Wednesday, July 29, 2009

Yellow Soybeans and Soil Compaction

Image 1: Yellow soybeans in this field are the result of sidewall compaction.

The spring rush of planting is catching up to the soybean crop in some fields. Surface compaction and sidewall compaction was most likely caused by planting when fields were a little too wet. The compacted soil has restricted root growth on soybeans. Until now, there has been enough water to keep most nutrients within the root zone and the soybeans looked fine. As the soybeans reach full pod development (R4) the plants are rapidly accumulating nitrogen and potassium. The restricted roots are not taking up enough nutrients to sustain plant growth. Plants turn yellow.

Planting all fields in perfect conditions is impossible most springs and especially this one. Timely rainfall now will help move nutrients into the root zone. Yield losses from compaction could be very minor or very sever, depending on rainfall, soil fertility within the root zone and severity of compaction.

Fertilizers at this point will likely have little impact on yields. The soil scientists will address this in more detail.

As more soybeans across Kentucky get closer to full pod and beginning seed development, I expect we will see more yellow soybeans.

Image 2: Soybean roots restricted by sidewall compaction. Root growth is limited mostly to the furrow created during planting.

Image 3: Soybean roots restricted by compaction just beneath the soil surface. Root growth is bending to curve around the compaction. The overall root mass is reduced from the compaction.

Image 4: Soybean roots with little to no restriction. The whole plants are greener and larger. Root mass is greater and there are more nodules per plant.

Image 5: Yellow soybeans have roots with restricted growth while the greener soybeans have little to no restriction on root growth.

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