Interactive effects of water and nitrogen stresses on carbon and water vapor exchange of corn canopies

Abstract

Water and nitrogen stresses often reduce the yield of corn ( Zea mays L.). Crop responses to low soil nitrogen are similar in many ways to crop responses to soil water deficits. Interaction between nitrogen and water stresses is also common. The objective of this study was to examine the interactive effects of water and nitrogen stresses on canopy photosynthesis, evapotranspiration, and water use efficiency of field corn canopies. Corn was grown on a Kendrick fine sand soil (a member of the loamy, siliceous, hyperthermic family of arenic Paleudults) and subjected to three irrigation treatments (optimal, vegetative water stress, and rainfed). Two nitrogen (N) levels were imposed within each irrigation treatment (low, 62 kg ha −1; high, 255 kg ha −1). During the vegetative water stress period, hourly measurements were made of canopy carbon dioxide exchange rate (CER) and canopy evapotranspiration (ET) on the optimal and vegetative water stress treatments in combinations with both N levels. In addition to decreases in ET caused by water stress, the corn canopies exhibited a decrease in ET when subjected to N stress. Part of this decrease was explained by the lower leaf area indexes (LAI) of the low-N canopies. On day 14 of the vegetative water stress, a curvilinear relationship existed between CER and photosynthetic photon flux density (PPFD) for both the irrigated high- and low-N plants although low-N plants exhibited decreased sensitivity to PPFD during midday hours. In contrast, two distinctly different hysteretic loops were obtained for low- and high-N water stress plants. Instantaneous water use efficiency (CER/ET) varied considerably with time of day and treatment combination. We conclude that most of this variation was the result of different vapor pressure dificits (VPD). Canopy CER was linearly related to ET/VPD regardless of N and water stress and the slope of the line ( k′ = 0.024) was in close agreement with the theoretical value predicted by Tanner and Sinclair (1983) for corn.