Research Accomplishments (pdf)
Nutrient and Water Management, Plant Nutrition, Water Quality
Developed best management practices of pre-plant and in-season nitrogen fertilization of potatoes in the Pacific Northwest for production of maximum yield of high quality processed tubers. These new recommendations take into account the contribution of soil residual nitrogen for crop requirement, and minimizing the leaching losses by careful monitoring of soil water content as basis for improved irrigation scheduling.
Developed estimates of nitrogen transformation and availability from crop residues in a typical potato rotation system in the Pacific Northwest. Understanding this component of nitrogen availability is particularly important as the potato cropping practices change to include a variety of cover crops and reduced tillage in order to minimize soil degradation.
Provided clear guidelines to include improved irrigation management as an important step towards improving nutrient management to minimize nitrate leaching losses. Demonstrated the application of real time soil water monitoring as basis to improve irrigation scheduling to minimize leaching of water and nutrients below the rootzone.
Developed the components of citrus tree nitrogen budget to fine tune the nitrogen management recommendations and developed precision irrigation scheduling on the basis of continuous monitoring of soil moisture content in an effort to minimize leaching losses of water and nutrients below the rootzone without adversely impacting the production and net returns.
Demonstrated the beneficial effects of adaptation of new nutrient and irrigation best management recommendations for citrus production in sandy soils as evident from improvement of water quality by decreasing the nitrate_nitrogen concentration in the surficial aquifer without adverse impact on citrus fruit yield and fruit quality.
Developed techniques to increase the accuracy of evaluation of copper phytotoxicity by using the root copper concentration as an index of severity of phytotoxicity and developed citrus production recommendations to minimize copper phytotoxicity in high copper soils with an improved understanding of different forms of copper in soils with long term, high copper loading.
Demonstrated the beneficial effects of application of gypsum or phosphogypsum for crop production in sandy soils, and for amelioration of acid soil infertility factors and discovered the mechanisms of gypsum or phosphogypsum induced amelioration of acid soil infertility factors as influenced by variable vs. permanent charge characteristics of the soils.
Using plant growth studies, solution speciation models, and size exclusion chromatography techniques, made the following classic contributions to the theory and practices of managing the acid soil infertility factors:
Discovered that monomeric aluminum species as the toxic forms of aluminum in solution and that the presence of excess concentrations of either phosphorus, sulfate, or fluoride decreased the phytotoxic forms of aluminum in solution.
Demonstrated that an increased concentration of calcium and/or silicon in solution decreased the aluminum phytotoxicity as a result of physiological effect which provided increased tolerance to high concentrations of aluminum in the root environment.
Identified outer sphere complexation of aluminum with sulfate as a mechanism of providing a shielding effect on toxic form of aluminum for decreasing its phytotoxicity.
He has been sought after to mentor numerous graduate students and post docs, and to host visiting scientists in his laboratory. He has served in several editorial capacities and has been invited to present papers internationally. He has been frequently consulted by producer groups and regulatory agencies on various issues related to impact of agricultural production on the water quality and development of management practices to mitigate such impacts.
Presented over 150 invitational and volunteer papers and seminars at international, national, and statewide meetings, and was invited to give guest lectures in Brazil, Germany, Denmark, Israel, India, and China. He was invited to serve as a co-editor of Florida State Horticultural Society proceedings (1995-1998) and serves as technical reviewer for 13 peer-reviewed journals.
Co-edited three books, and authored or co-authored 19 book chapters, 240 refereed papers, 120 non-refereed papers, and 130 abstracts of the voluntary papers presented at international, national, and regional professional meetings.