Approaches to valuing regional responses in plant productivity from investment in natural resource management are reviewed. The usefulness of data from surveys for estimating marginal physical product is discussed. Since investment reduces declining trends in productivity, an estimate of value marginal product based on based on milk price has seemed appropriate. But as forage is an increasingly substitutable intermediate product in dairy production systems its value will not exceed that of the least cost substitute. Qualified estimates indicate the extent of overestimation of benefits produced by some previous approaches. Implications for natural resource management policy are considered.