Agriculture and Environment: Sorghum

Better Management Practices: Build the Soil

The use of cover crops and crop rotation help build and maintain the soil.

The introduction of organic matter and green manure build and maintain productivity. In addition, these same treatments reduce the already-low fertiliser and water needs of sorghum as the organic matter binds more effectively with the nutrients and water available naturally.

Detrimental to soil health
Sorghum production reduces soil vitality through the direct exposure of soil to sunlight during preparation for planting and the period of time it takes the crop to form a canopy over the soil.

No-till sorghum or interplanting sorghum with cover crops has been found to decrease runoff more than other cultivation methods (Meyer et al. 1999). This approach can reduce soil erosion by more than 80% and decrease runoff by at least 10%.

Soil erosion from wind and water is one of the most obvious impacts of sorghum production. In many parts of the world the better management practices are basic.

Plant horizontally, running rows
Producers should not plant up and down the hillsides. Rather, they should plant horizontally, running rows perpendicular to the slope. Similarly, if wind tends to come from one direction, then rows should be planted perpendicular to the direction of the wind so that the tall rows act as miniature windbreaks.

Continuous farming
Another BMP to reduce soil degradation is continuous farming. This refers to crops that are grown in sequence within a year, in contrast to crop rotation that occurs over a number of years.

Farmers in many parts of the world are finding that planting an off-season ground cover (especially a legume), even if it does not provide a marketable crop, improves subsequent yields of other crops. The more biomass produced by the ground cover, the higher the subsequent yields.

Using residue as mulch
Soil erosion can also be reduced by chopping and leaving large amounts of crop residue from grain sorghum on the field after the harvest. If the residue is mulched, this is an even more effective way to control soil erosion (McCarthy et al. 1993). Sorghum crop residue benefits the soil by assisting moisture retention. This, in turn, maintains beneficial organisms near the surface of the soil that assist with the recycling of nutrients into forms that are available to plants.

Benefits of sequence planting
In the United States, a continuous cropping system of winter wheat-fallow-grain sorghum-fallow has been shown to conserve soil and water resources (Getachew et al. 1997). Annual plants such as sorghum, corn, and millet can make effective vegetation barriers if they are in place during critical erosion periods (James and Croissant 1994). Planting a sorghum crop in the summer-autumn period can also help to prevent soil erosion.

An additional benefit of this sequence planting is that sorghum provides food for wildlife during a period of scarcity. On the Great Plains in the United States, producers often plant sorghum to attract wildlife, which then also attracts either eco tourists or hunters (Rollins et al. 1997).

Using this system, ranchers can generate up to 25-50% of their total income from the sale of hunting permits (Greg Simmods, personal communication). Since this has gone on for many years, it appears that the hunting off-take levels must be reasonably sustainable.