Reasons for Uneven Soybean Plant Height

Planting Mistakes

• Planting soybeans too early in the season could slow germination. Soybeans could emerge as quickly as six days after sowing, but extra shade and deep planting could delay emergence by a month. Early in the season, the colder temperatures at deeper levels of the soil interfere with the bean's ability to pull nutrients from the ground. Seeds planted deeper grow more slowly than seeds planted at the optimum depth -- between 1 and 1 1/2 inches, according to North Dakota State University Extension. Waiting for soil temperatures at that depth to reach 50 degrees Fahrenheit gives a more uniform stand.

Pests

• Stunted soybean plants at any stage of growth could signal an attack by pests. Emerging soybeans depend on the store of nourishment in seed leaves or cotyledons for fast early growth. Slugs could damage either the cotyledons or the point of new growth between them. Slugs often kill soybean seedlings growing in wet ground or in thick debris, but slight damage could only set young plants back temporarily. Later in the season, soybean rootknot nematodes could kill feeder roots, causing knots of scar tissue to form on maturing plants. The trochanter mealybug also feeds on the plant's root system. Either problem could create stunted soybeans with yellowing leaves.

Poor Drainage

• Poor drainage in part of the soybean planting could stunt the plants in that section. Plant roots need constant moisture, but waterlogged ground deprives roots of oxygen and suffocates the plants. A slight dip in a level field or garden could trap rain or irrigation water if the subsoil consists of heavy clay. For proper drainage in clay soil, a field needs a slope of at least 0.1 percent, according to MSUCares.com. Planting on a mounded row helps minor drainage problems. Keeping drainage channels clear of debris ensures that no water stands in the garden.

Acid Soil

• High-nitrogen chemical fertilizers increase the acidity of soils over the years and runoff concentrates fertilizer salts in pockets within fields and gardens. Soybeans need soil pH of 6.2 to 6.5 for best growth. Acidic fertilizer pockets could stunt soybeans and other crops. Spot soil tests, taken the fall before planting soybeans, reveal any pH problems. Ask your county extension agent for advice if your soil falls outside the optimum range and till amendments such as agricultural lime or wood ash into the ground to sweeten acidic soil. Broadcasting lime without tilling could take years to correct acid problems, says Croplan Genetics.