Seeding rate effects on organic rice growth, yield, and economic returns

Authors: LI, XIUFEN - Texas A&M Agrilife; DOU, FUGEN - Texas A&M Agrilife; WATKINS, KENTON - University Of Arkansas; WANG, SHU - Texas A&M Agrilife; CHEN, KUN - University Of Connecticut; ZHOU, XIN-GEN - Texas A&M Agrilife; McClung, Anna; STORLIEN, JOSEPH - College Of St Benedict & St John'S University; HONS, FRANK - Texas A&M Agrilife

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2020
Publication Date: 5/20/2020
Citation: Li, X., Dou, F., Watkins, K.B., Wang, S., Chen, K., Zhou, X., McClung, A.M., Storlien, J.O., Hons, F.M. 2020. Seeding rate effects on organic rice growth, yield, and economic returns. Agronomy Journal. https://doi.org/10.1002/agj2.20304.
DOI: https://doi.org/10.1002/agj2.20304

Interpretive Summary: The demand for organically produced food is the fastest growing sector of the U.S. food industry with an annual increasing rate of over 6 percent. Although the planted area of organic rice in the U.S. has increased from 9,240 hectares in 1995 to 35,102 hectares in 2017, such an increase is still unable to meet the strong market demand. Organically certified crops must meet stringent production requirements which include a prohibition of using non-organic fertilizers and pesticides that are common in conventional rice production. The biggest production constraint in organic rice production is yield losses due to weed pressure. Rice is typically grown in a flooded paddy system which is helpful in controlling some weeds, although other weeds are adapted to aquatic environments. This study was conducted to determine the optimum seeding rate to use in organic rice production systems as a means of decreasing weed pressure and maximizing economic returns. In addition, a representative inbred cultivar, Presidio, and hybrid cultivar, XP753, were used in the study as both are options for organic growers, although the price of hybrid seed is much greater than inbreds and is, thus, a significant economic variable. The study was conducted over two years on land that was certified for organic production and seven seeding rates were used ranging from 108 to 431 viable seed per sq. m. Yield linearly increased with increased seeding rates for both cultivars, with the highest yields obtained at the highest seeding rates. Models were used to determine the economic optimum seeding rate which was 87 kg ha-1 for Presidio and 48 kg ha-1 for XP753. Producers could expect a yield of 3053 kg ha-1 and an economic return of $1288'$1346 ha-1 for Presidio and a yield of 5835'6092 kg ha-1 and an economic return of $1986'$2686 ha-1 for XP753. These results contribute to filling the knowledge gap of how to optimize organic rice production practices and provide a reference to develop improved management strategies.

Technical Abstract: Seeding rate is an important factor in optimizing yield components and thus grain yield of conventional rice (Oryza sativa L.), yet limited information on its effect on organic rice production is available. A field study was conducted under organic management over two years to comprehensively evaluate the effects of seeding rate (108, 161, 215, 269, 323, 376, and 431 seeds m-2) and rice cultivar [Presidio (inbred) and XP753 (hybrid)] on yield components, grain yield, milling quality, weed density, and economic returns. Seeding rate had significant effects on seedling stand density and dry biomass with positive linear correlations. Yield linearly increased with increasing seeding rate with the greatest yields of 3,462 kg ha-1 for Presidio and 7,508 kg ha-1 for XP753 at the highest seeding rate tested. Panicle number was positively correlated with seeding rate, while milling quality was not affected by seeding rate. The linear-plateau (LP) model fit best for Presidio and the quadratic-plateau (QP) model fit best for XP753 to estimate the ex ante economic optimum seeding rate (EOSR). The EOSR was 87 kg ha-1 (340 seeds m-2) for Presidio and 48 kg ha-1 (192 seeds m-2) for XP753. Using the EOSR, producers could expect a yield of 3053 kg ha-1 and an economic return of $1288'$1346 ha-1 for Presidio, and a yield of 5835'6092 kg ha-1 and an economic return of $1986'$2686 ha-1 for XP753.