Part II of this series briefly discusses developing a question and selecting a site for an on-farm study. Prior management and field properties are key to site selection. Keeping the study simple is equally important for collecting meaningful data. Research projects are designed to identify or validate answers to questions or ‘hypotheses’. The example used in part II of this series dealt with answering the question; ‘What is the optimal starter phosphorus (P) fertilizer rate for corn in this field?’. Answering this question requires that strips of starter fertilizer rates of 0, 25, 50, and 100 lbs P2O5/acre be placed in the field, but what do we measure?.
Before selecting the site, review the soil test P values for the field. Fields with upper medium (>10 Olsen P) to very high (>16 Olsen P) are not good candidates for this experiment, low soil test P (<8 Olsen P) are more suitable. Although a soil test may be available from the previous year, measurement of soil test P will be necessary. Fields where manure has been applied after the last soil test should be avoided. Collect samples from various parts of the test strips in a manner to measure how much soil test P varies across the field. Each sample point should be marked with a global positioning system (GPS) but a physical marker is also recommended.
The most important measurement is yield. Yield monitors make this easy but careful attention to details is still a must; shifting rows during harvest ‘contaminates’ the yield measurement. In the end when all measurements have been taken, these data can be used to develop a series of ‘yield response curves’ that can be used for economic optimization. Figure 1 provides a conceptual model of how measured data is used to develop these curves. Yield increases with soil nutrient supply and then levels-off, graphs to the right demonstrate how these curves may look when nutrient levels are A) low, B) medium, and C) high. Data collected in the example experiment could be used to develop these curves for varying zones of productivity across the field, optimizing for profit. More information about yield response curves and economic optimization is available in Reitsma et. al.,2011 or Murell and Bruulsema, 2008. The data’s journey from collection to developing useful information requires statistical analysis but these analyses are made easy with today’s technology. More discussion of on-farm research will follow. If you have any questions; assistance is available from SDSU Extension Service by contacting Kurt Reitsma Precision Farming Specialist, Sioux Falls Regional Extension Center (605) 782-3290 or Dr. C. Gregg Carlson, SDSU Plant Science Department, Brookings, (605) 688-4761.
Additional Information:
Murrell, T.S. and T.W. Bruulsema. 2008 Principles of Allocating Funds Across Nutrients. Better Crops 92:3-5. International Plant Nutrition Institute, Norcross GA. Available at http://www.ipni.net/ppiweb/bcrops.nsf/$webindex/72325B8B263419F4852574AA006E1BB3/$file/BC08-3p03.pdf.
Reitsma, K.D., D.E. Clay, and C.G. Carlson. 2011. Soil Fertility. In D. Deneke (ed). Alternative Practices for Agronomic Nutrient and Pest Management for South Dakota. South Dakota State University, South Dakota State University Extension Service, Brookings SD.