EFFECTS OF FERTILIZER N AND SOIL MOISTURE ON GROWTH, N CONTENT, AND MOISTURE USE BY SPRING WHEAT

Abstract

The accumulation of dry matter and N in wheat (T. aestivum L. cv. Manitou) grown on stubble land in lysimeters at two moisture levels and seven rates of N was measured and related to moisture use at five stages of development. In the irrigated lysimeters, leaf areas, plant dry matter and N content increased with fertilizer N. In the dry lysimeters, low rainfall between the shot blade and anthesis stages produced moisture stress; consequently, dry matter production and leaf area were depressed and plants lost significant amounts of N at rates of N > 61.5 kg/ha. Rain in the latter part of the growing season permitted the plants to recover and by maturity plant dry matter and N content increased with N. Approximately twice as much plant dry matter was produced in the wet treatment as in the dry for all levels of N. Total evapotranspiration (ET) increased with applied N in the wet treatment, and was much higher than in the dry treatment. It was not affected by applied N in the dry lysimeters. Root weight increased exponentially up to the shot blade stage. Between anthesis and maturity, it decreased in the top 75 cm in the dry and top 30 cm in the irrigated soil profile, while in the deeper segments it remained constant. Root weight increased curvilinearly with increasing N under irrigation. On dryland, rates of N > 41 kg/ha depressed root growth at the shot blade stage and at anthesis. Average root yields under wet conditions were 220, 1,920 and 1,425 kg/ha at 3-leaf, anthesis, and maturity, respectively; under dry conditions they were 220, 1,535 and 875 kg/ha. The root weight constituted 76% of the total plant weight at the 3-leaf stage and 15.6% at maturity. The average root N content at maturity made up 9.4–11.5% of the mean plant N. Root density decreased curvilinearly with depth. At the 3-leaf stage about 62 and 23% of the root system was located in the top 15- and the 15- to 30-cm segments of the profile, respectively; at maturity these proportions were 46 and 15%. N did not influence root distribution but irrigation increased root growth in the top 15 cm of the profile by about 5%. Rate of moisture use was directly proportional to rate of root growth.