Interseeding: Overcoming the Challenge of Establishing Cover Crops

Climate change, erosion, degradation of topsoil: all pertinent issues facing farmers today. Agricultural innovations seek to prevent further damage to arable land, as well as mitigate the risks of climate change and increase efficiencies in production. Interseeding is the latest in a long list of options available to farmers who are keen to invest in new methodologies for their crops.

Cover cropping

According to the 2015-2016 Cover Crop Survey, in the last five years, cover crop acreage per farm in the USA has more than doubled. Farmers are increasingly investing in methods and technologies which not only increase their yields, but improve the health of their soils. Cover cropping protects and nurtures existing crops and soil by conserving moisture and preventing erosion between harvesting and planting. Furthermore, breakdown of cover crops into plant-ready nutrients boosts the nutrient density and biodiversity of soils; directly benefiting future seasons’ crops.

“Sufficient WCC (winter cover crop) biomass is essential to achieving soil health benefits such as nitrogen cycling, reduced soil erosion, offsetting carbon losses via grain harvest or biomass removal, and pest control.” Cornell Sustainable Cropping Systems Lab

While cover cropping presents huge potential benefits to farmers and to the Earth at large, the method is not without its issues. Problems posed by cover cropping include short windows of opportunity for farmers to plant cover crops once their harvest is complete. This especially affects farms in regions of harsh winters, where even ‘winter crops’ struggle to resist the extreme temperatures. After cash crops are harvested, establishing cover crops in time to prevent soil degradation is integral to maintaining soil quality.

The time and effort involved in seeding and establishing a cover crop is another real hurdle faced by farmers. The labour costs alone add a significant burden to already stretched budgets, not to mention the cost of purchasing seed and establishing the crop.

“The biggest problem for farmers wanting to utilise cover crops is getting started. According to the Cover Crop Survey, cover crop establishment was the No. 1 ‘major’ challenge reported among cover crop users, at 32%. Time and labour required for seeding and managing the cover crop came in third at 31%. Also, in some areas of the U.S., particularly in northern states, there may not be enough time to get cover crops seeded after harvest to achieve decent cover crop growth before winter.”

The challenges faced by Australian farmers are much the same, although climate and seasonal differences play a role.

Interseeding

Interseeding involves sowing cover crops into existing cash crops before they are harvested. This allows the cover crop to become established before the cash crop is removed, and erosion and dehydration can start to occur. The difficulty with interseeding lies in the timing. It is imperative to minimise the competition between each crop, and ensure that the original crop does not suffer as a result. Furthermore, the cover crop must be given enough time to establish itself, in order to withstand the harvest and be prepared for the upcoming seasonal change.

Unsurprisingly, this delicate balance of timing is a difficult thing for farmers to perfect. More often than not, a number of trial-and-error seasons are required before the method is of any substantial benefit. Choosing cover crops which are hardy, and yet do not compete with the cash crop can also be difficult. According to Vern Grubinger of the University of Vermont, crops such as vegetables can suffer from competition with cover crops, and are also at greater risk of disease outbreak.

“A more serious concern with these systems is the possibility of disease enhancement, since crop residues are not ploughed under at the end of the growing season. Hence, interseedings are not advisable if there are serious disease problems in the crop.”

Grubinger suggests that in cases where disease is an issue, it is not advisable to interseed. Tilling and the use of pesticides may be necessary to avoid further breakout and disease carry-over into oncoming seasons. Furthermore, in dry seasons, and where irrigation is not an option, interseeding can cause serious issues of competition for the cash crop.

Planting the most suitable crop for interseeding is not an exact science, however there are a few established principles which will give farmers the best chance of success. Planting deep-rooted crops alongside shallow-rooted versions can reduce competition for nutrients and moisture, while also accessing nutrients which would normally be out of reach for the cash crop. This strategy increases the nutrient density of the topsoil, once the cover crop is levelled. Australia’s Cover Crop Finder guide can assist in choosing a suitable cover crop based on temperature and annual rainfall, as well as cash crop variety. For farmers trying out interseeding or cover cropping for the first time, this guide can alleviate some of the painful trial-and-error involved and provide benefits from the very first endeavour.

Jason Webster of Beck’s Hybrids Practical Farm Research shows us a little about their interseeding trial back in 2015.