Organic Cover Crops

Cover crops are a part of any certified organic plan, and their importance is growing in all agriculture systems for many reasons.  Unfortunately, they can also be a source of frustration (for many reasons!) and this year some of the top reasons are the short supply of seed, high prices, and the persistent drought.  Still the benefits can certainly outweigh the costs and include:

Cover crops improve soil health.  The living soil microbiome must have plant roots to survive, and plants need that soil microbiome to produce.  Growing cover crops provides roots and consequently root exudates. Microbes feed on the exudates and then the roots feed on what the microbes leave behind, namely plant nutrients. Also, there are lots of fauna (insects and animals) that live and feed in and on those cover crops.  This includes earthworms, potworms, beneficial nematodes, collembola (springtails), etc.  These insects and animals play a huge role in breaking down organic matter, removing weed seeds and creating soil aggregates.

Cover crops reduce water use.  We commonly talk about EvapoTranspiration rates in agriculture.  This summer it is not unusual to see ET rates over 0.4 inches per day.  ET is drastically reduced with soil cover and becomes T (plant transpiration) with soil cover.  Added to reduced water use is the ability of soils with cover crop residue for taking in and holding or storing more water!

Cover crops lower soil temperature.  This is often overlooked but with air temperatures over 100° we can see soil temperatures rise to over 120°.  This will affect root development negatively in the top few inches of soil, and this is where we irrigate roots.

Cover crops are fertilizer. They are a significant source of nutrients with nitrogen being the primary. Everyone knows that legume cover crops are a source of nitrogen, but all cover crops are a source of nitrogen!  But they are also a source of most major and minor nutrients too.  It is not unusual for a good crop of cowpeas to supply 100 units of N to the following crop plus P and K.  Also, the microbiome around cover crop roots is taking in many micronutrients and chelating them for future use by crops.

Cover crops help control pests. There is a lot of research that shows how cover crops “recruit” beneficial insects, fungi and bacteria preventing plant pathogens.  They basically start the beneficial cycle so that when you plant your cash crop, they are in the soil or in the above ground cover ready for “prey” (aphides, mites, caterpillars, etc.) to eat.  For instance, cowpeas have floral nectaries in the petioles and leaflets that attract beneficial insects to the plant.