Wind-row composting Turned wind-rowsWind-row composting consists of placing the mixture of raw materials in long narrow piles called wind-rows (Plate 7) that are agitated or turned on a regular basis (NRAES, 1992). The turning operation mixes the composting materials and enhances passive aeration. Typically, the wind-rows are from 90 cm high for dense materials such as manures to 360 cm high for light, voluminous materials such as leaves. They vary in width from 300 to 600 cm. The equipment used for turning determines the size, shape and spacing of the wind-rows. Bucket loaders with a long reach can build high wind-rows. Turning machines produce low, wide wind-rows.

Wind-rows aerate primarily by natural or passive air movement (convection and gaseous diffusion). The rate of air exchange depends on the porosity of the wind-row. Therefore, the size of a wind-row that can be aerated effectively is determined by its porosity. A wind-row of leaves can be much larger than a wet wind-row containing manure. Where the wind-row is too large, anaerobic zones occur near its centre. These release odours when the wind-row is turned. On the other hand, small wind-rows lose heat quickly and may not achieve temperatures high enough to evaporate moisture and kill pathogens and weed seeds.

For small- to moderate-scale operations, turning can be accomplished with a front-end loader or a bucket loader on a tractor. The loader lifts the materials from the wind-row and spills them down again, mixing the materials and reforming the mixture into a loose windrow. The loader can exchange material from the bottom of the wind-row with material on the top by forming a new wind-row next to the old one. In order to minimize compaction, this needs to be done without driving onto the wind-row. Wind-rows turned with a bucket loader are often constructed in closely spaced pairs and then combined after the wind-rows shrink in size. Where additional mixing of the materials is desired, a loader can be used in combination with a manure spreader.

There are a number of specialized machines for turning wind-rows that reduce the time and labour involved considerably, mix the materials thoroughly, and produce a more uniform compost. Some of these machines attach to farm tractors or front-end loaders, others are self-propelled. A few machines can also load trucks and wagons from the wind-row.

It is very important to maintain a schedule of turning. The frequency of turning depends on the rate of decomposition, the moisture content and porosity of the materials, and the desired composting time. Because the decomposition rate is greatest at the start of the process, the frequency of turning decreases as the wind-row ages. Easily degradable or high N mixes may require daily turnings at the start of the process. As the process continues, the turning frequency can be reduced to a single turning per week.

In the first week of composting, the height of the wind-row diminishes appreciably and by the end of the second week it may be as low as 60 cm. It may be prudent to combine two windrows at this stage and continue the turning schedule as before. Consolidation of wind-rows is a good wintertime practice for retaining the heat generated during composting. This is one of the advantages of wind-row composting. It is a versatile system that can be adjusted to different conditions caused by seasonal changes.

With the wind-row method, the active composting stage generally lasts three to nine weeks depending upon the nature of the materials and the frequency of turning. Eight weeks is usual for manure composting operations. Where three weeks is the goal, the wind-row requires turning once or twice per day during the first week and every three to five days thereafter.

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