James Adkins, Extension Irrigation Engineer, adkins@udel.edu
Evapotranspiration minus precipitation in inches. (April 5-April 19, 2023)
Wheat
The unusually warm spring and lack of rainfall has depleted our soil moisture levels to the point that small grains should be irrigated to prevent limiting vegetative growth. The map above shows the 2-week evapotranspiration rate minus any precipitation received over the same period. Keep in mind the ¾ of the of the moisture deficit accrued just this week. The current moisture deficit values in Sussex are currently below the TOTAL moisture holding capacity of loamy sand soils causing significant plant stress.
A UD study conducted in 2013-2015 showed the critical time to irrigate wheat was just before flowering with little economic return outside of the that period. However, none of the study years were subjected to the significant early dry spell we are currently experiencing. The average cost to apply 1 acre inch ($4/acre*in) is currently $1.83 less than the July contract wheat price so a 1 bushel increase in yield will more than cover the cost of 2 – 1/2“ irrigation applications. If we do not receive any appreciable rainfall out of Saturdays forecast, pivots should be running immediately.
Barley
I am unaware of any regional data to support the irrigation of barley, however those with malting and high value contracts should consider irrigating similarly to wheat. Barley tends to be more drought tolerant than wheat, but we are quickly approaching critical levels that barring rainfall this weekend will need irrigating soon.
Cover Crops
Much like small grains, vetch and clover are starting to suffer from lack of moisture particularly in sandy soils. While irrigating legumes has the potential to increase the total nitrogen fixed the effect of moisture levels on nitrogen credit is unquantified. The current price of commercial nitrogen does not justify irrigation of covers solely for the N credit.