Crop Rotation Effects on Soil Properties and Cotton (Gossypium hirsutum L.) Yield in Semi-Arid Texas
The Southern High Plains (SHP) and Rolling Plains (RP) of Texas are semi-arid regions, residing in the bottom of the Great Plains of the U.S. Due to decreasing aquifer levels, rainfed acreage within the region has increased. On rainfed acres, cropping systems must be designed to capture and store precipitation and enhance resiliency of the system to withstand prolonged drought events. The implementation of a crop rotation within a management system can potentially improve water dynamics, soil chemical, and physical parameters. Other potential benefits include the decrease of insect pressure, weed pressure, and wind erosion. The inclusion of drought hardy alternative crops with the ability to complete biological nitrogen fixation (BNF) have been reported to increase plant available inorganic N and cotton (Gossypium hirsutum L.) lint yield. Guar (Cyamopsis tetragonloba L.), a drought hardy legume with the ability to biologically fix nitrogen (N). Guar is considered a minor crop in the U.S. The main product of guar is galactomannan gum, extracted from the seed endosperm. Galactomannan gum is used in numerous industries ranging from food and fiber to oil and gas. The implementation of guar in management systems in the U.S has been hindered due to access to commercial inoculant, lack of federal crop insurance, and the recent hiatus of the only U.S. based processing plant. However, guar can potentially offer many benefits in a rotation by increasing the availability of inorganic N within the soil, increasing soil organic matter by leftover crop residue, and improving soil water dynamics (Rose et al., 2022). The objective of this study was to evaluate and compare the impact on soil chemical parameters, specifically inorganic N availability, and cotton lint yields when including alternative crops in rotation with cotton to a cotton monoculture. To address these objectives, sites in Lubbock and Chillicothe, TX were selected, and experiments conducted in 2020 through 2022. Two-year crop rotations (cotton (Gossypium hirsutum L.)-cotton, guar-cotton, grain sorghum (Sorghum bicolor L.)-cotton, and guar-grain sorghum), were implemented. Blocks were established within a single agronomic field to collect multiple years of rotation in a short time frame. These short-term crop rotations in 2020 – 2021 increased nitrogen-N (NO3--N) availability at the Chillicothe site at a soil depth of 15-60 cm. In the 15-30 cm depth, systems containing guar had greater available NO3--N compared to the grain sorghum crop rotation. A similar trend was determined at the 30-60 cm depth, with systems containing guar having greater available NO3--N compared to all other crop rotations. The Lubbock site had a similar trend in 2020-2021, at 0-60 cm depth, systems containing guar had greater NO3--N compared to the grain sorghum - cotton crop rotation, respectively. Differences in soil chemical parameters in the second block of the two-year crop rotation at the Chillicothe site were not determined. This study suggests guar in rotation with cotton can increase NO3--N amounts it did not result in an increase of cotton lint yield compared to a cotton monoculture. Therefore, growers could reduce reliance on synthetic fertilizers and potentially decrease inputs. However, further research is required to better evaluate if guar is economically and agronomically sustainable in semi-arid regions.