EFFECT OF NITROGEN, TEMPERATURE, GROWTH STAGE AND DURATION OF MOISTURE STRESS ON YIELD COMPONENTS AND PROTEIN CONTENT OF MANITOU SPRING WHEAT

Abstract

Manitou spring wheat (Triticum aestivum L.) was grown at combinations of three day/night temperatures (27/12 °C, 22/12 °C and 17/12 °C), three levels of fertilizer nitrogen (58, 116 and 174 kg N/ha), and three moisture stresses, nominally −0.3, −15 and −40 bars. All plants were initially grown at −0.3 bars; one moisture treatment was carried through to maturity at this water potential while the remainder were stressed at −15 or −40 bars from either (i) four-tiller, (ii) boot, or (iii) late flowering stage, to maturity. Under the conditions of this experiment, temperature was the most important factor affecting yield and protein, and moisture stress the least important. Yields were equal at 17 and 22 °C, but greater than at 27 °C. Protein was equal at 17 and 22 °C and less than at 27 °C. Yield increased with nitrogen fertility except at the highest temperature or when high moisture stress was applied from the boot stage. Plants grown under high moisture stress through the boot stage (i.e., stressed from tillering or boot) gave yield increases when fertilized with 116 kg N/ha, but 174 kg N/ha depressed yield of plants stressed from boot stage to maturity. Yields of plants stressed from tillering were generally greater than yields of plants stressed from boot stage, indicating that the plant has the ability to adapt to early stress. In contrast to findings in a simulated irrigation study, moisture stress during the boot stage depressed rather than enhanced seed set. Optimal temperature for spikelet development was near 22 °C. The growth stage most critical to the determination of number of seeds developed was boot stage and that for kernel weight was at or after anthesis. The effect of temperature or protein was independent of nitrogen or moisture level. High moisture stress during boot stage increased protein even at the lowest nitrogen level, but stress from late flowering rarely increased protein. The effect of nitrogen on protein was mainly direct while temperature and moisture acted mainly by influencing yield. The direct effect of nitrogen on protein was twice as great as temperature effect and 15 times that of moisture.