The ecology of nutrition : managing soil organic matter to supply soil nutrients, increase soil biotic activity and increase crop nutritive value

Abstract

The increasing consumer interest in high quality foods -especially fruits and vegetables with high antioxidant phytochemicals -has led to interest in determining the effects of cropping system practices on phytochemicals over the last decade. Appropriate fertility management is critical to optimize agricultural production, both for yield and crop nutritive value, and minimize losses to the environment. In organic production systems, fertility management generally relies on soil microbial processes to decompose organic matter. To better understand the dynamics of mulch decomposition and the resulting effects on soil fertility and crop yield, a three-year randomized strip-plot experiment was implemented on the Montana State University Horticulture Research Farm. Two mulch inputs with varying carbon to nitrogen ratio (C:N), decomposition rates and microbial responses were contrasted with two non-mulched treatments, urea N fertilizer and a no-treatment control. Spinach biomass, yield, total phenolics and antioxidant capacity were measured as plant response variables to changes in soil fertility and biology due to the different inputs over three years. Water-extractable organic matter (WEOM), available nitrogen (N), phosphorus (P) and potassium (K), carbon (C) respiration, N mineralization, soil enzyme activity, microbial biomass and mycorrhizal infectivity potential were measured to assess soil fertility and biology. The hay mulch treatment increased nutrient availability and soil biological responses, and produced high spinach yields. The straw mulched treatment had a delayed effect on N availability and lower spinach yields initially, but in subsequent years both yield and biological parameters increased in the straw mulched treatments. Both mulch treatments produced cumulative spinach yields comparable to or exceeding the N-fertilizer plots. Only slight differences in total phenolic concentration and antioxidant capacity were measured among treatments indicating that other factors likely influence spinach phytochemicals more strongly than SOM. Measuring biological responses can be a sensitive measure of soil function and an important addition to farm management to better estimate how different management practices will affect soil processes, yields and the environment.