YIELD OF BROMEGRASS AND REMOVAL OF NITROGEN, PHOSPHORUS AND POTASSIUM UNDER MODIFIED SOIL-TEMPERATURE FIELD CONDITIONS

Abstract

In a 3-year field experiment with bromegrass grown under low moisture stress (< 2 atm), total herbage yield from unfertilized plots was reduced by 39% when the average seasonal soil temperature (14.1 C at a 50-cm depth) was lowered and maintained at 9.2 C; the yield was increased by 71% when the seasonal temperature was raised and maintained at 25.4 C. This represents a change in yield of 6.8% per 1 C change in the seasonal soil temperature, or a Q10 of 1.3 at 9.2 C. Herbage grown on the warm soils continued throughout the season until fall, but growth on the cool soils was negligible after the first harvest in June. Addition of N, P and K to the soil in the spring reduced the effect of a change in soil temperature on herbage yield (3.7% per 1 C). The amount of the yield increase, however, was similar at all three soil temperatures. In contrast to the effect on herbage yield, root accumulation was much greater in the cool soil (30.7 metric tons per ha, 0 to 30 cm depth) than in the seasonal soil (22.7 MT/ha) or in the warm soil (12.1 MT/ha). An increase in concentration of the major nutrients (N, P, K) in the plants coincided with the greater herbage growth on the warm soil. The changes in uptake for N, P and K per 1 C change of the seasonal temperature were 8.7, 10.4 and 7.1%, respectively, and the associated Q10 values were 1.5, 1.6 and 1.4 at 9.2 C. After growing bromegrass for three years, the amount of NO3-N mineralized for subsequent crops was low in soil from the cool plots but much higher in soil from the warm plots. The relative amounts mineralized varied with incubation conditions.