Published on Wednesday, November 02, 2016
One factor that farmers consistently believe to be a yield limiting factor is their nutrient management. How can we best determine nutrients needs that are necessary in our fields? One theory has often been that smaller soil sample grids can better determine the nutrients and management necessary for every acre.
Farmers usually want to variable rate their fields to start the growing season on a level playing field. By better understanding a field and how soil characteristics are distributed, we can efficiently and correctly manage our crops.
When comparing the traditional 2.5 acre-grid sample and the 0.5 acre-grid sample taken in fall of 2015, differences were noted both on the overall maps (images shown below) and the acreage results show in the graphs below. For example, the 0.5 acre-grid soil sampling determined that 12.36 acres had the soil cation exchange capacity (CEC) range of 16 to 20 meq/100g while the 2.5 acre-grid size determined that 16.8 acres were at this same level.
When sampling on the traditional 2.5 acre-grid size, a total of 49.45 acres were determined to be at a soil potassium level between 200 and 300 lb./lb. When using the smaller acre-grid, only 45.45 acres were determined to be at this range. In addition, more acres were listed in the 300 to 350 lb./lb. of potassium at the 0.5 acre-grid sampling size than in the 2.5 acre-grid sampling size. Changes in potassium content of a soil is likely correlated with changes in other nutrients. Our goal is to test on the smallest scale possible while still making it both practical and affordable for farmers.
While comparing recommendations of lime, phosphate, and potash, there are some distinct differences in recommendations based on acre-grid sampling size. In the case of recommended lime applications, the 2.5 acre-grid sample resulted in an average application of 304 lbs./A. This would cost a farmer approximately, $3.38/A. on average.
On the other hand, the 0.5 acre-grid sample resulted in an average of 118 lb./A. of lime applied. This would cost a farmer $1.31/A. It is also clear that in the instance of the 0.5 acre-grid sample, we are being more efficient in our fertilizer application. The areas needing extra lime would receive that application using the smaller grid size sampled. The same was true of potash application. The 2.5 acre-grid sampling recommended an average of 352 lb./A. while the 0.5 acre-grid sampling recommended an average application of 329 lb./A. While the difference in cost for potash will be minor, we do a better job of placing the product using the 0.5 acre-grid sample (shown below).
The phosphorus application recommendations (shown below) also show trends demonstrated by the potash imagery. Recommendations on the 0.5 acre-grid size average 35 lb./A. less than when compared to the hand sampled 2.5 acre-grid size.
After their research determined that sampling on 0.5 acre grids is the most economical approach for farmers, Integrated Ag Services (IAS) has developed an automated Precision Soil Sampler that is designed to sample on 0.5 acre grids. This system has removed the possibility of sampler error as the instrument consistently takes a 30-foot vertical slice to a depth of 7 in. every 150 ft. The question of equipment failure also comes into play. Fortunately, the precision soil sampler has three cameras focused on the equipment which allows the operator to watch the sampler for any errors or malfunctions. This system has soil samples paired with both GPS points and bar codes in order to track samples collected and be more efficient. You can learn more by watching the video below.
Author: Alex Knight
Categories: PFR, PFR Reports
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