Agronomist notebook: Here is one of the best rotational crops

After harvesting their main crops, many farmers wonder what to plant next for an effective rotational programme.

Well, wonder no more because you can grow canola plant, which gives an excellent rotational programme since it offers cultural crop protection and enhances soil fertility.

Canola can be grown after cereal crops such as maize, wheat and barley, breaking the pest and disease life cycle.

In Narok, Nakuru and Nyeri, among other areas, many farmers are embracing the crop. Canola plant is bred from rapeseed and has lower levels of glucosinolates.

It belongs to the brassica family that grows from three-to-five feet tall and produces pods from which seeds are harvested and crushed to make canola oil and meal.

The plant produces small, yellow flowers that mature into seeds that produce the oil. Upon ripening, the seedpods turn brown.

The demand for the vegetable oil, which has low saturated fats, is high, making the crop highly marketable.

In Kenya, various varieties do well in well-distributed rainfall. The canola plant does well in a wide range of soils that are well-drained and have moderate soil fertility.

Soil pH should be less than 5 to avoid phosphorus fixation. The crop matures after three months.

The crop requires nitrogen and phosphorus as the primary nutrient. However, a successful fertiliser programme is based on the knowledge of the soil nutrient level and requirements.

The land should be prepared to a fine tilth during the dry period to allow weeds and other residues to decompose.

Proper land preparation is necessary, as this helps control weeds before planting. The vegetative nature of the crop normally smothers weeds.

To plant, make shallow drills of 2-3cm at a spacing of 20-30cm, and then sow the seeds. Broadcasting method can also be used.

PREVENT WIND DAMAGE

For optimum growth, the plant requires 15-200C. However, low temperatures are usually a prerequisite to flowering.

The crop is primarily grown under rain-fed irrigation, thus timely planting is ideal as moisture stress during flowering leads to reduced yield. In dry areas, irrigation can also be done to obtain optimum yields.

The crop has a large taproot, which cracks into the soil, improving the drainage. It is also known to control disease during decomposition of root residues, hence can be used in various cropping systems such as intercrops, cover crops, rotational crops and trap crops.

Once canola is established, it does not require much attention other than spraying to control pests and diseases when necessary.

The crop is, however, affected by pests and diseases such as diamond back moth. The pest feeds on the leaves between the large veins and midribs.

This can be controlled by the adoption of integrated pest and disease management, which reduces the use of the chemicals and allows the build-up of the beneficial microorganisms.

Windbreakers like agroforestry trees such as grevelia or maize crop should be planted on the edge of the farm to minimise seed loss.

This helps prevent wind damage, which happens as the stems sway, resulting in the shattering of pods causing seed loss.

Harvesting is done when the crop appears brownish, and the majority of the seeds are in the firm dough stage with moisture content of about 25-45 per cent.

Before harvesting, the crop should be well-dried to ensure smooth harvest, which can be done using combine harvesters that also thresh the seeds. Harvested seeds should be dried or kept cool in a storage room that is well-aerated.

While seeds are used to extract oil (which one can do on the farm), the cake makes quality livestock feed ingredient. The canola meal is also used as a high-quality organic fertiliser.