Soybean Irrigation Management

By Younsuk Dong and Lyndon Kelley et.al

1. Introduction

Unlike corn, soybeans don’t consistently respond to irrigation— some farmers notice little to no change in yield whether they irrigate or not. This limited response is largely due to a lack  of understanding about how to manage soybean irrigation, as irrigating soybeans differ significantly from that of corn.

One of the main reasons soybeans haven’t responded to irrigation as effectively as corn is that they’ve been irrigated in the same way. Soybeans grown in Michigan have a different growth habit than corn. Soybeans are classified as having   an “indeterminate” growth habit, meaning vegetative growth continues after flowering. Vegetative growth also impacts nutrient uptake, which denotes soybeans’ tendency to have more of a season-long nutrient assimilation matching biomass production. In contrast, corn has a “determinant” growth habit, where vegetative growth stops as tasseling and ear formation begin. Unlike soybeans, corn tends to have a  period  of  rapid nutrient uptake just prior to the R1 growth stage. This fundamental difference in growth patterns helps explain why corn and soybeans often respond differently to irrigation.

2. Water Requirement by Growth Stage

To determine the timing and rate of irrigation water needed, understanding how the soybean plant grows in relation to its water needs during the season is important. The stage designation and descriptions are presented in Table 1. Total water used by soybeans during a growing season is about 18”–20”, compared to 20”–22” for corn. Water use by the soybean plant varies as the plant grows from emergence to maturity. Figure 1 shows the average water use of a soybean plant at various growth stages.