Nitrogen and potassium dynamics of selected Indiana soils

Chun Zhao, Purdue University

Abstract

Nitrogen (N) is the most limiting essential nutrient for crop growth. Numerous studies have been performed to improve N fertilizer recommendations. Accurate prediction of soil N supply has been found to be one of the most important factors that determine optimum fertilizer N rates. Seven soils collected from various locations across Indiana at four different depths were tested for N mineralization potential. Results showed that laboratory mineralizable N in the top layer (0–15 cm) of the seven soils ranged from 50 to 68 mg N kg-1 soil. In addition, more than 50% of the total mineralizable N was contributed from the 15 to 60 cm depths. Different methodologies used for estimating soil N supply capacity were also compared in this study. We found that soil N mineralization estimated from long-term static laboratory incubation was correlated to crop N uptake under greenhouse conditions. Some chemical indices such as Illinois Soil Nitrogen Test, anaerobic-N, and Hot KCl-N also showed promises in predicting laboratory N mineralization potential. However, the mineralizable N estimated from laboratory incubations did not show any relationship with soil N supply in the field, which can be attributed to large weather variations under field conditions. Therefore, a process-based weather-driven N transformation and loss model was developed to improve the prediction of optimum in-season fertilizer N rates. So far through simple regression analyses from existing N response studies we found that yearly plant N uptake simulated from this model was highly correlated to yield data under field conditions (R2 > 0.95 for any site year, R 2 > 0.80 for combined site years). Potassium (K) is also one of the most important essential nutrients for crop growth. The availability of K in the soil determines K fertilizer recommendations. Potassium ions can be fixed between the layers of 2:1 clay minerals in the soil, which decreases the availability of K for plant uptake. We conducted two studies to evaluate the impacts of different factors on soil K availability. One was to assess the effect of anhydrous ammonia (AA) injection on soil K fixation, and the other was to evaluate the effect of soil moisture on soil K test levels. Results of the first study showed that the injection of AA dramatically decreased the nonexchangeable K concentration in some soils up to 4.5 cm away from the injection point, but did not significantly affect the exchangeable K concentration in the soil. In the study about effects of moisture on soil test K (STK) levels, we found that soils with initially high exchangeable K concentrations fixed K upon drying, while soils with initially low exchangeable K concentration released K upon drying. The equilibrium soil K level at which no change in STK occurs upon drying varied with soils (106 to 241 mg kg-1), and was positively related to the predicted soil K critical value. However, the mechanisms affecting K release/fixation still require more study.

Degree

Ph.D.

Advisors

Camberato, Purdue University.

Subject Area

Soil sciences

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