Primary symptoms

Poor land preparation can lead to poor, uneven or weedy stands. Soil crusting can reduce seedling emergence (especially in soils high in clay and silt).

Lesser leveling can improve plant establishment

Summary

Preparing your land prior to sowing should have the following aims.

• It should create a soil structure that encourages the seedlings to emerge rapidly and uniformly and allows the young plants ready access to the vital resources of nutrients, water and aeration. Both full tillage (also called conventional or clean) and minimal tillage systems have this aim, but minimal tillage limits soil disturbance to the surface layers or just a shallow slot for each crop row. Because minimal tillage often uses light machinery that can be taken into the field when the soil is wet, as perhaps after a previous rice crop, it has the prime advantage that it commonly shortens the time between successive crops/rotations. This can be critical for maximising yield per year.
• It should aim to incorporate any additives such as lime, compost, farmyard manure and chemicals for plant nutrition and pest control and, depending on location, may incorporate residues remaining from previous crops.
• It should control weeds, pests and diseases.
• It should aim to shape the land so that irrigation water can be applied efficiently and drained effectively and so that waterlogging is avoided or minimised. This may involve leveling, preparation of furrows, beds and so on.

If you have little or no equipment or have limited access to equipment for timely and quality land preparation, perfect seedbeds may not be possible, particularly if the farming system uses flood or furrow irrigation.

That system depends on multiple tillage operations and leveling with construction of borders to channel and contain the irrigation water. It may be beneficial to use minimal tillage or zero tillage or to spend time developing a permanent raised bed system. If raised beds are used, the process of forming the soil is more complex. Here the field is formed or reformed into long leveled raised beds, 60-80 cm wide with two or three defined planting rows, the beds separated by irrigation/drainage channels. However, in later years when the bed structure is well established and undamaged from the previous crop and residues/mulches are thick, only the predefined planting rows need to be cultivated, similar to minimal tillage farming on flat land.

Problems of land preparation

• Before sowing, note the size of clods remaining after cultivation. If they are dense and greater than 5 cm in diameter, they could cause variations in seeding depth or physically prevent seedlings from emerging. Fix the problem now.
• Before sowing, check for signs of waterlogging. Are there wet patches in low areas perhaps slightly green with algal growth or if dry, a silty crust on the soil surface? Waterlogging can cause death of seedlings and tillering plants.
• Before sowing, check where the soil moisture is by scratching into the surface soil until the colour darkens or the soil feels damp. Is it too dry for germination?
• Before sowing, check if the residues from the previous crop that remain on the surface are thin enough to allow your planter to penetrate and sow at uniform depth. Are the incorporated residues bulky so that they create large air gaps in the surface soil that could preclude uniform planting?
• A week or two after planting, check for crusting. Dig up seedlings where crusting occurs or where emergence is variable. If unemerged seedlings are bent and twisted and have long yellow leaves, they failed because they could not penetrate the crust.
• Are many seeds dry and not germinated? The soil was too dry at planting.
• Is the field weedy? If the weeds are larger than the crop seedlings, the weeds were either not killed by pre-sowing cultivations or the cultivations were done too long before sowing, allowing weeds to grow back.

Causes of poor seedbeds

• Cultivation occurred when soil was too wet, resulting in clods.
• Cultivation occurred when soil was too dry and/or there was too much secondary cultivation, causing loss of structure. If this was followed by excess rain or irrigation a surface crust is formed.
• Soil structure is poor because of salinity or sodicity.
• Residues were not incorporated sufficiently or excesses were not removed prior to land preparation.
• The gap between cultivation and sowing was too long and the seedbed dried.

How to improve your seedbed

• Secondary tillage: Reduce clod size by secondary tillage. But beware of overdoing this if the soil is very dry as this could destroy soil structure and result in crusting later. Also develop guidelines for when to cultivate in relation to moisture content.
• Minimize crusting: Minimize crusting by reducing the number of secondary cultivations that might be pulverizing the soil, and leave some crop residues in the surface soil layers. If sprinklers are available, sprinkle-irrigate prior to seedling emergence to soften the crust.
• Residues: If reduced tillage practices follow high-yielding rice, maize or soybean crops, remove excess residues so seeds can be sown accurately at uniform depth. Alternatively, use equipment that can sow accurately into heavy crop residues.
• Timing: Time cultivations so they are not too long before planting. Aim to give the crop seedlings an advantage over germinating weeds and weed regrowth.
• Reduced tillage: Use minimal or zero tillage so that all operations can be done at the optimum time and completed quickly. This can avoid overworking the soil and consequent loss of soil structure, avoid clods, and avoid wasting water because a minor proportion of bare soil is exposed to the drying air.