Nitrogen and Irrigation Water Interactions in Drought-Stressed Kentucky Bluegrass.

There is increasing pressure in arid regions to conserve water, especially during drought cycles. Turfgrass is the irrigated crop of greatest acreage in the United States and is coming under scrutiny in urban ecosystems. The purpose of this study is to evaluate Kentucky bluegrass (Poa pratensis L.) under various irrigation and nitrogen (N) regimes. A study was conducted in an environmentally controlled growth chamber with established Kentucky bluegrass. The grass was grown in pots with a depth of 11 cm in calcined clay rooting media. The two moisture regimes were 60 or 100% evapotranspiration (ET) daily replacement values with three N regimes of deficient, optimal, and excessive. Average daily ET was 7.1 mm for the fully irrigated treatment, with 4.3 mm for the limited irrigation treatment. The N rates were 48.8, 146.5, and 439.6 kg ha¹ for the deficient, optimum, and excessive treatments, respectively. Nitrogen application was applied in the form of 50% urea and 50% polymer coated urea For the fully irrigated grass, the excessive N resulted in 14% greater water use and the deficient N had 12% less compared to the optimum N. For the drought stressed plants, excessive N resulted in 9.6% greater water use and deficient N 18% less water use. These results indicate that N management influences ET in Kentucky bluegrass. Reducing N can result in water conservation, but the effects on turf health and appearance must be considered. NDVI readings for the fully irrigated turfgrass increased linearly with increasing N rate with values 0.637, 0.694, and 0.725 for deficient, optimum, and excessive N, respectively. The same trend occurred with the drought stressed plants with values of 0.621, 0.662, and 0.698 for deficient, optimum, and excessive N, respectively. The results suggest that water conservation might be achieved by optimizing the interaction of N and water supply. In one case, limiting N may reduce ET of fully irrigated grass. In another case, high N may help maintain green grass when water supply is limited.