The availability of water and nitrogen to plant roots are very important factors determining the yield of crops. In soil these two factors are closely linked as nitrogen is chiefly available to crops as nitrate that is very soluble in water. Thereforeenvironmental monitoring of both soil water and nitrate availability is important for crop production with reduced inputs. Progress in this area is limited by the lack of methods for in situ estimates of nitrogen status, soil strength and water availability in the field. In this paper we describe approaches to measure these soil variables in the field environment. We describe the development of sensors to measure soil matric potential between 0 to -300 kPa. An explanation of how these data can be usedwith soil water content data to estimate soil strength is presented. In other research, flexible N-sensors suitable for monitoring soil mineral nitrogen have been developed. These probes have been produced using a new type of nitrate-selective electrodethat has been successfully used in rivers and drainage waters for environmental monitoring. The information obtained from the electrodes can be used to provide diagnostic decision support for fertiliser recommendations and for more general field monitoring by fanners.
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