1. SEED DRILLS
Seed may be sown by broadcasting, drilling or planting. Broadcasting means scattering the seed by hand over the land as evenly as possible using a fertiliser distributor or air from a specially adapted aircraft. Broadcasting is used for grass seeds and small cereal seeds such as wheat. After sowing, the land is harrowed with a light spike harrow to cover the seeds with soil. Broadcasting is not satisfactory for the larger seeds such as maize and soyabeans because the seed is difficult to cover and tends to lie on the soil surface. Broadcast seed covers the ground well, but can be uneven and a higher seed rate needed. While it is not possible to carry out inter-row cultivations, or any cultivation after seed has been broadcast, as long as the seed is sown on clean ground, the higher seed rate helps to overcome and smother the growth of weeds.
Figure 1: A single row, one-man seed drill. Note the marker on the right of the machine which marksthe position of the next row. This type of drill can be used for market gardens and small scale cropping.
Seed Drills and Planters sow seeds in lines. The seed rate and distance between lines is determined by the setting on the drill. In general, seed drills are used for grass seeds and small cereal seeds. These are sown in lines which are spaced closely together. Planters are used for large seeds such as maize and potatoes which are grown in lines that are more widely spaced. The advantages of drilling seed are that a lower seed rate is needed and inter-row cultivations can be carried out on the growing crop.
Seed drills and planters can be pushed by hand, pulled by a horse, ox or tractor, or mounted on the three-point linkage of a tractor.
Tractor Seed Drills
The Seed Drill in Figure 2 is made into different size, according to the farmers needs. There are small discs at the bottom of the machine called coulters which help to break up the soil and make a small furrow which the seed falls into. The Row spacing can be altered from a minimum of 180mm upwards. Higher spacings can be obtained by blocking off some of the seed tubes. The manufacturers of all seed drills supply instructions and charts for setting the drills to sow different seed rates.
Figure 2: A Seed Drill
This type of drill can be used to sow wheat, soybeans, sorghum, cotton, groundnuts, grass seeds, etc.
The Seed Drill shown below is mounted on the 3-point linkage of the tractor and the drill is lifted out of the ground at the end of each row. As the drill is lifted out of the ground, the flow of seed is automatically cut off.
Figure 3: A seed drill mounted on a 3-point linkage of the tractor
The Combine Seed Drill
This type of drill sows both the seed and fertiliser at the same time. The picture below shows the drill in operation. In the picture below one can see the pipes which are first in line from the tractor are the fertiliser lines and the pipes which follow directly behind are the seed lines.
Figure 4: A combine seed drill
The Planter shown below is mounted on the tractor linkage and plants 4 rows of both fertiliser and seed. The large hoppers hold the fertiliser and the smaller hoppers hold the seed. This type of planter is used to sow large seeds such as maize.
Figure 5 and 6: No till planters
Source: radzimagripower Source: radzimagripower
No-till planters can plant into a field that has not been ploughed or disced. This ensures that the organic matter left from the previous crop protects the soil from erosion and water run-off as well as holding soil moisture. The organic matter decomposes and provides nutrients for the crop. This tillage system is extremely good for the soil and is more cost-effective as the farmer only needs to go over the land once. However pest and disease pressure may be greater and the very good spray programme will have to be implemented to reduce pest and disease pressure. The picture below shows how little soil disturbance there is from a no-till planter.
Figure 7 and 8: No-till planting into the previous crops mulch (left) and a well established crop ofmaize growing in a thick bed of mulch which was planted as a cover crop (right)
Source: radzimagripower Source: plantcovercrops.com
Figure 9: shows a land that has been planted using the no-till method, this is soya beans planted intomaize stova
Strip till planters
The planter shown below is a planter that has been adapted to sow into land that has not been ploughed or cultivated. Two discs run in front of the planting units and they cut and loosen a strip of earth where the seed is planted. The fertiliser is placed behind the second disc. Any crop grown in rows can be planted with this machine, but the land must be free from weeds and chemical weed control may be required for the growing crop.
Figure 10: A Strip till planter, planting in a lightly disced land
Figure 11: The strips created by the strip-till planter
Planters can sows seeds and treat them with an inoculant at the same time. The inoculant is sprayed onto the seeds after they have left the seed chute, and any surplus inoculant falls onto the soil and is not wasted. This type of planter is used to sow legumes such as soybeans, groundnuts, beans, etc.
This machine ridges up the soil and plants the seed potatoes. Three operators sit on the seats, dropping the potatoes into the ground at regular intervals.
Figure 12: Fully automatic planters are made, and these require only one man on the tractor
These are machines used to sow seeds at exact intervals in the row. The idea is to use high quality seed placed at exactly the right intervals in the row which does away with the necessity of thinning out plants after germination. These machines are used for root crops such as sugar beet, turnips, and for market garden crops like onions, cabbage and carrots. The seeding mechanism consists of a
rubber belt with holes in it which allows the seeds to fall through. The belts are changed for different seed sizes and seed rates. These machines sow each seed individually at a constant depth in the soil.
Figure 13: A precision planter
Table 1: Calculating the In-Row Spacing for Seeds –the distance between the plants in the samerow.