Tillage operations are broadly grouped into two types based on the time
Types of Primary Tillage
Depending upon the purpose or necessity, different types of tillage are carried out. They are deep ploughing, subsoiling and year-round tillage.
Deep ploughing turns out large sized clods, which are baked by the hot sun when it is done in summer. These clods crumble due to alternate heating and cooling and due to occasional summer showers. This process of gradual disintegration of clods improves soil structure. The rhizomes and tubers of perennial weeds (world’s problematic weeds viz., Cynodon dactylon and Cyperus rotundus) die due to exposure to hot sun. Summer deep ploughing kills pests due to exposure of pupae to hot sun.
A deep tillage of 25-30 cm depth is necessary for deep rooted crop like pigeonpea while moderate deep tillage of 15-20 cm is required for maize.
Deep tillage also improves soil moisture content. However the advantage of deep tillage in dry farming condition depends on rainfall pattern and crop.
It is advisable to go for deep ploughing only for long duration, deep rooted crops. Depth of ploughing should be related to the amount of rainfall that it can wet.
Hard pans may be present in the soil which restrict root growth of crops. These may be silt pans, iron or aluminium pans, clay pans or -man-made pans. Man-made pans are tillage pans induced by repeated tillage at the same depth. Root growth of crops is confined to top few centimetres of soil where deep penetration of roots is inhibited by hard pans.
For example, cotton roots grow to a depth of 2 m in deep alluvial soil without any pans. When hard pans are present, they grow only up to hard pan, say 15-20 cm. Similarly, vertical root growth of sugarcane is restricted due to hard pans and it is not compensated by horizontal spread. Subsoiling is breaking the hard pan without inversion and with less disturbance of top soil. A narrow cut is made in the top soil while share of the subsoiler shatters hard pans. Chisel ploughs are also used to break hard pans present even at 60-70 cm. The effect of subsoiling does not last long. To avoid closing of subsoil furrow, vertical mulching is adopted.
Tillage operations carried out throughout the year are known as year-round tillage. In dry farming regions, field preparation is initiated with the help of summer showers. Repeated tillage operations are carried out until sowing of the crop. Even after harvest of the crop, the field is repeatedly ploughed or harrowed to avoid weed growth in the off season.
Lighter or finer operations performed on the soil after primary tillage are known as secondary tillage. After ploughing, the fields are left with large clods with some weeds and stubbles partially uprooted.
Harrowing is done to a shallow depth to crush the clods and to uproot the remaining weeds and stubbles. Disc harrows, cultivators, blade harrows etc., are used for this purpose.
Planking is done to crush the hard clods to smoothen the soil surface and to compact the soil lightly. Thus the field is made ready for sowing after ploughing by harrowing and planking. Generally sowing operations are also included in secondary tillage.
Layout of Seedbed and Sowing
After the seedbed preparation, the field is laid out properly for irrigation and sowing or planting seedlings. These operations are crop specific. For most of the crops like wheat, soybean, pearl millet, groundnut, castor etc., fIat levelled seedbed is prepared. After the secondary tillage, these crops are sown without any land treatments. However, growing crops during rainy season in deep black soils is a problem due to ill-drained conditions and as tillage is not possible during the rainy season. Broadbed and furrows (BBF) are, therefore, formed before the onset of monsoon and dry sowing is resorted to.
For some crops like maize, vegetables etc., the field has to be laid out into ridges and furrows. Sugarcane is planted in the furrows or trenches. Crops like tobacco, tomato, chillies are planted with equal inter and intra-row spacing so as to facilitate two-way intercultivation. After field preparation, a marker is run in both the directions. The seedlings are transplanted at the intercepts.
Layout of Seedbed
The tillage operations that are carried out in the standing crop are called after tillage. It includes drilling or side dressing of fertilisers, earthing up and intercultivation.
Earthing up is an operation carried out with country plough or ridge plough so as to form ridges at the base of the crop. It is done either to provide extra support against lodging as in sugarcane or to provide more soil volume for better growth of tubers as in potato or to facilitate irrigation as in vegetables.
Intercultivation is working blade harrows, rotary hoes etc., in between the crop rows so as to control weeds. Intercultivation may also serve as moisture conservation measure by closing deep cracks in black soils.