Project Overview

View the project final report

• 2015 annual report

Commodities

• Agronomic: corn, rye

Practices

• Crop Production: application rate management, cover crops, crop rotation, nutrient cycling, tissue analysis

• Production Systems: general crop production

• Soil Management: green manures, nutrient mineralization, organic matter, soil analysis, soil microbiology, soil quality/health

Introduction:

Corn (Zea mays) and soybean (Glycine max) rotations are the major land use in Iowa.  While these systems are highly productive, conventionally managed corn-soy systems usually require large applications of nitrogen fertilizer during the corn year to achieve high corn yields.  Most corn-soy systems lack a growing crop in late winter and early spring, which elevates the risk of nutrient losses to the environment, which in turn impacts farmer profitability and environmental quality.  Adding an overwintering small grain mixed with a frost-seeded legume to the corn-soy rotation may reduce mineral N fertilizer requirements and mitigate negative environmental impacts of this cropping system.  The small grain provides cover in the late fall to early spring period to reduce N losses, and the legume acts as an N source to the following corn crop.  Cereal rye (Secale cereale) has gained popularity in Iowa as a winter cover crop following soybean in corn-soybean rotations due to its ability to overwinter successfully.  Consequently, the increased demand for cereal rye seed has increased the price of rye grain, which may favor the economics of growing cereal rye for grain.  Cultivation of cereal rye for grain offers the possibility of frost-seeding a legume into the standing rye crop in early spring, where the legume can produce biomass and fix N following rye harvest.  Red clover (Trifolium pratense) is well adapted to frost-seeding into a small grain and can produce a large amount of biomass with significant N content following small grain harvest.   The clover biomass will decompose following termination, gradually releasing N during corn growth which could potentially replace part of the fertilizer required for corn. 

While crops have traditionally been thought to utilize only mineral N that soil microbes fail to immobilize (i.e.net mineralization and nitrification), recent findings suggest that they can also successfully compete with microbes for actively cycling mineral N (i.e. gross mineralization and nitrification).  This suggests that N availability is controlled by both the pool size of mineral N in the soil as well as the gross rates of N cycling.  Diversified cropping systems that utilize legumes as a major N source could maintain high rates of gross N cycling, producing a stream of mineral N from a large organic N pool which is rapidly taken up by plants or microbes.  We proposed that including cereal rye/red clover in corn and soybean rotations will enhance both net N mineralization and gross N mineralization, and thus increase N supply to a subsequent corn crop.

This project quantified N uptake, net N mineralization, and gross N mineralization in a corn crop following cereal rye/red clover.  Utilizing two established on-farm trials in eastern Iowa, we measured soil and plant N in the corn year of corn-soy-rye/clover rotations.  Results of this project were shared with farmers and researchers to improve awareness of the feasibility of utilizing small grain/legume mixes to diversify corn-soybean cropping systems and attendant effects on N cycling.  This information will contribute to the development and implementation of cropping systems that will enable farmers to better optimize N fertilizer application rates in diversified cropping systems, providing high levels of productivity with reduced input costs while simultaneously improving environmental quality in Iowa.