Relating Soil Test Nutrient Trends to Production Practices.

Soil testing is a long-used nutrient management tool in many cropping systems. However, growers generally utilize soil test recommendations for the immediate growing season and usually do not use them along with crop yields and fertilization practices to evaluate long-term trends in soil nutrient status. A case study will be discussed which includes over 20 years of soil test and production information for corn on an active production farm. One example includes the “crop down” of P from a previously heavily manured field from an initial high of 72 ppm Bray #1-P to recent levels of 9 ppm. Other examples include regression analysis of soil test P and K levels as they decline in spite of applying these nutrients at recommended levels. The effects of increasing crop yields due to high levels of management in relation to soil test information will also be discussed. These techniques can be useful in developing nutrient management plans in corn-soybean production systems.