Changes in Nutrient Availability

The transition from conventional to organic and low-input farming is accompanied by changes in an array of soil chemical properties and processes that affect soil fertility. Fundamental differences, both qualities and quantitative, in the flow and processing of nutrient result from the use of cover crops, manure and compost applications, and reduction or elimination of synthetic fertilizers and pesticides. These changes affect nutrient availability to crops either directly by contributing to nutrient pools or indirectly by influencing the soil chemical and physical environment. 

There were no measurable changes in plant available nutrients in the soil of the Apelsvoll... 

Neumann, G., and Romheld, V. (2002). Root-induced changes in the availability of nutrients in the rhizosphere. In Plant Roots The Hidden Half, 3rd edition, Waisel, Y., Eshel, A., and Kafkafi, U., eds., Marcel Dekker, New York, pp. 617-649. 

Additionally, changes in nutrient cycling, uptake, and availability have been proposed in conjuncticyi with acidification based on a few carefully controlled studies but the acidification mechanism has not been fully understood. Subtle changes, such as these, which occur over plant generations are difficult to measure and require long term intensive studies for appropriate assessment. 

Satisfactory definitions of nutritional status in PEM are not available. Traditionally, anthropometry has been used to classify young children because growth is such an essential characteristic of health and is sensitive to changes in nutrient balance. Weight, height, skinfold thickness, limb circumference, head circumference, and other measures have been employed as clinically relevant... 

The effects that changes in vegetation have on soil carbon pools and nutrient availability are also difficult to evaluate. However, several models have been successful in predicting vegetation-soil nutrient relationships because they assume that such changes occur as a result of different rates of decomposition and nutrient release from leaf litter of different taxa 50, 60), Such predictions could be tested and the models refined or parameterized for new taxa by measuring soil nutrient availability and respiration in stands of different species on the same soil type. For example, fifty years ago the U.S. Civilian Conservation Corps (CCC) established such stands as species trial plots measurements in some indicate large differences in soil nutrient availability (48), Further measurements in these stands would now occur at the same time-scale at which we expect the feedback between species replacement and soil processes to occur. 

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