Improving Soil Quality During and After Organic Transition

Improving Soil Quality During and After Organic Transition

Summary

Objectives
Building on farmer-based experiences and our long-term research program experience, we intend to address the following research objectives:

Objective 1: Examine the effects of 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.

Results to Date:
Funds for this project were not secured until late in 2005; thus, the initial part of the project entailed coordinating sampling dates with farmer-cooperators for 2006, and collecting crop rotation history from their fields. Soil samples (0-15 cm) were removed from 3 fields at each of the organic farms on May 17-18, 2006. Crop rotations at all the farms included corn, soybean, small grains and forage legumes. Soil analysis was conducted at the USDA-ARS National Soil Tilth Lab, Ames, Iowa. Soil biological, chemical and physical properties for the Errett Farm indicated overall soil quality was highest for Field 8 compared with Field 7 and 9. 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 consistently higher values for soil properties related to soil quality for Field 3 compared to Field 2 and 4 at the Hafner Farm. Soil organic C, total N, particulate organic matter C and N, microbial biomass C, and N mineralization potential were significantly greater for Field 3. All three fields at the Hafner Farm were planted to crop rotations that had 2-3 years of clover in the last 5 years so soil quality differences were likely not due to forage legume impacts. Soil quality at Field 3 may be related to manure applications since this field was planted to corn in 2002 and 2004 whereas Field 2 and 4 were cropped to corn only once since 2002. Patterns in soil properties related to soil quality at the Rosmann Farm were less definitive than the other 2 farms. Soil organic C, total N, and macroaggregation were significantly lower for Field 9 compared with Field 6 and Field 16 but particulate organic matter C and N mineralization potential were equal for all three fields. Particulate organic matter N and microbial biomass C were equivalent at Field 9 and 16 and both were greater than Field 6. Soil biological property differences may be related to alfalfa hay, planted sequentially for 2 years before corn at Field 16 in 2002 and 2003 and at field 9 in 2004 and 2005. Field 6 had only one year of hay at the time of the May 2006 sampling.

The Neely-Kinyon Long-Term Agroecological Research (LTAR) Site Summary
The Neely-Kinyon LTAR site was established in Greenfield, Iowa, in 1998, with a completely randomized experimental design with four replications of four different cropping system treatments. All crops in all rotations are planted each year of the experiment. Cropping system treatments consist of the following crop rotations: conventional corn-soybean (C-S), organic corn-soybean-oat/alfalfa (C-S-O/A), organic corn-soybean-oat/alfalfa-alfalfa (C-S-O/A-A), and organic soybean-wheat (S-W) with a frost-seeding of red clover. Local practices are followed for field preparation, fertilization, seeding rates, weed control and insect pest management. Organic corn plots are amended in early spring (1 month before corn planting) with composted swine manure (a mixture of manure and corn stover) from a deep-bedded swine ‘hoop-house’ structure located at the ISU Armstrong Research and Demonstration Farm in Lewis, Iowa. The manure mixture is composted for a one-year period prior to application in the organic system. Average nutrient content of the compost is 7.8, 9.6, and 13.7 g kg-1 N, P, and K. The compost is applied with a manure spreader to organic corn plots at rates intended to apply 134 kg N ha-1 to match the N rate in the conventional plots. Organic oat plots receive compost at a rate to apply 78 kg N ha-1. Conventionally managed corn is fertilized at planting with 28% urea ammonium nitrate at a rate of 134 kg N ha-1.

Soil sampling at this site has occurred in the fall of each year. Soil cores were taken to a depth of 15 cm in October 2005 and 2006. 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. Soil organic C, total N, N mineralization potential, particulate organic matter C, and microbial biomass C trended higher in the organic systems, although the relative differences varied in 2005 and 2006. 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. Soil fertility was greater in the organic systems that were amended with swine hoop house compost, as evidenced by greater amounts of extractable P, K, Mg, and Ca. Chemical fertilizer application in the conventionally managed rotation resulted in increased soil acidity compared with near-neutral pH values in the organic rotations.

Future Plans
Soil sampling, soil analysis and detailed farm field analysis will be conducted in 2007. Information from this project will be presented at three Practical Farmers of Iowa Field Days; the Agronomy Society of America annual meetings; and at the 2007 Iowa Organic Conference.

Outreach:
As part of the Iowa Organic Conference on November 19, 2006, Earl Hafner and Ron Rosmann, farmer-cooperators, presented information from this project in the “Transitioning to Organic Production” panel. Three-hundred copies of the ISU Extension publication, “Soil Quality for Organic Agriculture” were distributed at this conference.

Objectives/Performance Targets

Objectives
Building on farmer-based experiences and our long-term research program experience, we intend to address the following research objectives:

Objective 1: Examine the effects of 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

Results to Date:
Funds for this project were not secured until late in 2005; thus, the initial part of the project entailed coordinating sampling dates with farmer-cooperators for 2006, and collecting crop rotation history from their fields. Soil samples (0-15 cm) were removed from 3 fields at each of the organic farms on May 17-18, 2006. Crop rotations at all the farms included corn, soybean, small grains and forage legumes. Soil analysis was conducted at the USDA-ARS National Soil Tilth Lab, Ames, Iowa. Soil biological, chemical and physical properties for the Errett Farm indicated overall soil quality was highest for Field 8 compared with Field 7 and 9. 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 consistently higher values for soil properties related to soil quality for Field 3 compared to Field 2 and 4 at the Hafner Farm. Soil organic C, total N, particulate organic matter C and N, microbial biomass C, and N mineralization potential were significantly greater for Field 3. All three fields at the Hafner Farm were planted to crop rotations that had 2-3 years of clover in the last 5 years so soil quality differences were likely not due to forage legume impacts. Soil quality at Field 3 may be related to manure applications since this field was planted to corn in 2002 and 2004 whereas Field 2 and 4 were cropped to corn only once since 2002. Patterns in soil properties related to soil quality at the Rosmann Farm were less definitive than the other 2 farms. Soil organic C, total N, and macroaggregation were significantly lower for Field 9 compared with Field 6 and Field 16 but particulate organic matter C and N mineralization potential were equal for all three fields. Particulate organic matter N and microbial biomass C were equivalent at Field 9 and 16 and both were greater than Field 6. Soil biological property differences may be related to alfalfa hay, planted sequentially for 2 years before corn at Field 16 in 2002 and 2003 and at field 9 in 2004 and 2005. Field 6 had only one year of hay at the time of the May 2006 sampling.

The Neely-Kinyon Long-Term Agroecological Research (LTAR) Site Summary
The Neely-Kinyon LTAR site was established in Greenfield, Iowa, in 1998, with a completely randomized experimental design with four replications of four different cropping system treatments. All crops in all rotations are planted each year of the experiment. Cropping system treatments consist of the following crop rotations: conventional corn-soybean (C-S), organic corn-soybean-oat/alfalfa (C-S-O/A), organic corn-soybean-oat/alfalfa-alfalfa (C-S-O/A-A), and organic soybean-wheat (S-W) with a frost-seeding of red clover. Local practices are followed for field preparation, fertilization, seeding rates, weed control and insect pest management. Organic corn plots are amended in early spring (1 month before corn planting) with composted swine manure (a mixture of manure and corn stover) from a deep-bedded swine ‘hoop-house’ structure located at the ISU Armstrong Research and Demonstration Farm in Lewis, Iowa. The manure mixture is composted for a one-year period prior to application in the organic system. Average nutrient content of the compost is 7.8, 9.6, and 13.7 g kg-1 N, P, and K. The compost is applied with a manure spreader to organic corn plots at rates intended to apply 134 kg N ha-1 to match the N rate in the conventional plots. Organic oat plots receive compost at a rate to apply 78 kg N ha-1. Conventionally managed corn is fertilized at planting with 28% urea ammonium nitrate at a rate of 134 kg N ha-1.

Soil sampling at this site has occurred in the fall of each year. Soil cores were taken to a depth of 15 cm in October 2005 and 2006. 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. Soil organic C, total N, N mineralization potential, particulate organic matter C, and microbial biomass C trended higher in the organic systems, although the relative differences varied in 2005 and 2006. 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. Soil fertility was greater in the organic systems that were amended with swine hoop house compost, as evidenced by greater amounts of extractable P, K, Mg, and Ca. Chemical fertilizer application in the conventionally managed rotation resulted in increased soil acidity compared with near-neutral pH values in the organic rotations

Impacts and Contributions/Outcomes

Outreach:
As part of the Iowa Organic Conference on November 19, 2006, Earl Hafner and Ron Rosmann, farmer-cooperators, presented information from this project in the “Transitioning to Organic Production” panel. Three-hundred copies of the ISU Extension publication, “Soil Quality for Organic Agriculture” were distributed at this conference.

Collaborators: