Introduction
The yield of a crop of rice is dependent upon many obvious factors: irrigation, fertilization, weeding, pest and disease control. One of the less obvious but equally important factors is land preparation. Because proper land preparation promotes a good environment for seed/soil contact (which will promote rapid crop growth while reducing competition from weeds), it is imperative that land preparation be thorough and timely. This chapter describes and justifies the steps necessary to prepare lowland soil for a successful growing season.
I. Brushing and Clearing
Bard preparation in inland valley swamps begins with a through brushing and clearing Encourage the farmer to begin with the larger stumps and bushes, since grasses and other weeds grow back very quickly and are best left until just before the first plowing. Bushes and tree limbs should not be left to overhang the edges of the paddies. Rice does not grow well in the shade and insects thrive in cool, moist areas. The initial brushing and clearing should be completed about one month before planting.
II. Repairing Water Control Structures
Next, clean and repair all water control structures - irrigation gutters, drains, and sluice gates. Remove weed that have grown in the channels and dig out accumulated silt and clay. The flow of water through the channels is impeded by weeds and sediment, and their capacity is greatly reduced. Repair dikes that may have eroded, paying particular attention to the headband and peripheral (irrigation) gutters. Check all sluice gates for signs of wear; if any threaten to wash out, repair them now. Remember: it is always easier to make repairs and alterations to the water control system before you plant.
III. Plowing and Puddling
After the water control structures have been cleaned and repaired, plowing may begin. Flowing is done in inland valley swamps for several reasons:
- Weed Control (weeds are destroyed and prevented initially from competing with rice seedlings)
- Incorporation of Organic Matter (weeds and crop residues such as straw and stubble are incorporated into the soil, where they become converted into plant nutrients through decay)
- Transformation of Surface Soil into a Puddle (for ease in transplanting)
- Establishment of a Reduced Zone (increases the availability of some nutrients by maximizing contact between rice root hairs and soil particles)
- Levelling (during plowing the soil can be moved around until the plots are level, thus improving water control)
- Formation of a Flow Pan (repeated plowing to a certain depth will create an impervious hard layer, or plow Far., which will reduce water losses and mineral losses through leaching)
To be most effective, plowing must be done thoroughly and timed properly. In inland valley swamps, the ideal schedule calls for two plowing and one puddling. Timing these operation correctly is very important.
1) First Plowing
The first plowing, or deep plowing, should be completed 2-3 weeks before transplanting begins. There are several reasons for such an early start:
- to protect seedlings against the adverse effects of harmful substances generated by decomposing organic materials
- to allow seedlings to utilize the nitrogen rich ammonium (NH4) released during the decomposition process
- to spread out the work load for the farmer (thorough plowing is very hard work and is best done a little bit at a time)
Flood the plot for several Jays before plowing to soften the soil and make the work easier. On the day of plowing, drain off excess water. Using a hoe or shovel, turn the soil to a depth of 15-20 cm (6"-8") Begin near the edges of the plot (so you can repair the bunds if necessary) and work toward the center. Keep the plot flooded after the first plowing until transplanting. If the plot is allowed to dry out, 20-700 kg of valuable nitrogen could be lost into the air through a process known as denitrification depending on the soil, its previous cropping history and other factors. Note: Many farmers will at first be reluctant to plow 2-3 weeks in advance of transplanting. The traditional practice in many areas is to wait until the seedlings are nursed and almost ready to plant before starting to plow. Encourage farmers to complete the first plowing before parsing their rice. The 2-3 week lead time will give the organic matter sufficient time to decompose, and the toxic substances released during organic matter decomposition will dissipate before the seedlings are planted.
2) Second Plowing
The second plowing should take place 7-10 days after the first plowing. Break up the softened clumps of soil and incorporate straw, stubble, and weeds that may have germinated. Remove large roots that will not decompose, as well as large stores. Lower the water level in the plot during the second plowing to reveal high spots which will need to be leveled. Re-check the water control system and make minor adjustments as needed.
3) Puddling.
Puddling should take place,-10 days after the second plowing and one day before transplanting. Puddling is usually done with bare feet (and draft animals, in areas where they occur). Bush poles are often used to help maintain balance and to break up remaining soil clumps. Puddling further incorporates germinating weeds, facilitates levelling, and breaks down the soil structure into a soupy mud suitable for transplanting. If a basal application of fertilizer is intended, broadcast the fertilizer just before puddling so that it will be well mixed into the soil. After puddling, the soil will be ready for transplanting.
IV. Methods of Plowing
Flowing may be accomplished in several ways:
- plowing by tractor is generally rot suited for inland valley swamps because tractors cannot move easily from plot to plot without destroying water control structures. Furthermore, in flooded soils tractors often are simply too heavy. Initial cost and operating costs are high.
- plowing by roto-tiller (2-5 horsepower) is gaining acceptance in many parts of the world, despite high initial cost and maintenance problems. In broad swamps with large plots, the roto-tiller can be extremely effective and economical. Roto-tillers cannot be used in recently-developed swamps containing many stumps and large roots.
- plowing by animal is extensively practiced with excellent results in most of Asia, but less frequently in Africa (where the se of draft animals is less widespread in general). Most
- draft animals are able to work only 3-4 hours per day without supplementary feeding, end they require considerable care.
- plowing by hand, though tedious and time-consuming, is the major method of plowing inland valley swamps throughout most of Africa. Hand plowing requires the farmer to spend many hours standing in water and thus facilitates the spread shistosomiasis.