1. Spatial Variability in Precision Agriculture What is it? What is it? – Precision n. The quality or state of being precise. Used or intended for precise measurement. Used or intended for precise measurement. Made for the least variation from a set standard. (Webster, 1995) Made for the least variation from a set standard. (Webster, 1995) – Precise adj. Capable of, caused by, or designating an action, performance, or process carried out or successively repeated within close specified limits (Webster, 1995). What is it? What is it? – Precision n. The quality or state of being precise. Used or intended for precise measurement. Used or intended for precise measurement. Made for the least variation from a set standard. (Webster, 1995) Made for the least variation from a set standard. (Webster, 1995) – Precise adj. Capable of, caused by, or designating an action, performance, or process carried out or successively repeated within close specified limits (Webster, 1995).

2. Precision Agriculture What is it? What is it? – Precision in management? – Knowing more precisely the size of fields, size of fields, level of inputs (rates), level of inputs (rates), yields, yields, $ costs, and $ costs, and $ returns? $ returns? What is it? What is it? – Precision in management? – Knowing more precisely the size of fields, size of fields, level of inputs (rates), level of inputs (rates), yields, yields, $ costs, and $ costs, and $ returns? $ returns?

3. Precision Agriculture What is it? What is it? – Management of production inputs in relation to more precisely delineated needs (Johnson, 1/18/01). Recognizes spatial variability of production needs within a population of production units, where production units are smaller than they used to be. Recognizes spatial variability of production needs within a population of production units, where production units are smaller than they used to be. What is it? What is it? – Management of production inputs in relation to more precisely delineated needs (Johnson, 1/18/01). Recognizes spatial variability of production needs within a population of production units, where production units are smaller than they used to be. Recognizes spatial variability of production needs within a population of production units, where production units are smaller than they used to be.

4. Spatial variability among production units. What is the size of a production unit? Depends on the enterprise. – Small dairy = single dairy animal. – Wagoner Ranch, TX = 7,000 – 8,000 acre wheat field. Agronomic units = “fields” What is the size of a production unit? Depends on the enterprise. – Small dairy = single dairy animal. – Wagoner Ranch, TX = 7,000 – 8,000 acre wheat field. Agronomic units = “fields”

5. Spatial variability among production units. What causes field delineation. – Natural boundaries. Rivers Rock out-crops – Political boundaries. Roads Survey units – Land ownership Consolidation What causes field delineation. – Natural boundaries. Rivers Rock out-crops – Political boundaries. Roads Survey units – Land ownership Consolidation

6. Spatial variability among production units. What causes field delineation. – Soil productivity appropriate to the crop (e.g. bottom land for alfalfa). – Size determined by land use Government acreage restrictions (CRP) Tees, fairways, greens – Size that is “convenient” to the operation for administering production inputs. Cultivation Planting Harvesting (mowing) Fertilizing Irrigation Etc. What causes field delineation. – Soil productivity appropriate to the crop (e.g. bottom land for alfalfa). – Size determined by land use Government acreage restrictions (CRP) Tees, fairways, greens – Size that is “convenient” to the operation for administering production inputs. Cultivation Planting Harvesting (mowing) Fertilizing Irrigation Etc.

7. Spatial variability (macro) for agronomic land use. Inherent (natural). – Related to soil productivity and soil forming factors Time Parent material Climate Vegetation Slope Inherent (natural). – Related to soil productivity and soil forming factors Time Parent material Climate Vegetation Slope

8. Soil acidity and Oklahoma rainfall Usually acidic Usually not acidic

9. Spatial variability (macro) for agronomic land use. Acquired (use induced). Influence of historical crop production on soil properties. –Alfalfa vs. wheat for acidification and soil organic matter. –Fertilizer use and change in soil fertility (Garfield County). Acquired (use induced). Influence of historical crop production on soil properties. –Alfalfa vs. wheat for acidification and soil organic matter. –Fertilizer use and change in soil fertility (Garfield County).

10. C.V. = 54; ave = 73 Acquired spatial variability (macro).

11. Garfield Co. Farmer’s Use of Soil Testing and Fertilization PreviousPreviousGrainGrain Normal Fertilization Soil Test Results AcresAcres Soil Test YieldYieldNNPP 22 OO 55 KK 22 OOpHpHNNPPKK SurSurSubSub 86*86*19811981353510010046464.54.524245454106106445445 118*118*19811981252510010046464.94.953531081088888411411 30*30*19891989343410010046465.15.1444443437575377377 65*65*262610010046464.44.4115115118118159159752752 505019811981292910010046465.55.50070704444551551 *Savings from no fertilizer to four fields = 299 acres X $24.50/acre, = $7,325 Cost of not managing acquired spatial variability (macro).

12. Acquired spatial variability (micro). pH=4.9 BI = 6.6 N = 10 P = 93 K = 435 Bottom pH=5.2 BI = 7.0 N = 13 P = 54 K = 354 Terrace 1 pH=5.3 BI = 6.9 N = 10 P = 44 K = 415 Terrace 2 pH=5.7 BI = 6.9 N = 20 P = 23 K = 397 Terrace 3 pH=5.4 BI = 6.8 N = 20 P = 31 K = 522 Terrace 4 pH=5.5 BI = 6.7 N = 12 P = 32 K = 423 Terrace 5 pH=4.6 BI = 6.8 N = 16 P = 65 K = 310 Upland pH=7.3 BI = -- N = 67 P = 22 K = 343 “BadSpot” pH=5.2 BI = 6.8 N = 14 P = 49 K = 408 FieldAveragepH=4.6-5.7 BI = 6.6-7.0 N = 10-20 P = 23-93 K = 310-522 FieldRange

13. “Cow Pocks” in wheat pasture Acquired spatial variability (micro).

14. Ave = 47; CV = 30

15. 1x1 (60-acre cell)

16. 6x4 (2.5 acre/cell)

17. 12x8 (0.625 acre/cell)

18. 25x16 (0.15 acre/cell)

19. 50x32 (0.0375 acre/cell)

20. 100x64 (45 yd 2 /cell)

21. 200x127 (11 yd 2 /cell)

22. 472x300 (2 yd 2 /cell)

23. Management Zones A B C

24. Fundamentals of Nutrient Management

25. Plant Growth and Soil Nutrient Supply Relationships Mitscherlich (1909) “…increase in yield of a crop as a result of increasing a single growth factor is proportional to the decrement from the maximum yield obtainable by increasing the particular growth factor.” dy/dx = (A - y) c Law of “diminishing returns” Plant Growth and Soil Nutrient Supply Relationships Mitscherlich (1909) “…increase in yield of a crop as a result of increasing a single growth factor is proportional to the decrement from the maximum yield obtainable by increasing the particular growth factor.” dy/dx = (A - y) c Law of “diminishing returns” x 1 x 2 y2y2 y2y2 y1y1 y1y1 A-y for x 1 and  y 1 Yield (y) Increasing level of growth factor (nutrient, x)

26. Plant Growth and Soil Nutrient Supply Relationships Mitscherlich – Soil deficiency levels could be expressed as a “percent sufficiency” Plant Growth and Soil Nutrient Supply Relationships Mitscherlich – Soil deficiency levels could be expressed as a “percent sufficiency” % of Maximum Yield or “Yield Possibility ” % of Maximum Yield or “Yield Possibility ” Soil Phosphate (P) or Potassium (K) Supply (soil test index) Soil Phosphate (P) or Potassium (K) Supply (soil test index) 100 50 75 104070100

27. Plant Growth and Soil Nutrient Supply Relationships Mitscherlich Soil Test Correlation and Calibration Soil TestPercentFertilizer P IndexSufficiencyP 2 O 5 02580 104560 208040 409020 65 + 100 0 Plant Growth and Soil Nutrient Supply Relationships Mitscherlich Soil Test Correlation and Calibration Soil TestPercentFertilizer P IndexSufficiencyP 2 O 5 02580 104560 208040 409020 65 + 100 0

28. Plant Growth and Soil Nutrient Supply Relationships Bray “…as the mobility of a nutrient in the soil decreases, the amount of that nutrient needed in the soil to produce a maximum yield (the soil nutrient requirement) increases from a value determined by the magnitude of the yield and the optimum percentage composition of the crop, to a constant value.” Plant Growth and Soil Nutrient Supply Relationships Bray “…as the mobility of a nutrient in the soil decreases, the amount of that nutrient needed in the soil to produce a maximum yield (the soil nutrient requirement) increases from a value determined by the magnitude of the yield and the optimum percentage composition of the crop, to a constant value.” % of Maximum Yield or “Yield Possibility ” % of Maximum Yield or “Yield Possibility ” Soil Phosphate (P) or Potassium (K) Supply (soil test index) Soil Phosphate (P) or Potassium (K) Supply (soil test index) 100 50 75 104070100 Bray mobile nutrient

29. Plant Growth and Soil Nutrient Supply Relationships Bray For a nutrient that is 100 % mobile in the soil (NO 3 -N ?) Soil nutrient supply requirement = Yield X % nutrient in tissue (Input requirement = harvest output or removal) Idealized situation would be hydroponics nutrient supplying system (no soil-nutrient interaction) Plant Growth and Soil Nutrient Supply Relationships Bray For a nutrient that is 100 % mobile in the soil (NO 3 -N ?) Soil nutrient supply requirement = Yield X % nutrient in tissue (Input requirement = harvest output or removal) Idealized situation would be hydroponics nutrient supplying system (no soil-nutrient interaction)

30. What Happens to Applied Nitrogen Fertilizer? AMMONIUMFERTILIZERS NITRATENITROGEN SOIL M ICROORGANISMS SOIL REACTIONS AMMONIUMNITROGEN SOIL ORGANIC MATTER

31. What Happens to Applied Nitrogen Fertilizer? AMMONIUMFERTILIZERSAMMONIUMFERTILIZERS NITRATE NITROGEN NITRATE NITROGEN SOIL MICROORGANISMS SOIL MICROORGANISMS SOIL REACTIONS AMMONIUM NITROGEN AMMONIUM NITROGEN SOIL ORGANIC MATTER SOIL ORGANIC MATTER CROP UPTAKE NH 3

32. Plant Growth and Soil Nutrient Supply Relationships Wheat response to fertilizer N Bray mobile nutrient

33. Plant Growth and Soil Nutrient Supply Relationships Bray Plant Growth and Soil Nutrient Supply Relationships Bray Soil nutrient supply requirement = Yield X % nutrient in tissue Soil nutrient supply requirement = Yield X % nutrient in tissue Bushel Wheat Requirement = (lb/bu) * % N = 60 * 2.2 % N (13 % C.P.) = 1.33 lb N/bushel Assumes –100 % efficiency in converting soil N to wheat grain N. – relatively constant N content At 70 % efficiency, requirement is 1.33/.70 = 1.9 lb N/bu Bushel Wheat Requirement = (lb/bu) * % N = 60 * 2.2 % N (13 % C.P.) = 1.33 lb N/bushel Assumes –100 % efficiency in converting soil N to wheat grain N. – relatively constant N content At 70 % efficiency, requirement is 1.33/.70 = 1.9 lb N/bu

34. Plant Growth and Soil Nutrient Supply Relationships Bray Plant Growth and Soil Nutrient Supply Relationships Bray Bushel Wheat Requirement = (lb/bu) * % N = 60 * 2.2 % N (13 % C.P.) = 1.33 lb N/bushel At 70 % efficiency and 13 % C.P., requirement is 1.33/.70 = 1.9 lb N/bu At 50 % efficiency and 15 % C.P., requirement is 1.53/.50 = 3.1 lb N/bu At 100 % efficiency and 11 % C.P., requirement is 1.1/1 = 1.1 lb N/bu Bushel Wheat Requirement = (lb/bu) * % N = 60 * 2.2 % N (13 % C.P.) = 1.33 lb N/bushel At 70 % efficiency and 13 % C.P., requirement is 1.33/.70 = 1.9 lb N/bu At 50 % efficiency and 15 % C.P., requirement is 1.53/.50 = 3.1 lb N/bu At 100 % efficiency and 11 % C.P., requirement is 1.1/1 = 1.1 lb N/bu

35. Fate of Inorganic N in Soils

36. Nitrogen soil availability Source and fate of nitrate (NO 3 - ). NO 3 - Rainfall LeachingLeaching O 2 + NH 4 + NitrificationNitrification H + + DenitrificationDenitrification N 2 O and N 2 - O 2

37. Rainfall LeachingLeaching NO 3 - DenitrificationDenitrification N 2 O and N 2 - O 2 NO 3 - Nitrogen soil availability Source and fate of ammonium (NH 4 + ). CEC (-) NH 4 + Soil Organic Matter-N Matter-N MineralizationMineralization + OH - + NH 3 + H 2 O H + + NO 3 - O2 +O2 +O2 +O2 + O2 +O2 +O2 +O2 + VolatilizationVolatilization

38. Rainfall LeachingLeaching DenitrificationDenitrification N 2 O and N 2 - O 2 NO 3 - Nitrogen soil availability Source and fate of ammonium (NH 4 + ) CEC (-) MineralizationMineralization + OH - + NH 3 + H 2 O H + + O2 +O2 +O2 +O2 + O2 +O2 +O2 +O2 + VolatilizationVolatilization Soil Organic Matter-N Matter-N NH 3 NO 3 - NH 4 + immobilizationimmobilization

39. Plant Growth and Soil Nutrient Supply Relationships Bray –Current Oklahoma field practice Plant Growth and Soil Nutrient Supply Relationships Bray –Current Oklahoma field practice Estimated yield in bu/acre (YG) * 2 lb N/bu = Estimated N requirement Estimated N requirement - soil test NO 3 -N = Fertilizer N requirement. Estimated topdress N = est.(Yield * %N) - preplant and soil N supplied –sensor based goal Estimated topdress N =k sensed yield and sensed % N Estimated yield in bu/acre (YG) * 2 lb N/bu = Estimated N requirement Estimated N requirement - soil test NO 3 -N = Fertilizer N requirement. Estimated topdress N = est.(Yield * %N) - preplant and soil N supplied –sensor based goal Estimated topdress N =k sensed yield and sensed % N

40. Plant Growth and Soil Nutrient Supply Relationships N use efficiency = [100 (N x - N 0 ) grain N] / N x applied