Hi there!
You know, there's lots of good information about the dryland topic scattered in this forum, and several attempts at unifiying them all. I hope you find this one useful.
What is DRYLAND?
It's a piece of arid
land that receives no
water from outside. No river, no dams, no pipes bringing water from afar. Only some rainfall and whatever water accumulates in the ground,
More strictly, we speak of dryland when we don't even have a well.
Water is needed for growth. In drylands, water is scarce, therefore growth is slow. In very arid places, this growth is so slow that it can't cope with erosion. The good news is that weeds are less common and that funghi are less aggressive towards our crops.
But let's be honest, with little water, there's little yield.
RAIN PATTERNS.
In drylands, all water depends on rainfall, so it is crucial to understand its patterns.
First, we have to know
how much water precipitates every year on average. That's the maximum growth we could achieve if we were able to capture all the water. It also limits the amount of biomass that can be sustained per area. The maximum biomass is achieved when decay, which depends on the current biomass, is balanced with growth, which depends on water and sunlight availability. As an example, a plum orchard requires 400-450mm of average rainfall per year, fail to provide it, production will suffer.
Then we need to know
when it rains. Plants require more water in their vegetative phases, when they are growing faster, and less water when they are fruiting or dormant. When it is raining, the surface layer is wet. After the rain, the water is slowly seeping
underground, depending on the texture of the soil (clay is slow, sand is fast). A few days after the rain the surface might be dry, but there's water still seeping at some depth. Plants with a
root system that reaches that depth can still take that water.
Finally, we need to know
how it rains. There are basically two modes: desertic and rainy. In desertic mode, rains are strong and few, provoking a flood-draugh cycle that erodes the land and increases runoff water. In rainy mode, rains are gentle and frequent, allowing many seeds to germinate. The rainy mode is caused by large forested areas in vegetative state. For example, a healthy Mediterranean climate is desertic in summer and winter, rainy in spring and automn, so it's semi-desertic.
By observing a wild landscape we might learn about the rainfall pattern in our region. The size of the old forests will tell us how much it rains on average: are they dense or sparse, do they form dense canopies or are they some scattered
trees with some bushes? The shape of the hills will tell us how it used to rain. Are they rounded and soft, meaning a rainy pattern, or are they angular as in deserts? Maybe the area has been deforested in recent decades and the pattern has changed and it is on the process of becoming a desert. About seasons, you can ask the locals if data is not available, they sure know when it usually rains.
COMMON STRATEGY: ADAPTATION
The native plants are already adapted to the
local climate and soil characteristics. Most of them are useful in some way or another. Including a few natives in the growth plan is almost always a good idea. However, in arid zones the edible natives are few and we might need to add some of exotics for eating.
Life is tenacious, and given the opportunity, it will find ways to stay alive. Regardless the weather and climate, there's always a plant that can thrive. Moreso, some plants can be breeded to thrive in the land as it is, provided they can at least survive. For plants that don't even survive, it is possible to create more gentle microclimates where they might survive, and stress them looking for traits that will allow them survive in the land unhelped.
Check
Joseph Lofthouse '
Landrace gardening', for a modern/ancient approach on how to adapt plants to the specifics of the land.
https://permies.com/wiki/162247/Landrace-Gardening-Joseph-Lofthouse
I want to stress that landracing plants will be benefitial regardless of irrigation and rain patterns, but they will adapt to the way we grow them. Better to adapt the plants for the method we want to follow.
COMMON STRATEGY: MINIMIZE RUNOFF WATER
One of our aims is to maximize growth in the land. Letting rainwater wash away is not helping, therefore the more slowly water escapes the land, the better.
Here we better listen to the rainwater harvesting guru,
Brad Lancaster: Slow it, spread it, sink it.
https://permies.com/wiki/51855/Rainwater-Harvesting-Drylands-Brad-Lancaster
- Slow it. Water moves roughly following the slope (for a more thoroughly explanation, read
this guide). Water needs time to infiltrate in the ground. If the slopes are too steep, runoff water will go away fast. So we need to force water to move following the longest path downwards (a 1% slope is good). A terrace does just that, and it also provides a wide platform to work on.
Keyline design also leads runoff to the ridges of the hills instead of the valleys, with less disruption. A
swale is an on contour trap for the water, but it needs to consider the overflow. For more hydrated landscapes, Keylines have to be supplemented with several ponds to prevent water plumes from collapsing the ditches.
- Spread it. Runoff water collects in the lowest zones, the valleys, and forms streams. These streams are like razor knives eroding the soil, so we need to blunt their edges. Wherever a stream can be formed, we can reduce its eroding power by spreading the water sideways. Swales spread it laterally, while dams spread it vertically. A check dam limits the flow of the stream within its capacity. Dams, however, must be strong to stand the push of the stream and even then, they may need maintenance. A preferred method is the lateral
pond, that fills with the stream water when the stream level is high
enough: it doesn't need to endure the strength of the stream and yet it takes away some of its mass.
- Sink it. Groundwater moves very slowly, compared to runoff water, so the faster it sinks the less water that will escape as runoff. The best surface for absorbing water is a healthy soil full of growing plants, followed by a healthy soil covered with mulch. If those are not available, we might create percolating ditches or ponds; these are the same as normal ditches and ponds, but they are designed to sink water instead of retaining it, featuring a porous surface. By sinking water, we are also recharging the aquifers.
Brief note: when conducting earthworks for increasing water retention, bear in mind that the very first years it will affect the amount of running water in streams that are fed with runoff water, which may cause damage to current ecosystems if done at large scale. In a few years things will rebalance.
COMMON STRATEGY: REDUCE STRESS
Once the water is in the ground, we need to preserve it as best as we can so it is available for growing. The two biggest factors in stressing the water storage are
heat and wind, both to the soil and to the plants. In cold climates, when water is frozen it is not lost, but plants can't use it for growing either.
- Shading cloths can reduce heat over crops. So can do shading trees.
- Plants in a slope move heat from the base to the top.
- The atrium cooling effect can be used to cool an enclosed square zone, it can be achieved with hedges.
- Morning sun is cooler than evening sun, so shaded areas in the evening are cooler: East wall is cooler than west wall.
- Wind breaks made with trees not only reduce the drying effect of winds, but also provide some moisture.
TO IRRIGATE OR NOT TO IRRIGATE?
Ok, in drylands we don't have access to other water than what rains, but that doesn't mean we can't irrigate. We may irrigate if we are able to capture and store sufficient rainwater for our crops. We may store small quantities in tanks, for domestic use (drinking, nursery, pots) and we may store it in ponds for larger applications. If we place these storages at a higher level than where we need to use the water, then we won't need to use
energy to move the water, it will fall by gravity. Stored water
should be protected from direct sunlight and heat. If we place them underground, then there will be less evaporation and algae.
In rainy mode we may skip irrigation if we provide a catchment area large enough for our crops. For example, if we want to grow a crop that demands three times the water that usually falls, then we just need to provide these crops an area three times larger than usual, so all the water that falls in this area goes to the crops. In this aspect, a rainy drylands can be like a wetlands with fewer plants. We may still want to irrigate if we want to concentrate crops in a single compact field, or if we need to control the amount of water we are providing in every stage.
In desert raining mode the story is different. Even if we manage to put every drop underground, the water will seep slowly but unceasingly. One month after the last raining event, the surface will be dry, only plants with long root systems will reach the fading water. After two or three months without real raining or irrigation, plants will find water no longer. Draught tolerant plants follow one of these strategies: Some plants go dormant during the day, and they will refuse to grow even when watered; some will enter a kind of summer hibernation and will look like dead, but will reactivate after the hot season; some will sacrifice their upper side, leaving only the
roots alive; some will produce thousands of seeds very fast and then die (yes, weeds). Plants adapted to draught are either short lived or slow growth.
If the soil is heavy (clayey), when it is completely dry it turns into a compacted brick that's hard to dig, refuses to absorb water and kills any tender stem. Only woody plants may stay alive in such conditions, like rosemary and thyme.
Seeds that require a few weeks of constant humidity might not even sprout in desert raining mode.
STRATEGIES FOR UNIRRIGATED DESERT DRYLAND
Here we have a few days when it rains heavily and we need to put all that water in the soil, then store it as best as we can, so that whatever we are growing can find that water when they need it. Plants need deep root systems to reach seeping water for longer.
Perennial plants must be adapted to draught.
-
Shallow tilling. This is a traditional method in my country, not suitable for light soils. The surface of the field is tilled to allow water to infiltrate while removing every other plant that may take water for itself. When it rains, the tilled earth absorbs water quickly. The seedling are planted in rows (no direct seeding!), at wide distances for increasing catchment area. When the surface dries out it forms a crust that must be tilled again. This tilled crust makes a good isolant that prevents moisture from evaporating. The problem is that the soil loses fertility and has to be supplemented with fertilizers.
-
Mulching. When available, mature
compost is the best mulching material, but any other mulch will do. Chopped and dropped plants work, although they barely decompose, they mostly dissecate and turn to ashes. Stone mulching may work in hot climates if properly shaded, otherwise they may burn the plants.
-
Zai pits. These are holes with their own catchment area. Being a few centimeters below ground helps the plants to reach a bit deeper, where there's more water. The hole also collects and retains water, allowing it to seep just where the plant is planted. It needs to be fertilized too.
-
Agroforestry. Trees have
deep roots that find water several months after the last rains. In addition, they provide much needed shade that reduces surface evaporation while increasing air humidity in the area. So, vegetables might be grown below fruit trees to benefit from their protection. It's like using a natural shadow clothing, with an extra fruit yield. The trees need to be pruned heavily to prevent excessive shadowing.
- Experimental techniques like sunken hugelkulture beds. Here I tell of my
experience with them
https://permies.com/t/152917/permaculture/sunken-bed-time-tips.
- There's no water for compost piles. Organic material exposed to sun will just dissicate and turn into ashes. Any composting is done by bugs underground.
- Cactus and succulents are desert plants adapted to desert raining pattern, but they also create conditions for it to remain a desert. They don't evapotranspirate like most plants, they have an extensive but shallow root system and really slow growth, so they aren't good at building soil, infiltrating water in the soil or creating rain. Don't overuse them in semi-desertic climates.
STRATEGIES FOR IRRIGATED DESERT DRYLAND
Assuming we can store some rainwater in ponds or tanks, but not enough for watering at leisure. It has to be used wisely.
- Seed trays can be irrigated to produce seedlings and saplings can be irrigated while getting established.
- For encouraging root development, we let the surface to dry before watering again.
- It's best to irrigate early in the morning, when the soil is coolest. A hot soil will lose more water by evaporation.
- Shading and wind protection are still relevant, for they reduce watering needs.
- Mulching has to be done with mature compost or inert matter, since unfinished compost will absorb water for its own process.
- Irrigation can be done with ollas (only moistens the area around the clay pot), with drip irrigation (expensive, may clog with hard water, but very efficient otherwise), and sprinkling (consumes more water but increases fertility and it's reliable). Flooding irrigation is not reccomended as it consumes too much water, but sometimes it's the only technique available.
- Even if we can cultivate plants that are not tolerant to draught, using mostly draught tolerant plants will make our life easier.
- Get to know whether your plants are active, dormant or hibernating (dropped the leafs in summer). If they are hibernating there's no use in irrigating them. If they are dormant, then they need some moisture for staying alive, but they will refuse to grow or fruit. When there's plenty of water, the plant will stay active, growing and consuming water. Beware not to awaken your plants if you can't provide them water for the rest of the dry season!
STRATEGIES FOR UNIRRIGATED RAINY DRYLANDS
As already said, when the amount of precipitation is lower than what our crops demand, the catchment area has to be increased so every plant is given a surface that captures enough water for its needs. There are a few ways to do this: When the water is captured outside the cultivated area it is called macro-catchment, and micro-catchment otherwise.
Since rains are not too strong, there's less need for capturing runoff water, but still, any of the techniques used for desert dryland can be used here. Other suitable techniques are:
-
Ponds. A percolating pond above the cultivated area will hydrate the field below steadily without the need for irrigation. Percolating ponds also work to recharging the aquifers. Regardless the amount of precipitation, if we capture more water than it is consumed, eventually the aquifers will refill. With high water table, permanent water may resurface and trees may be able to reach the water saturated layer, allowing a faster yearly growth, and more diverse species.
-
Swales. Plants growing inside a swale will get more water than those growing above it.
-
Rock horseshoe. This is the same as a swale, but for individual plants. The small wall of rock collects debris and moisture around the plant.
-
Mulching. Mulch works by keeping the moisture in the soil, however, composting material should be avoided since it will steal water and rainwater may not reach the soil layer when precipitation is too low.
POT GARDENING: WICKING POTS VS NORMAL POTS
In drylands, not much water can be spared to irrigate pots, but that doesn't mean we can't have pots.
Wicking pots are known for their water savings: Since the surface remains dry, not much water is lost in evaporation. Being constantly irrigated, the substrate doesn't lose its moisture ever. As any pot gardener knows, having your substrate to dry easily leads to a death spiral of overwatering and underwatering. To prevent rotting, the water in the deposit must remain clean and protected from the sun. A properly designed wicking pot should not develop funghi, which is a risk when the substrate stays wet for too long.
Here I am using a very simple immersion pot, which is not safe as it may develop funghi
But traditional terracotta pots also have an advantage in hot climates. A problem with pots is that they don't have a constant temperature, unlike grounded plants, and it might get excessively hot for the roots. A watered unglaced terracotta will evaporate water through the sides of the pot, cooling the roots.
---***---
This guide will be edited as needed, based upon feedback.