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, R2 > 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.
","abstract_html":"<p>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 (R<sup>2</sup> > 0.95 for any site year, R<sup>2</sup> > 0.80 for combined site years).</p> <p>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<sup>-1</sup>), and was positively related to the predicted soil K critical value. However, the mechanisms affecting K release/fixation still require more study.</p>","abstract_has_math":false,"creators":["Zhao, Chun"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Dissertation","degree_discipline":"Agronomy","degree_department":null,"school":null,"contributors":["Brad Joern","Jim Camberato","Darrell Schulze","Hao Zhang"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2013,"date_issued":"2013-10-01T07:00:00Z","date_published":"2013-10-01T07:00:00Z","updated_at":"2026-07-24T03:53:22Z","subjects":["biological sciences","nitrogen mineralization","nitrogen modeling","potassium fixation","Soil Science"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://docs.lib.purdue.edu/open_access_dissertations/12","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Brad Joern","Jim Camberato","Darrell Schulze","Hao Zhang"]},{"key":"dc:creator","label":"Author","values":["Zhao, Chun"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"thesis:degree_discipline","label":"Discipline","values":["Agronomy"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["biological sciences","nitrogen mineralization","nitrogen modeling","potassium fixation","Soil Science"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://docs.lib.purdue.edu/open_access_dissertations/12"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["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, R2 > 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.
"]},{"key":"dc:title","label":"Title","values":["Nitrogen and Potassium Dynamics of Selected Indiana Soils"]}]}],"canonical_facts":{"dc:contributor":["Brad Joern","Jim Camberato","Darrell Schulze","Hao Zhang"],"dc:creator":["Zhao, Chun"],"dc:description.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, R2 > 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.
"],"dc:identifier":["https://docs.lib.purdue.edu/open_access_dissertations/12"],"dc:subject":["biological sciences","nitrogen mineralization","nitrogen modeling","potassium fixation","Soil Science"],"dc:title":["Nitrogen and Potassium Dynamics of Selected Indiana Soils"],"thesis:degree_discipline":["Agronomy"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T03:53:22Z"}