EFFECT OF TEMPERATURE, NITROGEN FERTILIZATION AND MOISTURE STRESS ON GROWTH, ASSIMILATE DISTRIBUTION AND MOISTURE USE BY MANITOU SPRING WHEAT

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Abstract
The effects of early moisture stress [tillering (Tg) to last leaf visible (LLV)], late moisture stress [LLV to anthesis (AN)], and three rates of N fertilizer (44, 88 and 132 kg N/ha) on the development and moisture use characteristics of spring wheat (Triticum aestivum L. ’Manitou’) were determined under simulated irrigation in the growth chamber at day/night temperatures of 27 °C/12 °C (T27/12) and 22 °C/12 °C (T22/12). Plant height was unaffected by N and by early stress, but was reduced by late stress. Number of tillers increased until LLV, then decreased sharply and remained constant to maturity. More tillers were initiated at T27/12 than at T22/12, but by maturity there was little difference. Leaf blade photosynthetic area reached its maximum at LLV, while the non-leaf blade photosynthetic area reached its maximum at AN and constituted 75% of the total photosynthetic area at the milk dough stage. Heads comprised no more than 9% of the photosynthetic area at any time. Total plant matter accumulated sigmoidally, but at T27/12 and low N rates, plants lost total dry weight after the milk dough stage. Dry matter of the vegetative plant parts increased until the milk dough stage, then stems in particular, and roots to a lesser extent, lost weight. Head weight increased linearly at about 17.5 mg/head/day. Dry matter accumulation was directly proportional to N applied, inversely related to temperature, temporarily retarded by early stress and markedly reduced by late stress. Although stems were the dominant vegetative dry matter sink, leaves were the dominant N sink. A combination of high temperature, high N and moisture stress resulted in a temporary loss of N from the plants between LLV and the milk dough stage. As maturation proceeded, N assimilates appeared to move from leaves to roots into stems and thence into heads. The average rate of N accumulation in the heads was 0.22 and 0.27 mg/head/day at T22/12 and T27/12, respectively. Some N was lost by denitrification. The amount and rate of evapotranspiration were directly proportional to N applied and in general inversely related to moisture stress. The rate of moisture use was generally more rapid at T27/12, but the amount used was no different from that at T22/12. Plants stressed early recovered and used water at the same rate as unstressed plants, but plants stressed late did not recover.

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