Many cropping decisions based on soil type

I live and work just east of I-95 in the central part of North Carolina. The soil varies from deep coarse sand with clay more than 30 inches to the top of the ground, to sandy loam with the clay 8-10 inches down.

The first soil mentioned is very unproductive for most crops, while the latter is very productive.

Many times I have the same answer for a lot of completely different questions. The answer is, it depends on the soil. Here are some of the questions, with answers.

• Can I put out my potash in March for corn soybeans, and cotton?

On the deep sand, no. Potash on these soils is easily leached. They have low cation exchange capacity (ability to hold fertilizers that have a positive charge), plus deep clay. The clay can hold leached potash, but needs to be within reach of the roots for the plants to get it.

When clay is greater than 30 inches the volume of roots in this zone is small, and potash uptake from here is limited. These soils need potash applied as close to planting as possible. In fact it is better to apply the potash 3-4 weeks after planting. You escape 3-4 weeks of leaching.

On good soils with a finer texture and the clay closer to the top of the ground, potash can be applied in March. These soils hold potash well, and may not even need potash if the potash index is greater than 75 on the NCDA soil sample sheet.

• How many pounds of nitrogen does my cotton need?

Fifty to 100 pounds is a normal rate. On deep sands 80-100 pounds is usually okay, however, even more may be needed depending on leaching.

On the good soils 70-80 is usually okay. If soybeans have been the previous crop for the last two years or more, approximately 20 pounds less than this should be applied.

If you do the math on this the nitrogen rate is 50-100 pounds as mentioned. This is an extreme range rate.

• Do I need to treat fields with a nematicide that are classed as a “B” category (this means you might need to treat) from the NCDA nematode lab?

Again it depends on the soil. On good soils you probably do not need to treat. On poor soils you probably do, especially for root knot. Nematode populations build much more rapidly and to higher numbers on these soils. The crop is also much more likely to encounter drought conditions on poor soil, so it needs a very good root system.

The list goes on. Soil insect pressure, nitrogen rate on other crops, deep-tillage needs, etc. It is the most important circumstance of farming.

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