We are exploring the fate of organic matter mulches in a mixed vegetable cropping system to determine how quantity and quality of SOM affect yields and antioxidant concentrations of the crop. Credited for increasing water-holding capacity and cation exchange, soil organic matter (SOM) is a primary driver for nutrient cycling and a critical energy source for microbial communities. SOM interacts directly with roots, increasing nutrient uptake and influencing root architecture. Despite this broad understanding of SOM function, few studies have directly investigated how SOM quality and quantity influence soil function and aboveground productivity, much less its influence on crop nutritional value. Agricultural systems offer an excellent opportunity to study the relationships between soil chemistry, and plant eco-physiology.
Using a small plot trial in Montana, we measured the decomposition of two mulches, with low and high C:N, over two years and compared spinach yields and antioxidant capacity in the mulched plots to spinach grown in urea-fertilized and untreated control plots. To determine decomposition rates of the different quality mulches, we measured long-term mineralizable nitrogen and carbon, water-extractable organic matter, microbial biomass, %OM and soil C:N ratios from root-zone soil samples. Antioxidant capacity was measured using the Oxygen Radical Absorbance Capacity assay.
Results/Conclusions
We saw significant increases in potentially mineralizable nitrogen (PMN) and carbon (PMC) between the mulched and the non-mulched treatments (p<0.001), as well as increases in microbial biomass (p= 0.014) and %OM (p=0.002) in the mulched treatments compared to the control after one year.
To determine how SOM influenced vegetable yield and antioxidant concentration, we measured spinach response to each treatment. The first year after mulch application, spinach yields were similarly high in the hay, N-fertilizer and control treatments and significantly lower in the straw mulch treatment (p<0.001). Preliminary results indicated that antioxidant capacity was higher in spinach grown in mulch treatments. Tissue samples were analyzed for macro- and micro-nutrient content with no clear pattern emerging in response to the treatments.
By increasing our understanding of the role of organic matter in agroecosystem soil function and its effects on vegetable human nutrition, this research supports the goal of creating sustainable agricultural systems that contribute to the biodiversity of the larger ecosystem while maximizing diverse ecosystem services for humans.