Customized Soil Sampling


 

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Recap: Customized Soil Sampling
     

  

Harold Lambert
Lambert Agricultural Consulting, Inc.
Ventress, La.


As cotton harvest winds down, or even before then, I try to begin thinking about the next year’s crop. My clients are much better at this than I am, and since they are strongly devoted to crop rotation, I usually get a tentative crop mix and field plan from them early in the fall.

If possible, I usually do soil fertility and nematode sampling in the fall, giving priority to fields or situations where I have observed or suspected a soil fertility or nematode issue during the previous growing season. Almost by default, most of my attention is on the lighter textured soils. Root-knot nematode is an increasing problem in my area, and we have had to adjust our choice of in-furrow at planting material to protect cotton yield potential.

Regarding fertility, our light, sandy fields or areas within larger fields warrant extra sampling as we struggle with the effects of low organic matter. Rotation and minimum tillage have helped, but we wish we were closer to a source of poultry manure as it could probably be a benefit to some of our problem spots. In general, our very productive light soils will commonly show a need for sulfur, zinc and, occasionally, boron.

Phosphorus and potassium fertilizer rates are also determined by analyses, but I have found that consistently high-yielding fields share a common trait: they soil test high in phosphorus. So, for fields with excellent yield histories that are low in cation exchange and organic matter, I try to be mindful of removal rates when making rate recommendations in order to keep such fields high-producing. Lastly, liming is a reality for us (as per soil test), and I have found that the corn/wheat-soybean/cotton rotation will hasten the need for lime on our light and mixed soils.

We have done some soil EC mapping (with my Veris cart) here in the past and have found that appropriate and beneficial use of such technology is possible in certain situations where there is sufficient soil variability to justify one of the following: 1. Variable rate (VR) nitrogen for cotton using the deep soil EC in order to avoid over applying nitrogen and the problems that causes, 2. VR-Telone applications where nematode levels and damage potential vary according to soil texture – both shallow and deep – and 3. Soil texture variability triggers the need for varying lime rates across a field, but this level of variability is fairly rare.

 

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