Zone Sampling for Soil in Alfalfa Production

Soil Types

• Soil varies in texture, composition and porosity. Sandy soils are highly porous, have a gritty texture and are composed of large particles. Clay soils are dense, have a smooth texture and are composed of small particles. Within these two extremes are a variety of loams. Sandy loams have a high amount of organic matter, making them slightly less porous than sandy soil. They also have smaller particles and a rough texture. Clay loams are also high in organic matter, making them less dense. Their particles are larger than those of clay soils. Alfalfa grows best in sandy loams. The crop requires loose soil and good drainage.

Zone Samples

• All soil types can be present within a single field. To determine which crops will grow best in which area, farmers and soil scientists take and test soil samples. The grid sampling method requires soil testers to systematically test portions of the growing area within a range an established reference point. Zone sampling does not require as many soil samples. Instead, growers take samples from areas with different crop histories and yield histories as well as from areas with varying topography. Once zones have been established, the grower will find that they have fewer growing zones than they would have had they used the grid zone method. This might prove beneficial in terms of fertilization requirements and crop planning.

Fertilization and Maintenence

• The less variation in soil conditions, the fewer zones for a farmer to manage. Growers can also plant crops in areas where they are likely to thrive. Alfalfa, for instance, is best grown in well-draining zones. Knowing the fertilization needs of a specific area means that fertilizer use is specific to that region.

Considerations

• Zone sampling should be conducted yearly, especially on sandy soils where nutrients are readily lost. Growers can choose the zone they wish to sample based on the crop's success or failure. They can also plan to rotate alfalfa with other cover crops that would do well in the zone, or benefit from the nitrogen that alfalfa often leaves behind.