Farm update week of February 20th; Caring for the soil, part 2

Winter came back a bit since our last update, and limited the amount of work we could do. But things are supposed to warm up again by the end of the week.

We planted out first batch of peas, under a row cover and a plastic covered tunnel. The peas were pre-sprouted in a can of warm water. Pre-sprouting helps seeds to germinate if the soil temperature is too cool or warm. Once the seeds start growing, they will continue to do so even if the soil temperature is not optimal. We used lots of bent rebar pins hammered into the soil to hold down the tunnel, in the hope that it won’t blow away. But since our farm is in a particularly windy spot, we will have to wait and see. I still don’t have pictures of this, but I’ll get them up soon, if it works!

In my last post on caring for the soil, I mentioned that there is an excess of potassium in the soil. Organic matter typically contains a large amount of potassium in it relative to other elements; potassium is used to build the structure of plants, and thus materials such as wood chips, straw, and leaves contain a lot of potassium, while the other more mobile elements have been leached out or moved by the plant into roots and seeds. So adding organic matter to our soil will increase the relative imbalance of potassium. This is a problem, because organic matter is very important to soil health. It helps the soil form a good crumb structure, hold water and nutrients from leaching away, and most importantly, feeds the microorganisms, which protect and feed the plants. The more life there is in the soil, the better, and organic matter is the fuel for this life.

To add organic matter without unbalancing the soil, we will be growing lots of cover crops, particularly rye, sorghum, oats, and clover. These plants will loosen the soil, protect it from the sun and wind, and add organic matter to the soil when they decompose, all without adding any more potassium. This is also more sustainable then importing organic matter from other soils to their detriment. Legume cover crops, such as clover, vetch, and field peas, also fix nitrogen from the air with the help of symbiotic bacteria. Eventually, we hope to grow all our own nitrogen in this manner and avoid purchasing nitrogen fertilizer.

Avoiding the importation of organic matter will also help us avoid any potential contaminants. Recently, new herbicides have been developed that do not break down in the composting process; they can contaminate straw, manure, hay, and grass clippings, and when applied to a farm or garden, can inhibit the growth of broadleaf plants for as many as seven years.

We recently borrowed a broadfork to assess its performance on our farm. A broadfork is a larger version of the standard garden digging fork, with specially shaped long tines, a wide crossbar, and two handles. For pictures and video of a broadfork in action, here is a link to the version made by Valley Oak. I’m very happy with it; using it allowed us to loosen our hard soil a foot down, without the smearing and destruction of soil life and structure associated with tilling or plowing. Using it is also more enjoyable then using a tiller. Over time, the roots of the cover crops mentioned above will fill the soil voids produced by the broadfork, making the improvement permanent and creating a deep, rich topsoil.

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Caring for the Soil, Part 1

Ultimately, farmers are not in the business of raising crops; they are in the business of growing soil. Top soil is the beginning and end of farming. Soil is also an immensely complex system, varying from place to place, even over short distances, and containing a stunningly intricate system of life. Chemical, structural, and biological processes must all be fostered if a farmer wishes to improve his soil.

On our farm, the soil is a fairly heavy clay, which tends to be dense and sticky when wet and hard when dry. It has low organic matter and a slightly alkaline pH.

In a soil, the base cations,  (Calcium, Magnesium, Potassium, and Sodium) should be in a certain ratio; Calcium should take up the vast preponderance of the available “storage” (cations are stored on humus and clay particles) followed by magnesium, potassium, and sodium in that order. While Calcium can be as high as 70%, magnesium should be around 15%, and potassium should be a mere 2-5%. (Sodium should be always lower then potassium, and is not essential.) If these ratios are off, plant growth, soil life, and even soil texture will suffer.

It should be pointed out that this is just one of many different theories on soil health. Some farmers target other ratios, though always with Calcium taking the largest share. And many farmers don’t look at ratios at all; instead, they add a sufficient amount of each nutrient for the upcoming growing season. After much research, I’ve decided to follow the Albrechtian ratios as given above, since they were developed with a focus on the health of the whole system.

It is also important to realize that plants don’t “eat” as we do. There are a number of nutrients they need from the soil; Nitrogen, Phosphorus, Calcium, Magnesium, Potassium, Sulfur, Zinc, Copper, Iron, Manganese, and Boron are the most important. However, taken all together they make up a very small percent of a plant; most of the plant’s bulk is make of carbon, hydrogen, and oxygen drawn from the air and water.

In any case, if the chemistry of a soil is corrected, the soil will come to life biologically.

On our farm, the potassium is much too high. This is a complicated problem. For one thing, just like salt in soup, you can’t easily get a nutrient out of the soil. For another thing, most organic matter is high in potassium relative to the other nutrients it contains, so importing lots of organic matter will further imbalance this soil. The other cations are in fairly good shape. We are slowly resolving the problem by adding some gypsum every year. Gypsum a compound of sulfur and calcium. The calcium will replace the potassium, which will then combine with the sulfur to create potassium sulfate. Potassium sulfate is water soluble, so it will move deeper into the soil, away from the root zone. (The sulfur is also a necessary nutrient in the soil.)

Nitrogen is also necessary in fairly large amounts every year; but since it is fundamentally tied to the organic matter content of the soil, I will discuss it in the next post.

The soil started out with slight deficiencies in boron, copper, and zinc. These nutrients are tricky because they are needed in fairly small amounts, and an overdose can damage the soil. For instance, in the topsoil of a whole acre, there needs to be four pounds of boron; no more and no less. This translates into a tiny sprinkling of borax on each bed. These nutrients can not be added without careful soil testing.

In my next post, I will discuss our strategy for the organic matter and microbial life in the soil.

Using Water Efficiently; from Ollas to Huglekultures to Lithic Mulch

We live in a high plains desert, where water is a problem. Denver only gets fifteen inches of precipitation in an average year, and much of this evaporates without infiltrating deeply, or comes as snow in the winter. On the other hand, in many years there is too much rain in the early spring, and summer thunderstorms can drop an inch of rain in a few hours, causing disastrous flash floods. In this post I will focus on how to cope with too little water; many of these strategies work both ways. I’m not going to discuss rainwater harvesting or greywater; both are very interesting and promising techniques, but are outside the scope of this post. There are lots of complicated details in regard to each; hopefully I will be able to give each of them a separate post in the near future.

Our focus is on using water wisely to grow annual vegetables and edible perennials, not ornamental gardens.

Also, I’m only giving a brief summary for each of the techniques below. As we implement them on the farms this summer, I will write a more in depth post on each with photos of our work.

Drip-line/ Soaker hose

These are a much more efficient way of using water then spray irrigation, because they don’t wet the leaves and soil surface. This also helps to prevent fungal disease. However, they are expensive, and tend to wear out over time. They are easy to damage with gardening tools. Also, they only work with clean, high pressure water, so they can’t accept rainwater or greywater.

Ollas/ Bucket Irrigation

Ollas are an ancient irrigation method. Small clay jugs or pots are buried near plants and filled with water. Depending on the moisture level in the soil, more or less water seeps out. Clay pots can be pricey. A cheaper alternative is a five gallon bucket with a small hole drilled in the bottom. Water will slowly dribble into the soil, soaking in deeply without wetting a large surface area. Buckets could be moved around to different beds, unlike ollas, which are immovable, but they lack the sensitivity to soil conditions gained with porous ollas. Delis and bakeries are good sources for free food grade buckets.

Wicking Beds and Containers

Wicking beds contain a subsurface reservoir of water, generally formed by a layer of gravel, which slowly wicks up through the soil to the plant roots. They eliminate surface evaporation and nutrient leaching, and keep the soil evenly moist, avoiding under and over watering. This is very important for some plants, such as tomatoes and lettuce. They are labor intensive and expensive to build. A cheaper variation is a wicking container built on the same principle. They can also be built from 5 gallon buckets.

Dew Catchment

This is the least tested of the ideas on this list. The basic principle of dew catchment is to insulate a smooth reflective surface, thus isolating it from ground heat at night. This lowers its temperature because of radiant cooling to the night sky. Once the temperature of the surface falls to the dew point, condensation collects and is funneled into a container or directly into the ground. Dew catchers can also improve the utilization of light rains, turning a surface dampening shower into a ground soaking drip of water on one spot. If you have any experience with dew catchment in Denver, let me know!

Mulch

Organic mulch is a double edged sword from a water utilization standpoint. A thick layer of wood chips, leaves, straw, or other organic matter can retain moisture in the ground, and works well in combination with ollas, bucket irrigation, drip lines, and soaker irrigation. However, mulch can soak up a surprising amount of spray irrigation or rainfall before any reaches the ground. Since roots usually don’t grow in the mulch layer, this water is wicked away and evaporated into the air. However, when correctly applied, mulch can go a long way towards drought proofing a garden and has many other benefits.

Lithic Mulch

Native Americans in the southwest used rocks as mulch in their gardens, which held moisture in the soil, and also increased the infiltration of light rains by shedding water rapidly into the soil. They may also capture moisture from warm air condensing on the cool lower rocks during the day. However, they can overheat plants and complicate the management of the garden. (For some plants, the extra heat is an added benefit.) In the wild, plants seem to grow lushly in and around talus piles at the base of cliffs.

Soil Management

Raising the organic matter percentage in the soil increases the amount of water that can be stored for dry times. A foot of rich soil can hold three inches of water. Also, deeply loosening soil can increase rooting depth and water infiltration. Double digging can achieve this on small sites, and chisel plowing on big ones. Hugelkultures, which are buried mounds of woody debris, achieve both these objectives. In this climate, sunken hguelkultures are probably better then the mounded types seen elsewhere. Mini hugelkultures can be dug into the ground for individual plants. Soil can also be contoured to catch water running down slopes and retain irrigation water, but this is a complex topic for another article.

Plant Spacing

Plant spacing can work both ways. A dense, Biointensive style planting can be lightly irrigated to create a moist microclimate under the leaves, slowing evaporation and speeding growth. However, wide spacing of large plants gives each plant access to more water, since the plant will react by growing a larger root system in the larger soil volume available per plant. In the end it depends on the objective. If one has a lot of room and hardly any water, then wide spacing is probably best. If one has only a little room and wants to use their available water to best effect, tight spacing will do well.

Fertilization

All else being equal, a plant in a fertile soil can get by with less water then one in an infertile soil. In a fertile soil with all the minerals in balance, a plant has to absorb and transpire less water to obtain its needed nutrients. This does not always apply, and fertilizer should not be overused. Also, woody plants should not be fertilized when they are water stressed.

Pruning

How a plant is pruned makes a big difference in how much water it uses. This is a very complex topic, and I would advise you to do your own research.

Transplants

A flat of transplants can be placed in the shade and watered more efficiently then the same seeds planted out in the eventual bed. This also has the effect of expanding the size of a small garden, since a bed can continue growing crops while the new transplants get going. On the other hand, some plants such as squash can sustain damage to the root system when they are transplanted, which reduces their ability to search for water. Large seeds should be pre sprouted until the root tip is just emerging, then planted. This helps conserve water and avoids root damage.

Timing

If plants can be started a few weeks earlier, when there is still abundant water available, things will be much easier later on. Cold frames, row covers and transplants are all valuable here. Also, deep waterings once a week are much better then shallow ones daily.

Variety

Some varieties are better at searching for water then others, and some types of vegetables are simply more drought resistant. For instance, purslane grows wild here in the summer with very little water, whereas lettuce is always thirsty and wilts in the heat. All else being equal, older varieties are more likely to be breed for tolerable performance in sub optimal conditions, but this is not always the case.

Windbreak/ Shading

For plants that tolerate the shade, an over story crop or shade structure that blocks the wind and direct sun can make a huge difference in the amount of evaporation losses.

Capillary Connection

Soil that is too loose can keep water from moving upwards through the soil. If necessary, the ground should be firmed around new transplants and seeds.