James Adkins, Extension Engineer, adkins@udel.edu
Inquiries about irrigating soybeans to increase grain moisture began in earnest last week and have accelerated as the forecast continues to be precipitation free. Can you use irrigation to add moisture to 9-10% soybeans to avoid the weight and harvest losses? The short answer is yes, but it’s tricky and an inexact science. In a 65 bu/a soybean crop, 3.1 bu/a of water weight will be sacrificed at 9% moisture versus the ideal 13% in addition to the estimated 2-3 bu/a of shatter loss from being overly dry. Other benefits include dust reduction and the subsequent reduction in fire risk.
How to get moisture back into the bean using irrigation is where things can get tricky. It only takes 22 gallons of water to bring 65 bu/a of 9% beans to 13%. A typical center pivot can’t apply less than 0.2 inches per application or 5,430 gal/acre. To get that moisture into the bean, the water must first soak the pod and remain soaked until that water can be absorbed by the bean. In the current low humidity and moderate wind environment, a daytime irrigation is unlikely to keep the pod wet for long enough to get enough moisture transfer to the bean. If possible, irrigate at the lowest rate possible starting at dusk to increase soak time and wait roughly 18 hours from the start of irrigation to begin harvest. If you have a yield monitor with a calibrated moisture sensor start on the most recently irrigated end of the field and cut towards the irrigation start point. If the moisture at the start of the pass is around 15% and drops to 11% by the end of the pass you will net a 13% average moisture. Keep in mind that the stems will likely be tougher requiring more fuel and your moisture will drop fast as the day progresses. Delmarva farmers who have tried this and similar re-wetting strategies have reported success in increasing bean moisture and reducing shatter losses with one farmer commenting, “The dust reduction alone was worth the cost of the application”.