Replenishing Soil Nutrients on a Organic Farm
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Replenishing nutrients on an organic farm is not a complicated task but it does take long term thinking and planning of what you will be growing for the next few years. With industrial agriculture adding nutrients to your fields is a easy as buying and applying fertilizer from the agriculture supply store. With organic farming it gets a bit trickier than simply spraying a chemical. You have to learn more about how soil recovers and recycles nutrients naturally and then figure out a way to give the soil what it needs to do that.
Nutrient Recycling Basics Nutrient recycling takes place when something dies and is left to decompose on or beneath the soil surface. Organic materials are broken down by two main families of organisms, bacteria and fungi. The bacteria are a critical part of nutrient cycling because they take broken down organic matter and convert the materials nutrients into available nutrients for more plant growth. Without a constant stream of available nutrients provided by bacteria many plants would have stunted growth and limited overall success. In native undisturbed ecosystems the nutrient levels stay fairly static with little bits leaving by leaching out with water and in the bellies of critters. But on the same end you get nutrients being deposited by inflows of water and by animals dying and leaving waste in the ecosystems as they travel. But when you look at agriculture especially industrial agriculture you see massive influxes of nutrients coming in and going out according to the seasons. While this can grow some impressive crops it is detrimental to the landscape and the natural nutrient cycling that is essential for healthy soils and crops. To transition from a conventional system of agriculture to an organic one requires that you establish the natural nutrient cycling of the soil. Now this can take a few seasons and you will see reduced yields and crop success during this time. It can be compared to someone trying to quit smoking. The soil has become addicted to those easy chemical fertilizers so why bother trying to recycle your own nutrients. When you stop adding them into the system there is a temporary slump in productivity until the microbes in the soil are built back up to healthy levels. Replenishing Soil Nutrients Organically The two common methods to replenish soil nutrients on an organic farm are manure and cover crops. Now manure is the oldest form of nutrient replenishment on a farm and it is still an essential tool to maintaining soil nutrition. There are general guidelines put out by agriculture researchers that are great for telling you how much manure you will need to add depending on the type of manure. 
http://www.cals.ncsu.edu/waste_mgt/smallfarms/Manure.pdf
As you can see above in the table, different types of waste will give you different amounts amount of available nitrogen. Information like this is essential in telling you what you need to maintain fertile soil on a organic farm. You will also need to perform frequent soil nutrient tests to tell you how much you will need to apply.
Manure can be applied in a one of three ways. The two more conventional ways involve some sort of manure hauler and a spreader. It will then either be flung out and spread in a dry form or sometimes sprayed out in a liquid form depending on the source. Most manure would be spread in a dry form and one of the exceptions to this is dairy cow manure. Now this approach is effective but it can be costly in both your time and in fuel required to run your machinery. A more organic approach would be to fence off areas where manure will need to be applied and then let the cattle, horses or other stock graze off crop residue. This approach does require some forethought and you have to get the stock out in the fall to really get some manure on the field before spring. This technique also requires that you actually have some sort of stock on your farm to do this with. The second method to replenish soil nutrien ts is through the use of green manure cover crops. Now green manure is a systematic planting and incorporation of the green growth of plants into the soil. Green manure can be typically divided up into two different groups of plants based on how they return nutrients to the soil. Nutrient Scavengers The first group is composed of plants that have deep dense roots systems. These plants are great at scavenging out trace nutrients that have leached down into the soil profile. The plants then bring those nutrients up into their stalks and leaves. Before the plants can produce seed they are cultivated into the soil and all the nutrients are then slowly released into the soil and made available for the next crop. This is a great way to provide micronutrients needed by plants in small amounts without applying fertilizer. Some examples of species that you could plant to scavenge nutrients would include small grains, cereal rye, triticale, rapeseed, annual ryegrass and oilseed radishs. Legumes The next group of plants that could be used as green manure crops would be legume plants. Legumes are a special type of plant that with the aid of microorganisms can fix or remove nitrogen from the atmosphere and incorporate it into the soil at their roots. With these plants it is essential that the entire plant be cultivated into the soil to get the most nitrogen possible. 
This list is not a complete one for the types of legumes that you can use for a cover crops in a organic farm. Most people that use cover crops like this will use a combination of the nutrient scavengers and legumes to create a better overall cover crop. To learn more about legumes, cover crops and other methods of nutrient cycling check out the sources in this article and other posts here on the Green Living Library.
Sources: https://pubs.ext.vt.edu/2906/2906-1374/2906-1374.html https://www.rhs.org.uk/advice/profile?PID=373 http://www.ext.colostate.edu/mg/Gardennotes/244.html |
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