Soybeans are highly tolerant to excess moisture and require 16–20 inches of water for maximum yield potential.1 Sandy, drought-prone soils or inadequate precipitation can reduce soybean yield due to this high water demand. In heavy clay soils, soil compaction or crusting can reduce emergence.
Soybeans and other pulse crops are relatively intolerant to saline soil. Select fields with soluble salt levels <1.0 mmho/cm and avoid soybean production on fields with ≥2.0 mmho/cm.2
Iron deficiency chlorosis (IDC)
Manitoba soils contain adequate amounts of iron (Fe) to meet the demands of soybeans. However, some environmental conditions can reduce the availability and uptake of Fe by the soybean plant, leading to the condition known as Iron Deficiency Chlorosis (IDC).
Conditions that can lead to IDC include excess moisture, salinity, carbonates and/or high nitrate levels in the soil. Symptoms of IDC include yellowing of new soybean leaves between the veins (interveinal chlorosis), and an overall yellowing of soybean fields, particularly during the early vegetative stages in June.
It is often a temporary condition that resolves itself when soil dries up. Plants that recover by the V5 to V6 stage should experience minimal yield loss.3 However, if symptoms persist for > 1 week, yield loss can occur. There is no effective in-season management option, but it is important to accurately diagnose the problem and adjust management strategies for future years. Visual diagnosis (see right), tissue testing and knowledge of soil characteristics can help you diagnose IDC.
The best management tool is prevention. Soil risk factors outlined in Table 1 can be used to identify fields that are at risk of IDC ahead of the growing season. If fields designated for soybeans are at moderate-high risk of IDC, choose a soybean variety with a good (low) IDC rating.
Varietal reactions to IDC (ratings 1–5) are available in the Soybean Variety Evaluation Guide. Other management practices that can reduce the impact of IDC include improved drainage, heavier seeding rates and practices that reduce soil N levels (cover cropping, N management in other crops). Iron chelate products applied in-furrow can reduce IDC; however, however, susceptible soybean varieties may still result in yield loss.3
1 Licht, M., D. Wright and A. Lenssen. 2013. Soybean response to drought. Agriculture and Environment Extension Publications. 190. lib.dr.iastate.edu
2 Franzen, D. 2013. Managing saline soils in North Dakota. NDSU Extension Service. ag.ndsu.edu
3 Goos, R.J. and D. Franzen. How much does IDC reduce soybean yield? NDSU Extension Service. ag.ndsu.edu