Soybean is a crop that can remove significant amounts of nutrients per bushel of grain harvested. Because of this, soybeans can respond to starter fertilizer applications on low-testing soils, particularly phosphorus.
K-State guidelines for soybeans include taking a soil test for phosphorus (P), potassium (K), sulfur (S), zinc (Zn), and boron (B). If fertilizer is recommended by soil test results, then fertilizer should either be applied directly to the soybeans or indirectly by increasing fertilizer rates to another crop in the rotation by the amount needed for the soybeans.
The most consistent response to starter fertilizer with soybeans would be on soils very deficient in one of the nutrients listed above, or in very high-yield-potential situations where soils have low or medium fertility levels. Furthermore, starter fertilizer in soybeans can be a good way to complement nutrients that may have been removed by high-yielding crops in the rotation, such as corn and help maintain optimum soil test levels.
Banding fertilizer to the side and below the seed at planting is an efficient application method for soybeans. This method is especially useful in reduced-till or no-till soybeans because P and K have only limited mobility into the soil from surface broadcast applications.
However, with narrow row soybeans, it may not be possible to install fertilizer units for deep banding. In that situation, producers can surface-apply the fertilizer. Fertilizer should not be placed in-furrow in direct seed contact with soybeans because the seed is very sensitive to salt injury.
Soybean seldom responds to nitrogen (N) in the starter fertilizer. However, some research under irrigated, high-yield environments with sandy soils suggests a potential benefit of small amounts of N in starter fertilizer.
Soybean row spacing in Kansas
There are still many questions about row spacing for soybean production. A summary of recent research from K-State, in 2015-17, a series of six On-Farm experiments conducted across eastern and central Kansas. Compared to the conventional 30-inch row spacing, soybeans in narrow rows (15-inch or less) in these tests were likely to show equal or slightly greater yields (2-12%), particularly when the yield environment was less than 50 bushels per acre (regardless of planting date, seeding rate, or maturity). Above this yield threshold level, soybean did not show yield response to changing the row spacing. Overall, the common denominator of the response to row spacing is the inconsistency, denoted by the wide error of responses and by the variability between site-years.
Final considerations - some of the benefits of narrow row spacing:
• Early canopy closure favors better light interception,
• Improved weed control, and reduced potential for soil erosion.
On the other hand, some of the disadvantages of narrow rows:
• Potential reductions in final stand at a given seeding rate, linked to equipment and within row compaction.
• In very dry years, narrow row spacing may consume limited soil water earlier in the growing season, reducing the amount of water available for the critical period around pod-setting and seed filling.
• In wet years, too narrow spacing (less than 15-inch) may allow less air flow within the canopy and favor the occurrence of certain diseases, such as white mold.
Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at email@example.com or call the Hays office, 785-628-9430.