Agriculture and Environment: Sorghum

Environmental Impacts of Production: Soil Erosion & Degradation

Sorghum causes erosion on slopes as shallow as 4 degrees (Buxton et al. 1997), and produces more erosion than most other cultivated crops (Thurman 1996).

The high potential for soil erosion tends to restrict sorghum production to soils with little slope.

When grown for silage, most sorghum foliage is removed from the field when harvested. Soil is then at greater risk for water and wind erosion.

Nitrogen leaching
In addition, nitrogen leaching from the soil can occur from the time sorghum is harvested until the next crop is planted and established. This can be a period of more than 6 months in areas with pronounced dry seasons or winters.

When grown as a grain, these issues are present but not as pronounced. Sorghum produces considerable foliage, which, if left in the field, acts as an effective mulch, especially if chopped at harvest.

No-till practices for better soil health
No-till practices can also reduce the impact of sorghum production on soil erosion while increasing soil health. Meyer et al. (1999) found that on research erosion plots, no-till practices reduced soil erosion for sorghum by more than 80%.

Exploiting land, adopting inappropriate production practices
As a result of population pressures in most African countries, fallow periods are being shortened and more marginal lands are being brought into cultivation. These marginal lands are farmed with little or no fertiliser, and the cultivation methods used (e.g., planting rows without regard to incline) can be a major cause of soil degradation.

In addition, changes in climate such as lower rainfall levels and higher temperatures lead to periodic drought, which makes cultivation riskier. These factors force farmers in parts of Africa to adopt inappropriate production practices. The net result is production practices that are unsustainable in the long term coupled with declining productivity in the short term (FAO and ICRISAT 1996).

Grain sorghum - a soil-depleting crop
Farmers have long observed that sorghum is "hard" on the soil. Grain sorghum is a soil-depleting crop because its fibrous root system is deep (relative to other crops such as corn or millet) and extensive; it fills the rhizosphere and uses up the nutrients present in the soil (Ross and Webster 1970). Still, these are precisely the characteristics that make the plant drought-resistant and able to tolerate marginal soil.