Does Adding a Cover Crop Make Sense in a Semi-arid Climate?

Kristi Bartolo, Pueblo County Agronomy Agent

Cover cropping is one of many strategies that are incorporated in soil health principles. These crops have the potential to improve soil quality and health, ultimately improving cash crops as well. Cover crops fore mostly provide “cover”, act as a blanket on bare soil while a cash crop is not present. This cover reduces soil erosion from wind by holding onto the soil and reducing wind speed at the soil surface. Water erosion is also decreased as less run off occurs by leaves and litter capturing and delivering the water to the deeper soil profile. Cover crops provide living roots for soil microbes to build relationships with, create improved soil aggregates, and improve soil pore space. These crops increase diversity in a field rotation and, if nothing else, can be a livestock forage solution. The actual plants of cover crops often include species of grasses (annual ryegrass, oats), legumes (peas, clovers), and brassicas (radish, canola).

Though these crops have a myriad of attributes, growing them does take effort and resources. Pueblo County [and most of southeastern CO] can be classified as semi-arid to arid, receiving only 13 inches of precipitation annually. This makes water the most limiting factor for growing cover crops or any extra crops in one season. This portion of the Arkansas Valley relies heavily on surface and underground water for irrigation, without which crops would not grow. The irrigation water comes from snowmelt in the Rocky Mountains and so, low snow-pack years can cause major cropping issues and ground is often left fallow, bare, and exposed.

The question then stands; is it feasible to grow a cover crop in a place with little moisture? This question can be answered by gaining a better understanding of soil moisture. Soil moisture is the water in the soil profile, especially that which is available for plants to take up. The amount of moisture soil can hold depends on the number of pore spaces within the soil profile. More pore space means more places for water to be. When there is a surplus of soil moisture (in the profile or from precipitation) and irrigation water, growing extra crops makes sense, helping to improve soil and potentially reduce feed costs. When soil moisture is low or inadequate, the cover crop might sap any reserves leaving the cash crop to struggle when it comes time to plant and so it would seem less desirable to plant a cover crop.

This growing season has been exceptionally wet so far with just over 7 inches of precipitation. Years like this do not come along too often and should be taken advantage of. This is the time that a cover crop could be planted successfully without causing undue stress on the soil moisture profile and not requiring much supplemental irrigation water to be taken from the cash crop. All the while, the benefits from having the cover crop can slowly increase the soil’s ability to hold on to even more moisture when it comes along.

Though observation of the good effects of a cover crop may not be seen for many years, the gradual improvement of the soil profile can help to ensure successful cash crops for many future generations.