Selecting cover crops - not quite “potato, potahto”: One size does not fit all

Updated: Jan 29, 2020

Perhaps a good place to start is at the end. What are you looking to achieve on your farm? And how can you best make use of cover crops in the quest for this ideal?


Written by Kate Volbrecht


Cover crops, or green manures, can be considered a conservation agriculture (CA) tool in improving soil health. Like other CA practices, planting cover crops requires a long-term view – taking small steps in this building process.


“A cover crop can meet any number of objectives, or combination thereof. Identifying this aim is vital in achieving success.”

Objectives can range from farm to farm – based on variables such as cash crop type and rotation; climatic and weather conditions; location; soil type; and disease or pest pressures.

In potato production, certain objectives and challenges are often experienced. The most common of these are:

Increasing soil health:

Commercial potato production often requires intensive management practices that may have a negative impact on soil health – soil structure, organic matter levels, erosion risk, and nutrient cycling. These practices often include frequent tillage, on-field traffic, or soil fumigation.


Incorporating cover crops into the rotation will assist in alleviating the effects of these management practices. Preceding potato planting, soil tilth and nutrient uptake can be improved – leading to an increased yield and crop quality. Cover crops following potatoes can act as a “catch crop” – preventing nutrient leaching and protecting the soil against erosion and compaction.


Plant selection, timing, and crop duration will determine the volume of organic matter produced. Crop management practices (such as your method of termination) will affect the speed of residue decomposition and its ability to protect the soil as a “mulch”.


Suppression of nematodes:

As nematodes can only move a short distance, and cannot “migrate” between fields, it is vital to tackle nematodes in-field head on.


Fallow soil can reduce nematode numbers. However bare soils come with their own set of challenges -such as soil erosion, moisture evaporation and more dramatic variances in soil temperature. Should weeds grow during this time, certain species can act as hosts to nematodes – continuing the increase of their numbers.


Cover crops can be used to combat certain plant-parasitic nematodes; however the correct plant selection is vital. Results will depend on the effective selection of both plant type and cultivar, in relation to the specific nematode species present.


Single species cover crops can be selected to break the build-up of nematode numbers. Consider all objectives to be achieved prior to selecting the crop type. Examples include:

  • Sunhemp (Crotalaria juncea) is a summer legume option that produces high levels of biomass and organic Nitrogen, suppresses weeds, and curbs erosion.

  • Sorghum-Sudan grass hybrids, also grown in the warm-season, are a high-bulk grazing option.

  • Although nematode activity tends to decrease through the colder months, cereals such as Oats (Avena sativa) can produce residue that will last into the warmer months. Temperate cereals offer a dense cover to protect the soil, build organic material, offer grazing at times of feed shortage, and can be bailed.

  • Plants such as Marigolds (Tagetes spp) produce allelochemicals found to be effective in suppressing many nematode species.

Multi-species cover crops should also be considered in rotations – to encourage biodiversity. Each plant brings with it its own set of characteristics or advantages, which encourage an “ecosystem” below the soil.

Certain cover crop types can act as a “host plant” that provide a habitat and food source for continuous build-up of nematodes. Examples include legumes such as Forage Peas and Vetch. It is important to note that a “host plant” may not show any signs of infestation.


Even when cover crops are used successfully, it is important to remember that nematode numbers can rise again with planting a susceptible crop. Cover crop rotation should be done on a continuous basis to avoid buildup of these populations.


Conclusion:

Most farmers find the use of cover crops to be a learning process - one which requires trial and error. Ensure to document and measure your results, and then adapt accordingly. The insights gained will be unique to your context and particular set of objectives.


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