Simulating water stresses in sorghum-sudangrass production with different nitrogen sources and tillage systems

Authors: SARKAR, RESHMI - Texas A&M Agrilife; Northup, Brian

Submitted to: Journal of Soil Science and Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2023
Publication Date: 8/24/2023
Citation: Sarkar, R., Northup, B.K. 2023. Simulating water stresses in sorghum-sudangrass production with different nitrogen sources and tillage systems. Journal of Soil Science and Plant Nutrition. 23:5759-5780. https://doi.org/10.1007/s42729-023-01438-6.
DOI: https://doi.org/10.1007/s42729-023-01438-6

Interpretive Summary: Hay production in the Southern Great Plains (SGP) is largely rainfed and relies on moisture from rain and snow to support crop growth. These water sources present a challenge, as weather in the region varies among and during years, with erratic timings of events and amounts received. Annual amounts range from 11 to 60 inches on an east-west axis (eastern New Mexico to eastern Oklahoma), and individual locations in the region can receive annual amounts with a range like the entire region. As such, conserving soil moisture is important to ensure there is enough water to support hay crops, and is the driving force for using fallow periods as part of the management plans for crops. However, fallowing is not overly efficient in conserving soil water. Losses occur by evaporation from the soil surface, in runoff, or in movement to deeper sections of the soil profile. Conservation tillage and growing a crop for cover or a green source of nitrogen (called green manure) during fallow periods are among the tools that can protect the soil surface and make water use by crop systems more efficient. We assessed variations in simulated water-stress for a brown midrib cultivar of sorghum-sudangrass that was grown for hay and examined how two tillage systems (no-till, and conventional till) and three spring-grown (March to May) green manures (oats, field pea, grass pea) affected production compared to a control (spring fallowed with 60 lb. inorganic nitrogen per acre). We used information developed from long-term records (2006 to 2015) of rainfall (March to July) for 3 sites in central Oklahoma, combined with measures of available water in the upper 26 inches of soils and levels of production at the sites (2011 to 2015) to model the performance of sorghum-sudangrass. We applied the collected information to the Decision Support System Agrotechnology Transfer (DSSAT) simulation model to describe hay production by sorghum-sudangrass during May through July and simulate water stress and amount of available soil water during two different summers (2012, drought-affected; 2015, wet conditions). We modified the existing model for grain sorghum to simulate how water in different soil layers changed during the growing seasons. Sorghum-sudangrass produced slightly more hay under no-till across years and types of green manure. Weather during the two years had the greatest influence on growth by sorghum-sudangrass. Green manures improved hay yields (205 to 295 lb/acre/year) under both tillage systems, and tillage systems explained 63% of yearly production. Water stresses on sorghum-sudangrass were affected by type of growing season but not influenced by the different nitrogen treatments. More water was available in subsurface soils across years under conventional tillage for all treatments. No-till provided more water during the wet year, but less during the drought year for treatments including green manures, and the lower amounts were offset by an improved efficiency in water use for the two crops (green manure and sorghum-sudangrass). Overall, using green manures during the spring could be a useful strategy for conserving soil water across tillage systems when producing sorghum-sudangrass for hay.

Technical Abstract: Conserving soil moisture is an important precaution for drought resiliency for crop production in the U.S. Southern Great Plains (SGP). Conservation tillage and cover crops or green manures are tools that can provide cover to protect soils and conserve moisture. We assessed variations in simulated water-stress for sorghum-sudangrass (Sorghum bicolor (L.) Moench x Sorghum sudanense (P.) Stapf.) grown for forage, and examined impacts generated by tillage systems (no-till, NT and conventional, CT) and three spring crops grown as green manures (oats, field pea, grass pea) compared to a control (spring fallow and 60 kg inorganic N ha-1). We used routines within the Decision Support System Agrotechnology Transfer-Crop Simulation Model (DSSAT-CSM) to describe production and agroecosystem function during 2006 to 2015 and predict production, water stress, and available soil water in two contrasting growing seasons (2012, dry; 2015, wet) in central Oklahoma, USA. We modified genotype-specific files and parameters of the ‘Residue’ file to simulate change in available moisture by soil layer. Sorghum-sudangrass produced slightly higher amounts of biomass under NT across years and green manures. Weather variables significantly influenced sorghum-sudangrass during growing seasons. Green manures significantly (P < 0.05) increased biomass production (229 to 328 kg ha-1yr-1) across tillage systems; 63% of production was explained by form of tillage. Water stress on production was affected by growing seasons but not by N treatments. More water was available in subsurface soils (15-30 cm) across years under CT and was more uniform across treatments. Water availability under NT differed among years and varied by treatments within years; green manures reduced available soil moisture and resulted in more efficient use of water. Heatmap analyses for NT systems noted precipitation and predicted soil water were negatively related to solar radiation and daily maximum temperatures. Green manures were an effective strategy for conserving soil moisture across tillage systems, and could be beneficial in use of soil water in sorghum-sudangrass systems.