Conditions for growing small grains

The rainfall, humidity, temperature and soil conditions need to be perfect for the growing of small grains. A farmer must also look at the soil’s condition and tillage options for a better yield.

Rainfall and humidity

Sorghum wants 400-800 mm rainfall per year. The high humidity during seed ripening and maturation promotes diseases like grain mold.

Pearl millet wants 200 – 600 mm rainfall per year and finger millet 500-1000 mm per year.

Soil conditions

Small grains are adapted to a wide range of soil conditions ranging from clay, clay loam up to sandy loam soils. They all tolerate salinity better than most grains but perform best when grown on well drained, fertile soils.

Sorghum

Sorghum wants well drained, fertile, sandy, clay loam soils and a pH range from 4,5 to 7,5. Sorghum will not grow in soils heavily infested with witch weed (Striga).

Pearl millet wants fertile, well drained loamy soils with a pH range of 4,0 to 7,5. It is tolerant of shallow soils and dry conditions, and it does not grow well on water logged soils.

Finger millet wants fertile and well drained soil with a pH range of 5,0 to 8,2.

Agronomic practices

Cultivar selection

A number of improved sorghum, pearl millet and finger millet varieties have been developed and are available in Zimbabwe. Appendices 1, 2 and 3  show the characteristics of various available varieties for sorghum, pearl millet and finger millet respectively.

Farmers can choose varieties best suited to their conditions and needs from the lists. For all three the crops there are some traditional varieties (which are not indicated on the appendices) which have specific characteristics adapted to different areas.

Appendix 1: Sorghum variety

Appendix 2: Pearl Millet variety

Appendix 3: Finger millet

Seed rates

• Sorghum: 7-12 kg/ha
• Pearl millet: 5-10 kg/ha
• Finger millet: 3-5 kg/ha

Crop rotation

Crop rotation is very important for breaking pest and disease cycles as well as for optimal utilisation of soil nutrients. Small grains should be rotated with broad leaved crops such as cowpeas, beans, sunflower, groundnuts or bambara nuts.

Land preparation

Land preparation should begin in advance, well before the onset of the rainy season. The most ideal time to begin land preparation is just after harvesting the preceding crop. The tillage method used will determine how the land will be prepared.

Tillage options

Small grains can be grown under two main tillage options, namely conventional tillage and reduced tillage. Reduced tillage is the more appropriate tillage option for the marginal areas where small grains are mainly grown as it tends to conserve moisture and put the little rainfall received to maximum use.

Reduced tillage

This is a tillage system that involves minimal soil disturbance. There is no ploughing as in conventional tillage, but the soil is only disturbed to create planting stations for the seeds. Under reduced tillage the planting basin method or the ripper-tine method can be used depending on the size of the area to be cropped, availability of draft power as well as the farmer’s preferences.

Conventional tillage

The land is tilled by inverting the soil and burying residues. This may not be a good practice on slopes and where soil erosion is a problem. The current trend is to go the reduced tillage route, given the benefits of the practice.
The three possible tillage methods are highlighted below:

Basin method:

  • Remove weeds from previous season.
  • Dig basins (15 cm long, 15 cm wide & 15 cm deep) at a spacing of 75 cm inter-row and 40 cm in-row
  • The basin guidelines do not apply to finger millet. They are for sorghum and pearl millet.

Ripper tine method

  • Remove weeds from the previous season
  • Open planting on lines on unploughed land using a ripper tine at 75 cm between rows for sorghum and pearl millet and a depth of at least 15 cm
  • For finger millet, the planting rows should be 45 cm apart.

Conventional method

  • Using the conventional plough turns the soil, burying all crop residues and weeds. Ploughing should always be done across the slope
  • If the land has many clods, an ox-drawn harrow can be used to break the clods and create a fine tilth
  • Open planting lines at 75 cm apart for sorghum and pearl millet, and 45 cm apart for finger millet

Small grains have small seeds and so the seed bed or basin must be of fine tilth and free of weeds.

In the next edition we shall discuss fertiliser application. We thank the Zimbabwe government and the Food and Agricultural Organisation of the United Nations for the use of this guide.