Effects of Organic Amendments on Soil Humic Substances Content and Physiological Properties of Water-Stressed Zea mays and Glycine max
Water stress is the most critical environmental factor limiting crop production in the southeastern United States Piedmont due to high evapotranspiration rates and low plant available water. Plants have evolved an antioxidant defense system to ameliorate this oxidative stress. Organic waste production has increased dramatically over the last three decades due to improvements in solids removal from wastewater treatment plants, and increasing animal units in confined animal farming operations. Land application of organic amendments may improve soil quality and enhance plant metabolic processes via the presence of humic-like substances found in these materials.
Since 1999, commercial inorganic fertilizer and several organic amendments have been applied to a Fauquier silty clay loam (fine, mixed, mesic Ultic Hapludalf) at the Northern Piedmont Agricultural Research and Education Center (NPAREC) in Orange, Virginia. Inorganic fertilizer, poultry litter, biosolids compost, and poultry litter-yard waste compost were applied at rates designed to supply 100% of crop requirements. Biosolids and poultry litter-yard waste composts were also applied at rates to supply 30% of crop needs. We hypothesized that soil chemical and physical properties, leaf metabolic processes, and seed yield and quality would be improved under organically amended fertilization regimes as compared to inorganic fertilizer.
The objectives of this study were to compare the effects of inorganic fertilizer, poultry litter, biosolids compost, poultry litter-yard waste compost on soil fertility, organic matter, humic and fulvic acid contents; leaf chlorophyll content, photochemical efficiency, antioxidant activity; and seed yield, starch, oil, and protein contents of Zea mays.
The summer 2004 growing season was unusually wet. Differences in yield and leaf health were primarily due to nitrogen availability and not nitrogen source. Treatments that provided 100% of the crop’s N requirement had the greatest chlorophyll contents and photochemical efficiencies.
There was a strong association between photochemical efficiency and leaf antioxidant activities as noted by increased superoxide dismutase and ascorbate peroxidase activities in the less photochemically efficient (30% N and 0% N) treatments.
Yields in the 100% N treatments were 95-115% greater than the non-fertilized control, and yields in the 30% N treatments were 45-63% greater than non-fertilized control.
Seed protein (8%) and seed oil (4%) contents were greatest in the agronomic nitrogen treatments. Seed starch (62%) was greatest in the control and low nitrogen treatments. These seeds were also less mature during harvesting as noted by increased seed moisture (29%). We concluded that nutritional stress during the reproductive period resulted in less photosynthate translocation and extended the grain fill period causing less mature seeds in these treatments.
Soil fertility (as measured by extractable soil nutrients) and organic matter concentrations were greatest in the treatments that received the 100% of the crop N requirements. Further analyses are being conducted to determine treatment effects on soil humic substances content.
Impacts and Contributions/Outcomes
These data have been presented at the American Society of Agronomy International meetings (November 2004) and before the External Review Team of the NPAREC. We will also present our results at the NPAREC Annual Fall Field Day (September 2005),and at the biennial “Composting in the Mid-Atlantic Conference” (September 2005). We anticipate publication of three refereed journal articles based on this study, and the development of an extension publication, “Managing Composts for Agronomic Crops.”
417 Smyth Hall
Crop andf Soil Environmental Sciences
Blacksburg, VA 24061-0404
Office Phone: 5402319803