Rice Response to Seeding and N Rates¹

Abstract

Research on response of direct seeded rice (Oryza sativa L.) to interactions of seeding rate and N rate is very limited, although considerable work has been done in the tropical countries with transplanted rice. Understanding responses by U.S. rice cultivars to these factors is important not only for optimizing management, but also because it provides information concerning the need for further improvement of plant type. Therefore, our objective in this study was to determine what factors might limit performance of ‘Starbonnet’ rice when subjected to a range of seeding and N rates. This study was conducted in field plots for 2 years on a Crowley silt loam soil (Typic Albaqualf) at the Univ. of Arkansas Rice Branch Experiment Station, Stuttgart, Ark. A split plot design was used. Time of N application (preplant or topdress) was the main plot and all possible combinations of seeding rates of 67, 135, and 303 kg/ha and N rates of 67, 135, and 202 kg/ha were the subplots. All treatments were replicated four times. The following measurements were taken: grain yield; stand counts prior to tillering and at maturity; blanks per panicle; florets per panicle; dry weight at heading and maturity; percent N in the flag leaf at heading; leaf area index (LAI) at heading Excessive vegetative growth before anthesis limited grain yield from dense plant populations. This was evidenced by high LAI at heading, reduced dry matter accumulation after heading, and adequate N levels in the flag leaf under conditions of dense population. Further indication of the effect of excessive vegetation prior to anthesis was shown by the fact that number of florets per panicle had more influence on grain yield than did blanks per panicle. Increasing the N rate from 135 to 202 kg/ha increased grain yield only for the 67 kg/ha seeding rate in 1972. Time of N application (preplant or topdress) did not influence grain yield. Under the direct seeding conditions of this study initial plant population, rather than tillering, accounted for the number of panicles per unit area. As seeding rate and plant population increased, number of florets and blanks per panicle decreased. Increasing the N rate increased both florets and blanks per panicle. Both increased seeding rate and N rate resulted in increased LAI. Under the conditions of this test the major factors that limited yield under dense population appeared to be light and CO2, since extra N fertilizer was ineffective.

Response of Spikelet Number per Panicle in Rice Cultivars to Three Transplanting Densities

“…A negative relationship between panicle number per unit area and SPP has been widely reported (Matsushima, 1966;Wells and Faw, 1978;Jones and Snyder, 1987), and we also found that the average panicle number per unit area was higher at high and medium planting densities. In each cultivar, although the differences in D-SPP and SPP values among planting densities were not statistically significant, D-SPP and SPP tended to be larger at the low planting density than at the high planting density, and, in contrast, panicle number per unit area were smaller at the low planting density than at higher planting densities.…”

“…Shiratsuchi et al (2007) reported a strong positive relationship between SPP and tiller dry weight at heading, and Yao et al (2000) also showed the similar relationship in 32 cultivars. In addition, a negative relationship between panicle number and SPP has been widely reported (Matsushima, 1966;Wells and Faw, 1978;Jones and Snyder, 1987). Therefore, the difference in the numbers of tillers and panicles that results from different planting densities should also affect the SPP (Kuroda et al, 1999).…”

Resposta de duas cultivares de arroz irrigado à densidade de semeadura e à adubação nitrogenada

“…Wells & Faw (1978) e Singh & Pillai (1996) têm atribuído o aumento do rendimento de grãos em decorrência do incremento da adubação nitrogenada ao aumento do número de grãos formados por panícula. No entanto, Ghobrial (1983) e Reddy et al (1986 também consideraram o aumento do número de panículas por unidade de área como um fator determinante do aumento do rendimento de grãos de arroz com incremento do nível de N aplicado.…”

“…Desta forma, no ano em que a resposta ao N foi menor, quando houve resposta, esta só ocorreu na densidade mais baixa de semeadura. Resultados semelhantes foram obtidos por Wells & Faw (1978).…”

Tillering, Lodging and Yield under Deep Water Treatment in Direct-seeded Rice

“…The proportion of the latter may be increased by the larger and earlier productive tiller production, resulting in the increase in the degree of grain filling. Wells and Faw (1978) also concluded that excessive vegetative growth before anthesis limited grain yield under dense populations. Since the number of non-productive and weaker tillers were reduced by DW, the tillers received more light, accumulated more photosynthates to the panicles, and finally filled the grains more sufficiently under DW.…”