The following comments are based upon the North Carolina Department of Agriculture and Consumer Services (NCDA & CS) summary of soil samples taken in Craven County prior to 2012 crop production. Select data are presented and comments made to aid producers and those planning agricultural production. (To review the complete report, download the NCDA & CS summary at http://www.ncagr.gov/agronomi/sthome.htm).
Abbreviations Used
Phosphorous = P Potassium = K Manganese = Mn Copper = Cu Zinc = Zn
Assumed Crop Production in 2012
Cotton – 7,000 acres Corn – 17,000 acres Peanuts – 8500 acres Sorghum – 1,800 acres Flue-cured Tobacco – 1,920 acres Soybean – 23,500 acres Wheat followed by some other crop = 1, 800 acres Wheat followed by Soybeans = 8,300 acres
Total Production Acres = 61,500 acres
Discussion of Results
The total number of samples taken for field crop production in 2012 was 5,160 samples. If we divide this by the simple average soil sampling size, it shows that approximately 42,000 acres of production, or about 70% of Craven County’s total field crop production, was sampled. Trends showing areas of needed improvement and means to eliminate cost of unprofitable production inputs are outlined below
Obtaining and maintaining target soil pH
- 54% of tobacco fields sampled are not within the desired soil pH target level with 19% of these critically low and 35% between 6.0-6.5.
- 69% of the corn fields sampled are not within the desired soil pH target level with 20% of these either critically low or excessively high.
- 78% of the soybeans fields sampled were not within the desired soil pH target level with 20% of these either critically low or excessively high.
- 19% of the peanut fields sampled were not within the desired soil pH target level with 14% of these critically low.
- 71% of the cotton fields sampled are not within the desired soil pH target level with 20% of these either critically low or excessively high.
Proper soil pH is critical for soil chemical reactions and promotion of a viable biological soil community. Low pH can greatly reduce plant root growth and/or result in aluminum toxicity. Excessively high soil pH (above 6.2) can reduce manganese availability. Improper soil pH can result in poor root growth and/or limit plant nutrient uptake that can lead to yield reductions. This is especially critical if other stresses are present.
Under the assumption that 20% of soils are misrepresented by the data due to high organic matter (lower soil pH target values) and subtracting this 20% value from the listed values for corn, soybeans and cotton crops, approximately 50%-60% of soil pH values are not within the desired soil pH target prior to planting in 2012.
Phosphorous and Potassium Fertilization
Failure to provide either P or K to soils that are low in these nutrients can reduce yield. In contrast, addition of these two plant nutrients when they are not needed simply adds unprofitable cost to production. One exception is that small amounts of P added as a starter (10-20 lbs/ac) have been proven to increase yield and promote early growth for some crops. Thus, it is strongly advised to follow the NCDA & CS recommendation regarding P & K fertilization.
In addition to added costs, excessive P fertilization places farmland at risk for regulatory action and potentially negative environmental impacts. Soils with excessively high P levels should follow NCSU Best Management Practices (BMP) to reduce P usage and reduce off-site movement of P. (Visit the NCSU website, http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-20/ for information regarding nutrient BMP).
The table below outlines the percent of crop soil sample results indicating no positive yield response from the addition of P or K. To reduce cost, these fields should avoid fertilization other than starter fertilizers.
Table 1. Percent of Craven County 2012 NCDA & CS Soil Sample Results with Soil Index Levels Exceeding Levels That Require Additional Phosphorous or Potassium Fertilization
|
CROP |
PERCENT OF SAMPLES WITH HIGH P INDEX VALUES |
PERCENT OF SAMPLES WITH HIGH K INDEX VALUES |
|
Tobacco |
93% |
64% |
|
Corn |
81% |
79% |
|
Soybean |
86% |
65% |
|
Cotton |
87% |
65% |
|
Peanut |
97% |
67% |
Micronutrient Management
Manganese consistently showed a need for better management than other micronutrients. As much as 17% of the samples have a critically low soil Mn index and as much as 35% showed excessive Mn soil index levels. Very high Mn soil levels and low pH can create Mn toxicity. Excessive soil Mn Index levels implies that producers are spending money to apply Mn that is not needed.
Zinc and Copper were more consistent but still concerns are worthy of mention. Low soil zinc levels can reduce crop yield but high zinc levels can be toxic to some crops such as peanuts. Copper is not generally toxic but exceptionally high soil index values suggest the addition of a costly nutrient application that does not add to profitable production.
SPECIFIC CROP SAMPLE DATA SUMMARIES
Soil Samples Listed for Tobacco Production in 2012 Number of Soil Samples = 247 Average Size of Sample = 7.8 acres per sample
Soil pH
- 35% of sample results have a pH value between 6.0-6.5. This value is higher than the target range and may present problems with Mn deficiency or increased disease.
- 19% of samples have a pH value between 0.0 and 5.4. These values are too low and may result in poor root growth, aluminum toxicity and require excessive fertilization.
Soil Phosphorous
- 93% of sample results reveal that no crop yield will result from the addition of P. Phosphorous will aid in early growth and subsequent bloom. However, 5.0 lbs/ac of P in transplant water has been proven to equal 40 lbs/ac of P banded. If this is not feasible, consider banding 10-15 lbs/ac of P to avoid excessive production cost that will not impact profitability while also reducing potential negative environmental impacts.
- Only 6% of the sample results show the potential to increase yield with the addition of P.
Soil Potassium
- 64% of sample results reveal no crop yield will result from the addition of K.
- 3% of the samples results are very low to critical levels of soil K.
Manganese
- 2% of sample results show very low to critical levels of soil Mn.
- 37% of sample results have an excessive soil Mn level.
Soil Samples Listed for Corn Production in 2012 Number of Soil Samples = 2305 Average Size of Sample = 7.4 acres per sample
Soil pH
- 5% of sample results have a soil pH greater than 6.5. This can greatly reduce Mn availability.
- 15% of sample results have a soil pH between 0-4.9. This is critically low and may greatly reduce root growth, result in aluminum toxicity or require excessive fertilization.
- 69% of the samples are below the soil pH of 6.0.
Phosphorous
- 81% of the sample results show that no yield increase can be expected from the addition of P fertilization. However, early growth and potentially early flowering may result from the addition of P. Applications of low P rates in complete banded fertilizer application or as an in-furrow treatment have proven to be sufficient.
- Of the 19% of the sample results that will respond favorably with increased yield potential from P fertilization, only 1% are very low to critical.
Potassium
- 13% of the sample results show that soil K indexes are excessive.
- 2% of the sample results show that soil K indexes are very low.
- 66% of the sample results reveal that no yield increase can be expected from K fertilization.
Manganese
- 15% of the sample results reveal that soil Mn is critically low.
- 81% of the sample results reveal very high to excessive soil Mn levels.
Soil Samples Listed for Soybean in 2012 Number of Soil Samples = 2375 Average Size of Sample = 9.9 acres per sample
Soil pH
- 4% of sample results have a soil pH greater than 6.5. This can greatly reduce Mn availability.
- 14% of sample results have a soil pH between 0-4.9. This is critically low and may greatly reduce root growth, result in aluminum toxicity or require excessive fertilization.
- 78% of the samples are below the soil pH of 6.0
Phosphorous
- 86% of the sample results show that no yield increase can be expected from the addition of P fertilization.
- 2% of the sample results have critically low in soil P Indexes.
- 12% of the sample results show that yield increases may result from the addition of P fertilization.
Potassium
- 2% of the sample results have very low to critical soil K indexes.
- 65% of the sample results reveal that crop yield increase are not likely due to K fertilization.
Phosphorous & Potassium
- 29% of the sample results show that yield will not increase from the addition of either P or K.
Manganese
- 11% of the sample results have critically low in soil Mn Indexes.
- 40% of the sample results reveal very high to excessive soil Mn Indexes.
Soil Samples Listed for Peanut Production in 2012 Number of Soil Samples = 120 Average Size of Sample = 7.0 acres per sample
Soil pH
- 2% of sample results have a soil pH greater than 6.5. This can greatly reduce Mn availability.
- 14% of sample results have a soil pH between 0-4.9. This is critically low and may greatly reduce root growth, result in aluminum toxicity or require excessive fertilization.
- 3% of the samples report a soil pH between 5.0-5.4. Other than organic or mineral-organic soils, this pH range is too low for optimum crop yield.
Phosphorous
- 97% of the sample results show that no yield increase can be expected from the addition of P fertilization.
- 3% of the sample results reveal critically low soil P Indexes.
Potassium
- 67% of the sample results are excessive and may reduce yield and/or peanut quality
Manganese
- 6% of the sample results have critically low soil Mn levels.
- 31% of the sample results have very high to excessive soil Mn levels.
Zinc
- 15% of the sample results reveal an index value above 100. Zinc can be toxic to peanuts at high levels
Soil Samples Listed for Cotton Production in 2012 Number of Soil Samples = 2054 Average Size of Sample = 3.4 acres per sample
Soil pH
- 71% of sample results have a soil pH less than 6.0
- 16% of sample results have a soil pH between 0-4.9. This is critically low and may greatly reduce root growth, result in aluminum toxicity or require excessive fertilization.
- 4% of the samples report a soil pH above 6.5 which may greatly reduce Mn availability
Phosphorous
- 88% of the sample results show that no yield increase can be expected from the addition of P fertilization.
- 53% of the sample results show excessive
Potassium
- 78% of the sample results indicate that yield increase are not to be expected due to K fertilization
- 11% of the sample results have soil K index values listed as excessive
Manganese
- 11% of the sample results are critically low in Mn
- 9% of the sample results are very high to excessive in Mn
- 55% of the sample results reveal that crop yield will not increase with the Mn fertilization
Copper
- 2% of the sample results indicate soil index values that are critically low
Samples listed as Wheat Followed by Soybean Production in 2012 Number of Soil Samples = 849 Average Size of Sample = 9.8 acres per sample
Soil pH
- 71% of sample results have a soil pH less than 6.0
- 21% of sample results have a soil pH between 0-4.9. This is critically low and may greatly reduce root growth.
- 5% of the samples report a soil pH above 6.5 which may greatly reduce Mn availability
Phosphorous
- 88% of the sample results show that no yield increase can be expected from the addition of P fertilization.
- 53% of the sample results have excessive soil P levels.
Potassium
- 78% of the sample results indicate that yield increase are not to be expected from fertilization with K.
- 11% of the sample results have soil K index values listed as excessive.
Manganese
- 14% of the sample results show critically low soil Mn levels.
- 27% of the sample results show very high to excessive soil Mn levels.
- 28% of the sample results reveal that crop yield will not increase from Mn fertilization.
Copper
- 12% of the sample results indicate soil Cu index values as critically low.
- 16% of the sample results indicate soil Cu index values that are excessive.
Samples listed as Wheat Followed by Sorghum Production in 2012 Number of Soil Samples = 266 Average Size of Sample = 6.8 acres per sample
Soil pH
- 78% of sample results have a soil pH less than 6.0
- 9% of sample results have a soil pH above 6.5 which may greatly reduce Mn availability
- 27% of the sample results have a soil pH between 0-4.9. This is critically low and may greatly reduce root growth, result in aluminum toxicity or require excessive fertilization.
Phosphorous
- 86% of the sample results show that no yield increase can be expected from the addition of P fertilization.
- <1% of the sample results have very low or critical soil P levels.
Potassium
- 66% of the sample results indicate that yield increase are not to be expected from K fertilization
- 3% of the sample results have soil K index values listed as excessive.
Manganese
- 11% of the sample results show critically low soil Mn levels.
- 35% of the sample results reveal very high to excessive soil Mn levels.
Zinc
- 23% of the sample results indicate soil Zn index values that are critically low.
Samples listed as Sorghum Production in 2012 Number of Soil Samples = 113 Average Size of Sample = 16.0 acres per sample
Soil pH
- 67% of sample results have a soil pH less than 6.0
- 3% of sample results have a soil pH above 6.5 which may greatly reduce Mn availability.
Phosphorous
- 81% of the sample results show that no yield increase can be expected from the addition of P fertilization.
- <1% of the sample results are very low or critically low in P levels.
Potassium
- 32% of the sample results indicate that yield increase are not to be expected from K fertilization.
- 5% of the sample results have soil K index values listed as very low.
Manganese
- 12% of the sample results are critically low in soil Mn.
- 37% of the sample results reveal very high to excessive soil Mn levels.
