Improved Nitrogen Management in Irrigated Durum Wheat Using Stem Nitrate Analysis: I. Nitrate Uptake Dynamics
- T.C. Knowles,
- T.A. Doerge and
- M.J. Ottman
Intensive N management for irrigated spring wheat (Triticum aestivum L.) grown in arid and semi-arid regions requires preplant soil, plus periodic basal stem analyses for nitrate. Additional information on the relationships between grain yield and quality, N rates and stem nitrate-N (NO3-N) levels is needed for the wide range of agronomic conditions found in areas where irrigated durum wheat (Triticum turgidum L. var. durum) is grown. Five field experiments were conducted during the 1985 to 1988 crop years in southern Arizona to examine the effects of N rate, mobility of N fertilizer form, level of residual soil N, soil texture, and two contrasting wheat cultivars on basal stem NO3-N concentrations and grain yield and quality of durum wheat. Stem NO3-N concentrations were responsive to both fertilizer and soil-N levels. Nitrogen applications containing mobile NO3-N or urea-N resulted in stem NO3-N concentrations at the Feekes 2 growth stage (GS) that averaged 52% less (2.0 vs. 4.2 g NO3-N kg−1) than when an equivalent amount of an immobile NH4-N source was used on Casa Grande sandy loam (coarse, loamy, mixed (calcareous), hyperthermic, Typic Natrargid (reclaimed)] soil. Different N sources had no significant effect on stem NO3 levels for wheat grown on a Trix clay loam [fine loamy, mixed (calcareous), hyperthermic, Typic Torrifluvent] soil. Wheat grown on finer textured clay loam soils showed a two fold increase for NO3-N accumulation in basal stem tissue due to N applications ranging from 225 to 651 kg N ha−1 over the sampling period from GS 6 through 10.5. No statistical or practical differences were observed in the quantities of NO3-N contained in the stem tissue of two popular durum wheat cultivars (Aldura and Westbred-881) when equivalent rates of N were applied. Visual deficiency symptoms were not observed, and subsequent grain yield and quality did not suffer when stem NO3-N levels decreased to no lower than 1.0 g kg−1 following GS 6. These results provide important information needed to increase the precision and accuracy of the basal stem tissue NO3-N test for predicting the N status of irrigated durum wheat.
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