| dc.description.abstract | Guar (Cyamopsis tetragonoloba L.), a source of forage, vegetable, and green manure, and a crop whose gum has various industrial applications, is normally grown in semi-arid regions worldwide. It is hypothesized that guar, as a legume, could provide many ecosystem service benefits when integrated into monocrop cereal systems like winter wheat. The objectives of this study were to: i) determine optimum planting dates for guar, and ii) explore the ecosystem services that could be gained from the integration of guar into the wheat monocrop systems. To achieve the objectives of this study, a recently developed guar module (CROPGRO-Guar) and an existing wheat module (CERES-Wheat) in the Decision Support System for Agrotechnology Transfer (DSSAT) Cropping System Model were utilized. Both modules were calibrated and evaluated for rainfed conditions using measured data from 2019 to 2021 growing seasons at Chillicothe in the TRP region. With the evaluated model, long-term seasonal and sequential simulations were run for the period of 30 years (1990-2019). The optimum planting dates for guar were determined based on guar grain yield and crop water productivity (CWP). A planting date window from April 7 to July 19 was found to be favorable for achieving higher guar yields. However, a planting date window of June 13-19 was found to be optimum for achieving higher guar crop yield and CWP. The identified optimum planting date windows varied greatly when accounting for climate variability. For warm conditions, spring planting dates (late March to late April) were favorable for achieving higher yields whereas summer date window (late May to mid-June) was found to be optimal for warm and normal conditions. The ecosystem services resulting from integration of guar into wheat monocrop systems were also identified by comparing simulated results from the guar-wheat rotation treatments with the results from monocrop treatments (guar and wheat). The compared results included yield, soil nitrogen, crop nitrogen uptake, and CWP. The results showed that the integration of guar into wheat systems could slightly decrease wheat grain yield and CWP by about 15% and 2.4%, respectively. Simulated changes in supporting ecosystem services included a 23% increase in soil nitrogen and fixing of about 74.5 kg/ha of nitrogen. Regulating services such as reduction in runoff and related soil and nitrogen losses by about 83% were also simulated. Results from this study provide useful recommendations to enhance ecosystem services of winter wheat cropping systems of the TRP region. | |
