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R Nyabadza and D Rukuni
Timing of planting is an important factor in tobacco production. Soil texture, which is a measure of the relative proportions of clay, silt and sand in a soil, is an important factor in determining whether a soil should be early- or late-ploughed. Early ploughing is normally done on infertile sands to make best use of the mineralised nitrogen and to conserve moisture.

Late ploughing is mostly done on heavy textured, fertile soils to prevent excessively large and thin leaves by restricting the amount of nitrogen available to the tobacco.

As a rule of thumb, ploughing from January to March/April may be considered as early-ploughed and ploughing from July onwards as late – ploughed. With early-ploughing, the grass is normally disced in January or February and the field ploughed in March or April, that is before the end of the rains when the soil is still moist.

It has many advantages over late-ploughing, that include lower costs, greater uniformity of land preparation, greater moisture conservation, early and uniform decomposition of organic matter and hence readily available nitrogen at the time of planting.

A good tilth is more easily obtained and conditions are favourable for water planting. For these reasons early-ploughing is recommended whenever possible. Fields can normally be considered “late-ploughed” if the ploughing is done from June to August.

This is when the soil is dry, allowing little decomposition of organic matter before the following season’s rains.

Ridging
Tobacco should be grown on ridges or beds for two major reasons:

◆ To promote good surface drainage

◆ To provide a good environment for early growth of the crop.

This is because the soil on the ridges penetration. Initially, ridges should be relatively low (20 cm) and broad with flat tops to allow for maximum percolation of early rains.

After the crop has established, ridges can be built up by re-ridging. This would only be done after good rains have brought the soil to field capacity.

Re-ridging removes weeds in the furrow and on the sides of the ridge and promotes better surface drainage.

Ridge spacing
Variations in ridge spacing and plant spacing on the ridge affects yield and quality of the tobacco produced. Where planted tobacco), it is suggested that the ridge spa smaller plants are expected (late plantings), an average ridge spacing of 115 cm will be satisfactory.

In-row spacing of 54 spacing will reduce the size of the plants and individual leaves on the other hand, increase the proportion of heavy-bodied leaf grades

Spacing and resultant crop populations

A plant population of 14 500 plants/ha will give good yields and quality

◆ For more information, contact Kutsaga Research Station’s Crop Productivity Division on telephone (04) 575 289-94 or toll-free, 0800 4511 or Email: [email protected] or visit Kutsaga Research Station.