Improving Soil Quality During and After Organic Transition

Improving Soil Quality During and After Organic Transition

Summary

Organic agriculture continues to expand in the U.S. but strategies to optimize biological turnover to enhance soil quality in transitional organic farming are not well understood. A long-term organic research site has been established to examine the short- and long-term physical, biological, and economic outcomes of certified organic and conventional cropping systems. The ISU Neely-Kinyon Long-Term Agroecological Research (LTAR) farm is a systems experiment where treatments consist of a suite of farmer-developed practices (soil amendments, tillage, crop selection/rotation) established as complete management strategies. In addition, three on-farm sites were selected to monitor changes during the transition and beyond certification.

Objectives/Performance Targets

In this research, we are testing the hypothesis that organic systems relying on locally derived soil fertility inputs are capable of providing stable yields, while maintaining soil quality and plant protection, compared to conventional systems with less diverse crop rotations and greater levels of external, fossil-fuel based inputs. This project was started in 2006 to building on farmer-based experiences and our long-term research program experience to address the following research objectives:

Objective 1: Examine the effects of required organic farming practices, including crop rotations, cover cropping, compost application, and non-chemical weed control, on soil quality, crop yield and grain quality.

Objective 2: Examine how soil organic matter (SOM) quantity and quality influence the interrelationships among soil fertility, crop resistance to pests and diseases, and environmental conservation of nutrients and carbon.

Objective 3: Determine which crop rotations and nutrient management practices will increase the crop’s competitiveness with weeds, build soil fertility, and maximize biological control of insect pests and diseases.

Accomplishments/Milestones

In the first year of the sampling, distinct differences were noted in soil quality, with longer years in organic production leading to higher soil quality. Accomplishments and milestones included establishing a collaborative environment with farmer-cooperators with significant participation from farmers. Two of the farmer participants, Ron Rosmann and Earl Hafner, presented information on project results and concepts of soil quality in organic farming at the Iowa Organic Conference on November 19, 2007, at Iowa State University, Ames, Iowa. a total of 92 farmers and ag professionals participated in these sessions.

Impacts and Contributions/Outcomes

LTAR 2007 Summary

Five randomly-located soil cores (0-15 cm) were removed from each plot in the fall after harvest but before plowing. The cores were mixed together to produce one composite sample from each plot. Soil quality was higher in the organic rotations relative to the conventionally managed corn-soybean rotation. The organic soils had more soil organic carbon, total N, biologically active organic C and N, higher P, K, Mg and Ca concentrations and lower soil acidity than conventional soils. Macroaggregation was especially high in the soybean-winter wheat system, possibly as a result of the dense rooting system of winter wheat and relatively fewer passes with the moldboard plow. The 3-yr organic rotation had higher inorganic P and K concentrations than the 4-yr organic rotation reflecting the greater manure application intensity (2 of 3 yrs) in the 3-yr rotation. Soil quality enhancement was particularly evident for labile soil N pools, which are critical for maintenance of N fertility in organic systems, and for basic cation concentrations, which control nutrient availability through the relationship with CEC.

2007 Organic Farm Summary

Soil samples (0-15 cm) were removed from 3 fields at each of the organic farms. Crop rotations at all the farms included corn, soybean, small grains and forage legumes. Soil biological, chemical and physical properties for the Errett Farm (Table 1) indicated overall soil quality was highest for Field 8 compared with Field 7 and 9. This result is similar to data collected in May 2006. Soil organic C, total N, particulate organic matter C and N, microbial biomass C, N mineralization potential, and macroaggregation were all significantly higher for Field 8. Soil quality at this field may be greater because alfalfa hay was cropped in this field during 2003 and 2004. We also observed higher values for some of the soil properties related to soil quality for Field 3 compared to Field 2 and 4 at the Hafner Farm (Table 2) but this pattern was not as consistent as what we observed in 2006. Soil organic C, total N, and N mineralization potential were significantly greater for Field 3 but particulate organic matter C and N, and microbial biomass C were not. Field 2 was planted to barley/clover in 2006 and field 4 was cropped to corn, which received manure. The forage legume and manure impacts on soil quality may account for the 2007 differences among the 3 fields relative to 2006 data. Patterns in soil properties related to soil quality at the Rosmann Farm were less definitive than the other 2 farms (Table 3). Nearly all of the soil properties we measured trended lower in Field 9, relative to Field 6 and 16, but the difference was significant only for soil organic C. No consistent pattern emerged for differences among the fields at the Rosmann Farm.

One of the most significant outcomes to date is the result that the organic soils had more soil organic carbon, total N, biologically active organic C and N, higher P, K, Mg and Ca concentrations and lower soil acidity than conventional soils. With organic farming often criticized for excessive tillage, and the potential for degradation of soil carbon pools, this research shows the opposite: organic farming can lead to increases in soil quality, including carbon pools. Farmers participating in this research also show more interest in lowering tillage operations and improving soil quality. In the next year of the project, we will seek to quantify these changes in behavior and knowledge, in addition to soil quality changes on participating organic farms.

Collaborators: