|Path alongside the allotments looking down the south facing slope.|
Although I grow crops in north south rows, I have put in paths from east to west at right angles to the slope. The paths have been made as mini ditches and soil has been taken out and put onto the growing areas to raise them. The mini ditches are aligned more or less with the contours across the allotment. Water will flow at right angles to the contours soaking in as it does. Some surface water will flow into the ditches and spread out. I have filled the ditches with woody shreddings which will soak up some of the water and prevent it from evaporating creating a reservoir of stored water.
Espaliers planted on the top of the raised bank.
This allows surface rain water to be spread out evenly along the path, slowed down and soaked into the soil. Although irrigation is not a particular priority in the UK climate, we still have to consider the effects of leaching and soil erosion.
Raising the level of the soil, creating banks on the downside of the slope and planting espaliered fruit trees or soft fruit along the east west raised soil aids in the slowing down of water (mass flow) through the soil. As the water is slowed, it allows dissolved nutrients to be taken up by plants before it is lost though leaching.
As plant nutrients are soluble minerals they will be leached slowly as the water flows to the bottom of the slope. I have planted comfrey at the bottom of the slope to catch as much leached nutrient as I can. Their deep roots will absorb much of the available nitrogen and any potassium and phosphorus that is available. The leaves and stems of the comfrey can then be composted, made into comfrey liquid or put into the worm bin to recycle the nutrients.
It is all about slowing the mass flow of water through the soil. This will slow leaching, allow more time for uptake of soluble minerals; capture eroded soil particles, enhance water filtration and provide more opportunity for upward water capillary action for plant growth.
My compost heaps are at the top of the slope so that any leachate that they produce will flow down the slope and into the allotment soil. In a similar way, I have planted perennial nitrogen fixing legumes along the top of the slope so that any nitrogen they fix will flow naturally into the allotment top soil. I will be planting perennial legumes alongside the fruit trees and bushes on the banks alongside the paths so that nitrogen will flow with the water into the growing areas.
|Compost bins at the top of the slope so that leachate will flow into the allotment.|
Laburnum and lupins planted at the top of the slope so that nitrogen they fix will
flow into the allotment growing areas.
In the UK there is often too much water flowing through the allotment. It is necessary to put in some kind of drainage to prevent waterlogging. I have dug out a trench at the bottom of the allotment and filled it with stone sieved from the top soil. The stone was covered with paving slabs to make a path alongside the hedge.
|Drainage ditch under the slabs. Path is at the bottom of the slope.|
During the driest months in summer, the soil is covered by mulches to reduce evaporation and the trench Hugelkultur further slows the soil water and retains it as a reservoir that is accessible to plant crop roots.
So slopes can be very useful.