The potentials of multi-nutrient soil extraction with 0.01 M CaCl2 in nutrient management

</hr></strong> Key words: 0.01 M CaCl ₂ , soil testing, nutrient management, decision-making, multi-nutrientAim of this thesis is to improve the understanding of nutrient dynamics in soil and thereby to improve decision-making in nutrient management. There is a need for a more mechanistic approach of decision-making because the classical approaches cannot comply with the tightening up of legislation and boundary conditions for sustainable agricultural production.The thesis encompasses eight separate papers in which the mechanistic backgrounds of the 0.01 M CaCl ₂ soil extraction procedure has been studied as well as the perspectives of the design of a multi-nutrient CaCl ₂ soil testing program. The studies have been focussed on the cations Ca, Mg and K. Although the use of CaCl ₂ as a soil extractant is promising, it is concluded that the design of a multi-nutrient CaCl ₂ soil testing program is time-consuming and costly. A framework for decision-making in nutrient management has been worked out. In this framework the multi-nutrient 0.01 M CaCl ₂ soil extraction procedure is used as a standardized procedure to give a chemical characterization of soils at a pH and ionic strength comparable to field conditions. This characterization is used as input in a soil chemical model to calculate nutrient speciation and nutrient distribution under varying conditions. This nutrient speciation and distribution is used to characterize the pool of plant available soil nutrient. It is proposed to integrate the CaCl ₂ soil extraction procedure with a soil chemical model, a crop growth model, a soil microbiological, a soil hydraulic model and an optimization procedure into a practical tool for nutrient management decision-making. This tool can then be used i) to tune plant nutrient requirements for maximal crop production and crop quality to the magnitude of the pool of plant available soil nutrient in time and space, and ii) to optimize farm activities in order to comply with more and stricter legislation and boundary conditions related to nutrient management. It is concluded that the perspectives of the multi-nutrient CaCl ₂ soil extraction procedure in mechanistic soil nutrient models and in nutrient management are promising