There are various agricultural residues that are produced in both small- and large-scale farms. In Kenya, most of the farm left overs includes; rice straw, rice husks, maize copes (corn stover) and wheat straws. The residues in many farms are used as fodder for animals, landfill or others will end up being burnt during land preparation. In areas where agroforestry is practiced, dead leaves, branches are considered as residues. As farmers approach the maize harvest season, it is essential to consider practices that will enrich the soil for the next planting season. One such practice is residue retention, which involves leaving crop residues on the field after harvest.
Key Farm Residues
- Leaves
- Maize/corn stover
- Sugar cane stover
- Rice husks
- Rice straw
- Wheat straws
- Uprooted weeds
- Overgrown and dead vegetables
After-Harvest Management of Residue
After harvesting, the field is often left with stalks, leaves, and other plant materials. Proper management of these residues is crucial for maximizing their benefits to the soil. Here are some key steps to consider:
- Assess the Residue
Before deciding on a management strategy, assess the amount and type of residue left on the field. Maize typically leaves a substantial amount of residue, which can vary depending on the variety and yield. Understanding the volume and composition of the residue helps in planning its retention, degradability and management effectively.
- Decide on the Method of Retention
Once you understand the nature and volume of your farm residues, it is important to make the choice on the retention approach. This is guided by understanding the period it will take your residues to completely decompose. There are various methods to manage crop residues, including mulching, composting, and incorporation into the soil. For maize, direct retention by leaving the residues on the surface or lightly incorporating them into the soil are common practices. Each method has its own benefits and should be chosen based on soil type, climate, and farming practices.
- Timing of Residue Management
The timing of residue management is crucial. Ideally, residues should be managed immediately after harvest to prevent them from interfering with subsequent farming activities. This also allows for maximum decomposition time before the next planting season. Timely management ensures that the residues do not hinder soil preparation activities like plowing or tilling.
- Ensuring Even Distribution of Residue
Uniform distribution of crop residue across the field is essential for achieving consistent soil benefits. Uneven distribution can lead to patchy decomposition and variable soil fertility. Here’s how to ensure even distribution:
Use Proper Equipment
Modern combines and other harvesting equipment are often equipped with choppers and spreaders that can evenly distribute residue across the field. Ensure that these mechanisms are well-maintained and properly adjusted. Chopping the residues also enhances efficient decomposition.
Manual Redistribution
In some cases, especially on smaller fields, manual redistribution might be necessary. Use rakes or other tools to spread the residue evenly. This labor-intensive method can be particularly effective in ensuring that all parts of the field receive equal benefits from the residues. Manual spreading can address areas missed by machinery and ensure a thorough distribution.
Avoid Piling
Avoid creating piles or windrows of residue, as these can decompose unevenly and create areas of excessive organic matter, which might hinder seedling emergence in the next planting season.
How to Speed Up Decomposition of Residue
Accelerating the decomposition of crop residues can help in quickly releasing nutrients into the soil, making them available for the next crop cycle. As a farmer, you should use the following techniques to speed up this process:
Chopping and Shredding; Breaking down the residue into smaller pieces increases the surface area exposed to decomposers, thus speeding up the decomposition process. Equipment like rotary mowers, use of pangas and slashers, or flail choppers can be used for this purpose. These machines cut the residues into finer pieces, which decompose faster compared to whole stalks and leaves.
Moisture Management; Microbial activity, which is essential for decomposition, is heavily dependent on moisture. Ensuring that the soil and residues are kept moist, especially during dry periods, can significantly enhance decomposition rates. Monitoring soil moisture levels can help in deciding when to irrigate to maintain an ideal environment for microbes. However, the residues themselves helps to trap and conserve moisture, which is fixed to the soil.
Adding Decomposition Agents; Introducing organic matter decomposition agents, such as compost inoculants or microbial cultures, can accelerate the breakdown of crop residues. These agents enhance the microbial activity in the soil, facilitating faster decomposition.
Benefits of Residue Retention
Residue retention offers numerous agronomic and environmental benefits. Here are some of the key advantages:
- Enhanced Soil Fertility
As crop residues decompose, they release essential nutrients back into the soil, such as nitrogen, phosphorus, and potassium. This natural fertilization process reduces the need for synthetic fertilizers, promoting sustainable farming practices. Over time, the continuous addition of organic matter from residues can build up soil fertility and improve crop yields.
- Improved Soil Structure
Residue retention contributes to the formation of soil organic matter (humus), which improves soil structure. Better soil structure enhances root penetration, water infiltration, and overall soil health. Organic matter binds soil particles into aggregates, creating a crumbly texture that is ideal for plant growth.
- Moisture Retention
Residues on the soil surface act as a mulch, reducing evaporation and helping to retain soil moisture. This is particularly beneficial during dry spells, ensuring that crops have a more consistent water supply. During residue decomposition, the soil will be covered and protected from direct sunlight hence moisture and nutrients will be preserved for the next planting cycle.
- Erosion Control
Crop residues provide a protective cover for the soil, reducing the impact of raindrops and wind. This helps to prevent soil erosion, preserving the topsoil which is crucial for crop growth. Topsoil is rich in nutrients and organic matter, and its preservation is vital for maintaining soil fertility and productivity.
- Weed Suppression
A layer of crop residue can suppress weed growth by blocking sunlight and preventing weed seed germination. This natural weed control method reduces the need for herbicides, promoting a healthier and more balanced ecosystem.
- Fixing of beneficial soil micro-organisms
Humus attracts vital micro-organisms such as azotobacter and warms which helps in fixing of vital macro and micro nutrients into the soil and crops. Microorganisms are also critical in increasing the volume and to aerate the soil.