Evaluation of Water and Nitrogen Stress on Bromegrass Growth1

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Abstract
Percent stress [reduction in growth rate of bromegrass (Bromus inermis L.) due to deficiency] was calculated by the method of Greenwood et al. to evaluate the effects of deficiencies of N, water, and N plus water combined. Dry matter yields of bromegrass receiving either (a) 270 kg/ha of N, (b) complete irrigation, (c) N plus irrigation, or (d) no treatment 3 weeks earlier were determined at periodic intervals in the field at low, medium, and relatively high levels of N availability. Percent stress due to N deficiency was greatest where N availability was lowest, generally increased as the grass approached maturity, but was insignificant as long as a relatively large pool of inorganic N remained in the soil. Percent stress due to water deficiency was affected by precipitation, and was generally greatest for plots low in available N, even though soil water content (to 120 cm depth) was greater in those plots. Generally, percent stress due to deficiencies of water and N combined was approximately equal to the sum of stresses for the two measured separately. The concept of percent stress appears to be useful for quantifying the effects of both N and water deficiencies, alone and in combination, on growth rates of grass. In connection with other measures of physiological condition or activity, this concept may have considerable utility in agronomic research.

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