How Much Potash Should I Apply for Soybeans?

Potassium Requirements

• The crop requires large amounts of potassium for high yields. The plant utilizes the nutrient during the vegetative growth stages and tends to slow during seed formation stage. The potassium requirement in soybeans is determined from soil tests. Soil with very low levels of potassium require 60 to 80 lbs. per acre, soils with low levels require 40 to 60 lbs. per acre, soils with medium levels require 20 to 40 lbs., and soils with high levels need up to 20 lbs. per acre, as recommended by the Kansas State University Extension.

Importance of Potassium

• The nutrient fixes more than 60 sixty different enzyme systems including the one that helps fix atmospheric nitrogen for plant use. Potassium is required for photosynthesis and carbohydrate production. Optimal levels of carbohydrate help in the growth of new root hairs and node development and function.

Potassium Deficiency Symptoms

• The most pronounced potassium deficiency symptom in soybean plants is a distinct yellowing or chlorosis along the margins of the foliage. Older leaves are affected most and first. Chlorosis is followed by browning or necrosis of the yellowed area. Ensure the soil contains the right levels of potassium before planting and growth. Once deficiency and symptoms occur in growing plants, the damage cannot be reversed.

Factors Affecting Potassium Absorption

• A number of factors reduce availability of potassium to plants despite its presence in the soil. Despite considerable potassium in soil, only 1 to 2 percent of it is actually available to plants. Potassium uptake is affected by cold temperature under which the rate of diffusion and root growth is decreased. Plants growing in compacted and poorly aerated soils also have problems in absorbing potassium. Dry soil slows potassium diffusion, making it less available to plants. Sandy soils have problems retaining potassium due to low content of organic matter and clay and hence require more frequent applications of potassium.