Impact of in-season split application of nitrogen on intra-panicle grain dynamics, grain quality and vegetative indices that govern nitrogen use efficiency in sorghum

Authors: OSTMEYER, TROY - Texas Tech University; SOMAYANDA, IMPA - Texas Tech University; Bean, Scott; DHILLON, RAJVEER - Central State University; Hayes, Chad; RITCHIE, GLENN - Texas Tech University; ASEBEDO, ANTONIO - Innovar Ag Llc; Emendack, Yves; JAGADISH, KRISHNA - Texas Tech University

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2023
Publication Date: 9/12/2023
Citation: Ostmeyer, T.J., Somayanda, I.S., Bean, S.R., Dhillon, R., Hayes, C.M., Ritchie, G., Asebedo, A.R., Emendack, Y., Jagadish, K.S. 2023. Impact of in-season split application of nitrogen on intra-panicle grain dynamics, grain quality and vegetative indices that govern nitrogen use efficiency in sorghum. Plant and Soil. https://doi.org/10.1002/jpln.202200325.
DOI: https://doi.org/10.1002/jpln.202200325

Interpretive Summary: Grain sorghum is a semi-arid crop that is well adapted to heat and drought stress conditions. Although sorghum has low nutrient requirements to be productive, greater yields can be achieved with an adequate nitrogen supply. Since most soils lack an adequate supply of nitrogen required for optimal growth of sorghum, external application of nitrogen fertilizer is a common practice. Several studies have investigated the impact of rate and timing of nitrogen fertilization on grain yield in sorghum. However, none of these studies have looked at the effect of a range of combinations of nitrogen rates and in-season split nitrogen applications at critical growth stages on grain yield and and grain protein content as well as variation within the grain head. Therefore, this study aimed to understand the impact of in-season split application of nitrogen on nitrogen use efficiency, grain yield and grain protein content. Our findings indicated that split application of nitrogen played a role in increasing grain protein content but not yield or in nitrogen use efficiency in the tested sorghum hybrid. Selecting sorghum to increase protein content in the seeds at the bottom third of the grain head may be one strategy to improve yield and grain quality in sorghum. Sorghum varieties that move more nitrogen from plant tissues to grains may also improve yield and grain quality. This information will assist in developing sorghum with increased yield and improved grain quality.

Technical Abstract: Determining the impact of in-season split application of nitrogen (N) on grain yield components and quality can help in improving sorghum productivity. A popular grain sorghum hybrid (Pioneer 86P20) for the High Plains region of the US was used to determine optimum rate and timing of N to relate vegetative indices that govern nitrogen use efficiency and, to maximize grain yield and quality under different soil types. Pioneer 86P20 was grown in three environments over two years, and on two different soil types following a completely randomized block design with nine N application treatments. Treatments included differing N rates applied at critical stages of sorghum (planting, panicle initiation, and booting), accompanied with high temporal aerial phenotyping. Opportunities to increase grain protein content while using a split N application was observed, with panicle initiation identified as a critical stage. Vegetative indices i.e., NDVI and NDRE have the capability of predicting grain yield and protein content, respectively. Intra-panicle grain number and weight were altered significantly at different portions within panicles, with bottom portion presenting an opportunity to enhance yield potential. The strong stay-green trait in this hybrid locked a large proportion of nitrogen in the leaves even at maturity, which warrants the need for balancing stay-green and senescence in sorghum improvement programs. These findings highlight the sustainable characteristics of grain sorghum, wherein remobilization of residual N accumulated within the leaves into grain are a target to increase yield and grain quality. An optimized stay-green trait balanced with senescence is recommended for enhancing sorghum yield potential.