The practice of nurse cropping is an agricultural technique where a temporary crop is planted to support the establishment of a main, often more sensitive, cash crop. This method is an example of inter-cropping, assisting in the successful growth of the primary plant by offering a supportive environment during its fragile seedling phase. It leverages the rapid growth of one species to benefit the slower development of another, creating immediate, favorable conditions in the field.
Defining Nurse Crops
A nurse crop is an annual, fast-growing species sown concurrently with, or just before, a slower-growing perennial or main crop. Its primary role is to provide temporary protection and support to the young seedlings until they are robust enough to thrive on their own. The term applies most widely in the establishment of perennial forage crops, such as alfalfa, clover, and perennial grasses.
The temporary nature of a nurse crop distinguishes it from a standard cover crop, which is typically grown for longer periods to improve soil health, organic matter, and nutrient cycling. While a cover crop’s benefits are long-term and focused on the soil ecosystem, a nurse crop’s function is immediate and directed at the physical protection of the cash crop seedlings. The nurse crop is eventually removed or dies back once the main crop is established.
Primary Functions in Field Management
One benefit of using a nurse crop is its ability to provide effective erosion control and soil stabilization. The rapid establishment of its root system and above-ground biomass quickly creates a physical barrier that intercepts rainfall, reducing the impact energy on the soil surface and slowing runoff. This immediate canopy cover stabilizes the topsoil, which is important in fields newly seeded with slow-to-establish perennials.
Nurse crops are also effective at weed suppression by out-competing undesirable plants for light, water, and nutrients. Their aggressive, early growth shades the soil surface, preventing weed seeds from germinating and reducing the vigor of emerging weeds. This competitive shading is a form of natural weed management that can reduce the need for herbicide application during the main crop’s establishment year.
These temporary crops modify the microclimate surrounding the tender seedlings of the main crop. Taller nurse crops act as a windbreak, reducing wind speed across the soil surface and minimizing the risk of desiccation and wind erosion. They also provide shade, protecting broadleaf seedlings from intense sunlight and high temperatures. This shelter is beneficial for species susceptible to sunscald or frost damage.
Selecting Appropriate Nurse Crop Species
The selection of a nurse crop species is governed by its ability to establish quickly without becoming overly competitive with the main crop. Ideal species exhibit rapid germination and early growth but do not develop dense, aggressive root systems that would starve the primary crop of resources. The species must also be easy to terminate or naturally die back at the appropriate time in the growing season.
Oats are a common choice in agriculture due to their wide adaptability, low seed cost, and ease of management. Other small grains like spring barley, spring triticale, and cereal rye are also frequently used, often providing a harvestable grain or forage yield alongside their protective function. Annual ryegrass is sometimes used for its fast establishment, but it can become aggressively competitive if not properly managed. The choice often depends on the season, with cool-season annuals like oats used for spring plantings and warm-season grasses like teff grass or millet for summer perennial establishment.
Termination and Subsequent Crop Establishment
Once the main crop has developed sufficient root structure and leaf canopy to withstand environmental pressures, the nurse crop must be terminated to prevent competition for resources. The timing of termination is a delicate balance, aiming to maximize protective benefits while ensuring the nurse crop does not inhibit the long-term growth of the cash crop. If left too long, the nurse crop can shade out the seedlings, reducing their vigor and stand density.
Termination is often achieved through mechanical methods, such as mowing or clipping the nurse crop at a height that does not damage the underlying seedlings. Mowing also stimulates perennial grasses to tiller, helping to thicken the final stand. Alternatively, the nurse crop may be harvested for hay or grain, effectively removing the biomass. Targeted chemical termination with herbicides may also be necessary, especially if the nurse crop is an aggressive annual species.