Field-Scale Comparison of Seven Soil Sampling Designs for Nutrient Recommendations. Patrick Buckwalter

Transcription

1 Field-Scale Comparison of Seven Soil Sampling Designs for Nutrient Recommendations Patrick Buckwalter

2 Site-specific Management n Some form of precision agriculture has been implemented on many farms n Advances in GPS and GIS technology and variable-rate (VRT) application capability have made adoption of site-specific management much easier n New technology is available to growers n VRT application is readily available from many input suppliers

3 Soil Sampling n Still a wide range of sampling designs in use in the Midwest n Traditionally universities recommended a sampling by soil type and topography but areas not larger than 5 to 10 acres n Recently ISU also began recommending grid sampling (pub PM 287) n A 2.5-acre grid-sampling pattern and VRT for P, K and lime is becoming the industry standard

4 n Questions: This Study n Is the 2.5-acre grid pattern adequate for estimating field variability in soil nutrients? n Is a denser sampling design needed to better describe soil-test variability and can it be costeffective? n How much error in fertilizer prescriptions arises from extrapolating data over large areas?

5 Study Field in Dodge County, Minnesota

6 Soil Types Legend Code Soil Description Acres % of Field Productivity Index M506B Kasson silt loam, 1-6% slopes M518B Clyde-Floyd complex, 1-4% slopes M511A Readlyn silt loam, 1-3% slopes N522A Otter silt loam, 0-2% slopes, frequently flooded

7 Soil-sampling Designs n Sampled the field for P, K, and ph using seven different sampling patterns n Grid-samples n 0.5-acre n 1-acre n 2.5-acre n Block designs n 10-acre n 20-acre n 5-acre n 10-acre

8 Sampling Methods n For grid designs n Sampled 6 depth n cores per sample n Sampled from center point, area approximately 50 sq. ft. n For block designs n Sampled 6 depth n cores per sample n Sampled randomly from within entire block area

9 0.5-Acre Grid

10 1-Acre Grid

11 2.5-Acre Grid

12 5-Acre Grid

13 10-Acre Grid

14 10-Acre Blocks

15 20-Acre Blocks

16 This Study n Calculated descriptive statistics of soil-test results for the field n Calculated frequency of soil-test results in ISU interpretation categories n From the soil-test results nutrient application prescriptions were generated using ISU fertilizer and lime recommendations n A cost analysis was calculated the total cost of each design including sampling, testing, cost of fertilizer or lime and application charges

17 Results

18 Soil-test Phosphorous Results 0.5-acre grid Interpretation Class Bray-P1 ppm VL 0-8 L 9-15 M H VH acre grid 2.5-acre grid 5-acre grid 10-acre grid 10-acre blocks 20-acre blocks

19 Soil-test Potassium Results 0.5-acre grid Interpretation Class K ppm VL 0-90 L M H VH acre grid 2.5-acre grid 5-acre grid 10-acre grid 10-acre blocks 20-acre blocks

20 Soil-test ph Results 0.5-acre grid Interpretation Class ph acre grid 2.5-acre grid 5-acre grid 10-acre grid 10-acre blocks 20-acre blocks

21 Summary statistics for soil-test results for the study field. Soil Test Design N Mean Median Min Max Range SD CV ppm % Bray-P1 0.5 ac grid ac grid ac grid ac grid ac grid ac block ac block K 0.5 ac grid ac grid ac grid ac grid ac grid ac block ac block ph 0.5 ac grid ac grid ac grid ac grid ac grid ac block ac block N, number of samples; SD, standard deviation; CV, coefficient of variation.

22 Frequency Distribution of Soil-test P by Design Number of samples in each category 60 Frequency Acre 1 Acre 2.5 Acre 5 Acre 10 Acre (G) 10 Acre (B) 20 Acre (B) 0 VL L M H VH Soil Test Category

23 Frequency Distribution of Soil-test K by Design Number of samples in each category Frequency Acre 1 Acre 2.5 Acre 5 Acre 10 Acre (G) 10 Acre (B) 20 Acre (B) 0 VL L M H VH Soil Test Category

24 Frequency Distribution of Soil ph by Design Frequency Distribution for ph by Sampling Design 35 Number of Samples Acre 1 Acre 2.5 Acre 5 Acre 10 Acre (G) 10 Acre (B) 20 Acre (B) ph Category

25 This Study n Questions: n Is the 2.5-acre grid pattern adequate for estimating field variability in soil nutrients? n Is a denser sampling design needed to better describe soil-test variability and can it be costeffective? n How much error in fertilizer prescriptions arises from extrapolating data over large areas?

26 P Fertilizer Recommendations Fertilizing recommendations used to generate phosphorous (MAP) application prescriptions for each sampling design. Soil-test Class Corn Soybean Total Total MAP Recommendation used (MAP) lb P 2 O 5 /acre lb/acre VL L M H VH Recommendations are for two crops, beginning with corn in 2011 and soybean in One lb/acre was used for the High testing category to maintain distinct categories on application maps.

27 K Fertilizer Recommendations Fertilizing recommendations used to generate potassium (Potash) application prescriptions for each sampling design. Soil-test Class Corn Soybean Total Total Potash Recommendation used (Potash) lb K 2 O/acre lb/acre VL L M H VH Recommendations are for two crops, beginning with corn in 2011 and soybean in One lb/acre was used for the High testing category to maintain distinct categories on application maps.

28 Lime Recommendations Recommendations used to generate lime application rates for each sampling design. Interpretation Class ph Lime Application -----Tons/acre These are custom rates currently in use on a number of farms in SE MN.

29 MAP Application Maps Interpretation Class Bray-P1 ppm Application (lbs/acre) VL L M acre grid H VH acre grid 2.5-acre grid 5-acre grid 10-acre grid 10-acre blocks 20-acre blocks

30 Potash Application Maps 0.5-acre grid Interpretation Class K ppm Application (lbs/acre) VL L M H VH acre grid 2.5-acre grid 5-acre grid 10-acre grid 10-acre blocks 20-acre blocks

31 Lime Application Maps 0.5-acre grid ph Lime (tons/acre) acre grid 2.5-acre grid 5-acre grid 10-acre grid 10-acre blocks 20-acre blocks

32 Cost of Products and Services Prices used for calculating cost of fertilizer applications. Product or Service Price Units MAP $ Ton Potash $ Ton Lime (applied) $14.00 Ton Dry Application (VRT) $7.50 Acre Lab Fees $6.67 Sample The lab fees are actual costs from Midwest Labs, Omaha, NE. The price of products and application are quotes from Farm Country Co-op, Pine Island, MN.

33 Cost Analysis for Phosphorous Cost analysis for phosphorous Grid Grid Grid Grid Grid Block Block Category 0.5 Acre 1 Acre 2.5 Acre 5 Acre 10 Acre 10 Acre 20 Acre Tot lbs MAP 9,256 8,229 11,592 6,862 10,160 12,864 12,480 Lbs/acre MAP $/acre MAP Sampling cost Lab Fees $/acre VRT $/acre Total $/acre P $93.48 $67.95 $74.65 $45.85 $59.16 $72.27 $69.20

34 Total Cost Analysis Total cost for soil sampling, laboratory fees, fertilizer, lime, and application costs. Grid Grid Grid Grid Grid Block Block Category 0.5 Acre 1 Acre 2.5 Acre 5 Acre 10 Acre 10 Acre 20 Acre $/acre MAP $/acre Potash $/acre Lime Sampling cost Lab Fees $/acre VRT /acre Total $ $ $ $ $ $ $151.83

35 Cost Components by Design Total Cost of Each Sampling Design and Components Total Cost ($/acre) VRT application Lab Fees Sampling cost Lime Potash MAP Acre 1 Acre 2.5 Acre 5 Acre 10 Acre (G) 10 Acre (B) 20 Acre (B) Sampling Design

36 Cost Comparison by Design for High, Medium and Low Fertilizer Price Scenarios Cost of Sampling Designs Fertilizer Price Scenarios Cost per Acre Low Medium High Acre 1 Acre 2.5 Acre 5 Acre 10 Acre (G) 10 Acre (B) 20 Acre (B) Sampling Designs

37 Fertilizer Prices for Low, Medium and High Scenarios Definition of fertilizer costs for Low, Medium and High fertilizer price scenarios. Low Medium High $/ton MAP $/ton Potash $/ton Lime

38 This Study n Questions: n Is the 2.5-acre grid pattern adequate for estimating field variability in soil nutrients? n Is a denser sampling design needed to better describe soil-test variability and can it be costeffective? n How much error in fertilizer prescriptions arises from extrapolating data over large areas?

39 Comparison of large-scale sampling designs to the densest design for the land area in each P interpretation class. For each design the acreage of the study field in each interpretation class is compared to the same class in the 0.5 acre grid design P Interpretation Class VL L M H VH 0.5 ac grid ac grid Difference % Change ac grid Difference % Change ac grid Difference % Change ac grid Difference % Change ac conv Difference % Change ac conv Difference % Change Values in red font are errors of greater than 50%.

40 Comparison of large-scale sampling designs to the densest design for the land area in each K interpretation class. For each design the acreage of the study field in each interpretation class is compared to the same class in the 0.5 acre grid design K Interpretation Class VL L M H VH 0.5 ac grid ac grid Difference % Change ac grid Difference % Change ac grid Difference % Change ac grid Difference % Change ac block Difference % Change ac block Difference % Change Values in red font are errors of greater than 50%.

41 Comparison of large-scale sampling designs to the densest design for the land area in each ph interpretation class. For each design the acreage of the study field in each interpretation class is compared to the same class in the 0.5 acre grid design ph Interpretation Class ac grid ac grid Difference % change ac grid Difference % change ac grid Difference % change ac grid Difference % change ac conv Difference % change ac conv Difference % change Values in red font are errors of greater than 50%.

42 This Study n Questions: n Is the 2.5-acre grid pattern adequate for estimating field variability in soil nutrients? n Is a denser sampling design needed to better describe soil-test variability and can it be costeffective? n How much error in fertilizer prescriptions arises from extrapolating data over large areas?

43 Conclusions n A 1-acre grid pattern was slightly less ($8/acre) expensive than a 2.5-acre grid, and captured more field variability (greater range of values) n In this uniform field, denser patterns resulted in reduced fertilizer usage n Large block patterns resulted in over-application of nutrients and were not less expensive n Dense grids resulted in fewer application errors n Better assessments of cost/benefits should include measurements of actual crop responses, which were beyond the scope of this study

44 Thank You! n Dr. Antonio Mallarino, Iowa State University n Dr. Richard Cruse, Dr. Ken Moore, Iowa State University n Virgil K. Webster Scholarship Committee n Jeff Newman, Farm Country Co-Op n John Menghini, Midwest Laboratories n Jesse Drew, Tom Schultz, Dawn Miller and Jaci Severson, Iowa State University