Late Season Tissue Tests for Critical Grain Protein Content in Durum, Maricopa, 1999
KeywordsAgriculture -- Arizona
Grain -- Arizona
Forage plants -- Arizona
Barley -- Arizona
Wheat -- Arizona
Barley -- Fertilizer management
Wheat -- Fertilizer management
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AbstractProper nutrient management is necessary for successful production of durum wheat in the desert. If grain protein content is less than 13 %, significant economic losses to growers can result. Late season nitrogen (N) fertilization can resolve this problem, but tissue test guidelines have not yet been established. The objectives of this study were to: (i) correlate NO₃-N in dried stem tissue with sap NO₃-N, (ii) determine the minimum NO₃-N concentration in lower stem tissue at heading associated with the critical grain protein content, and (iii) determine whether flag leaf head, or whole plant total N at heading can be used as indicators of N status. In November 1998 three varieties of durum wheat, Mohawk, Kronos, and Westbred 881, were planted at the Maricopa Agricultural Center. Five N rates (0, 100, 200, 300, and 400 lbs/A) were applied in four split applications. Each treatment was replicated three times in a randomized complete block design. Samples were collected from the lower stem, flag leaf head, and whole plant from each plot at heading and analyzed for total N. Grain yields ranged from 1937 to 6174 lbs /A for Mohawk, 1706 to 6161 lbs/A for Kronos, and 864 to 5162 lbs/A for Westbred 881. Grain protein content averaged 5.7% to 14.0% for Mohawk, 7.3% to 13.7% for Kronos, and 7.9% to 14.5% for Westbred 881. Correlation coefficients between stem NO₃-N and sap NO₃-N were 0.88 for Mohawk, 0.94 for Kronos, and 0.98 for Westbred 881. The critical NO₃-N concentration in the sap associated with >13% grain protein was 550 -770 ppm at heading for three varieties. Lower dried stem tissue critical NO₃-N concentration for Kronos was 4500 ppm NO₃-N, 4700 ppm NO₃-N for Mohawk, and 3600 ppm NO₃-N for Westbred 881 for a grain protein content of 13 %. Nitrogen concentration in flag leaves, heads, and whole plants were highly correlated with N rate. Therefore, N concentration in these tissues could potentially be used as indicators of late-season N status.
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