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Nitrogen in - weeds out

High and stable yields can be achieved in organic crop farming by growing legume-based catch crops in the row space between agricultural crop rows. The method can reduce weeds and supply nitrogen for agricultural crops and may also reduce nitrogen leaching and increase carbon storage in soil.

2014.02.01 | Janne Hansen

Planting with wider row spacing than normal provides room for catch crops which in turn has several benefits. Scientists are investigating the new row cropping system. Photo: Janne Hansen

Organic growers face several significant challenges if they are to achieve high and stable crop yields. One of the challenges is to control aggressive weeds; another is to ensure an adequate supply of nitrogen for the crops. 

Scientists from Aarhus University are now starting a new project that can both generate higher and more consistent yields for organic farmers and reduce the impact on environment and climate. The method consists of growing catch crops in the rows between the main crop rows and in this way allowing effective mechanical weed control. 

In the project, the scientists will develop and test the row cropping system, taking advantage of the latest knowledge and developments in sensor and GPS-guided row cropping equipment. Once the system has been developed and evaluated, it will be demonstrated on-farm so that knowledge of the system can be shared and used in organic farming. 

- Wider row spacings of cereal crops will provide enough space for mechanical hoeing between the rows and for sowing nitrogen-fixing catch crops that can capture nitrogen for subsequent crops, explains the project leader, professor Jørgen E. Olesen from Aarhus University. 

Catch crops between rows

Some of the weeds that organic farmers are attempting to control are extremely stubborn and reappear year after year. One example is the perennial creeping thistle. Normally, perennial weeds are controlled by harrowing in the autumn making it difficult to established effective catch crops, thus increasing the risk of nitrate leaching into the aquatic environment. 

With the new row-cropping method, agricultural crops are grown with a wider space between rows than normal. This permits both hoeing and the establishment of catch crops between the rows. Following the harvest of the main crop, the weeds between the rows of the catch crop can be hoed. With a greater distance between rows, the catch crop will get more direct sunlight, boosting their growth and thus also increasing their biological nitrogen fixation. In the autumn the troublesome weeds between the rows of the catch crop can be controlled. 

New technology has made it easier and more effective to practice this kind of row cropping and weed control, but there is a dearth of knowledge about its effect on yield, weeds, carbon storage and nitrogen leaching. These are some of the aspects that the new project will be looking into. 

Economic and environmental gains

The new cropping practice has good economic and environmental prospects. The scientists expect that the new system will be able to increase crop yields by 1.2 t/ha, corresponding to 100 million DKK nationally. The reduction in nitrogen leaching is expected to be 10 kg N/ha, which is 500 tonnes of nitrogen for Denmark as a whole, while the climate will be spared emissions of 200 kg C/ha, equivalent to 37,000 tons of CO2 nationally, due to increased carbon storage in the soil. 

- Since the new system can provide more nitrogen for the organic crops, it could persuade farmers to phase out the import of manure from conventional farming and could lead to more farmers choosing to establish or to convert to organic farming, says professor Jørgen E. Olesen. 

The project, RowCrop, has been awarded 12.5 million DKK by the Green Development and Demonstration Programme under the Ministry of Food, Agriculture and Fisheries. Project participants are, besides Aarhus University as project manager: University of Copenhagen, Knowledge Centre for Agriculture, agricultural consultants Gefion, Barritskov estate and Kongskilde Industries A/S.

The project is an Organic RDD2 project, which is funded by the Ministry of Food, Agriculture and Fisheries and coordinated by the International Centre for Research in Organic Food Systems (ICROFS).

Further information: Professor Jørgen E. Olesen, Department of Agroecology, e -mail: jorgene.olesen@agrsci.dk, telephone: +45 8715 7778, Mobile: +45 4082 1659




DCA, Technology, Agro, Forædling og plantebeskyttelse