The Last Irrigation for Wheat and Barley - April 2001

The Last Irrigation for Wheat and Barley

Mike Ottman, Extension Agronomist, University of Arizona, Tucson

The timing of the last irrigation for wheat and barley is always a difficult decision. Applying an irrigation that is not needed wastes water and can cause lodging. Conversely, water stress at the end of the season may reduce kernel weight, test weight, and yield. Certain growers apply a final irrigation to add moisture to the soil and promote easier tillage after harvest. Some crops have late tillers which complicates the decision of whether or not to apply a final irrigation.

Knowledge of water use during the various phases of grain fill can help with the decision of whether or not to apply the last irrigation (Table 1). About 3 to 4 inches of water is needed to carry the crop from soft dough to maturity. The average sandy loam soil holds about this amount of plant available water in the active rooting zone. Therefore, on a sandy loam soil, the last irrigation is needed at soft dough. On lighter soils, the last irrigation may be needed between soft dough and hard dough, and on heavier soils, the last irrigation may be applied before soft dough. Obviously, the timing of last irrigation depends on soil type, the irrigation system, the time of year, the variety, the growth stage of the crop, and other factors. Nevertheless, no irrigation water is needed once the heads have completely turned color from green to brown since the crop is mature at this point and yields have been made. Do not confuse the gradual color change of the crop during grain fill as the awns and leaf tips turn brown with the brown color of the head that occurs at maturity.

Table 1. Typical water use pattern for wheat and barley planted in mid-December at Maricopa for the interval from flowering to the end of the hard dough stage (maturity).

Stage¹	Description of Stage	Days at stage²	Days from Flowering	Daily water use (inches)	Water use during stage (inches)	Water use to maturity (inches)
Flowering	Pollen shed	6	6	0.33	2.0	10.0
Water	Kernel watery	7	13	0.31	2.2	8.0
Milk	Kernel milky	8	21	0.30	2.4	5.8
Soft dough	Kernel mealy or doughy	9	30	0.28	2.5	3.4
Hard dough	Kernel stiff dough and turning color	6	36	0.15	0.9	0.9

¹ Stage: Flowering occurs 1-2 days after heading in barley and 7-10 days after heading of wheat and durum. Maturity occurs at the end of the hard dough stage when the heads have completely turned color from green to brown, and fluid does not glisten on a cut kernel when squeezed. The kernels are harvest ripe about 10 days after maturity.

² Days at stage: The interval between flowering and the end of hard dough could be longer with earlier planting or cooler weather, shorter with later planting or warmer weather, can vary among varieties by as much as 6 days, and water use would be affected accordingly.

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

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