If you have ever lived in the country or ventured outside of a city in in the spring time you will have seen one of the most common agriculture practices that is used by man. The sight and smell of freshly tilled or cultivated soil is for some the true beginnings of spring and is a herald for better weather to come. But what many people are not aware of is that the seemingly benign and earth friendly practice of tillage actually has very troubling and only recently understood detrimental effect on the soil.
Soil is a living entity composed of millions of bacteria, fungi, plants and animals and tillage is like a hurricane, volcano, and forest fire all rolled up into a annual event. Could you imagine if we had to experience those events year after year like clockwork. The basic structures that hold the soil together and give it is ability to grow food are damaged and destroyed every time the soil is ripped up by tillage
There are a few key things that tillage negatively effects in the soil that I will be covering here. They include
Soil Carbon/Organic Matter
Soil Carbon/Organic Matter
Exactly what it sounds like soil carbon is the carbon that is present in the soil. Carbon is placed in the soil through decomposition of dead plant matter that is in and on top the soil. Research done in Morris, MN shows that as much carbon was lost to the atmosphere as was placed in the soil by the wheat crop the previous year just 19 days after it was moldboard plowed. Soil carbon is always being slowly released into the atmosphere but tillage as the effect of “poking the fire” and accelerating the process.
As more carbon enters the atmosphere is adds to the already growing pool of carbon that is put there through other industrial activities and potential worsens the climate change issues we face. The loss of carbon and organic matter in the soil reduces the water and nutrient holding capacity of the soil which makes it less productive. A study done on corn fields in Kentucky showed a remarkable organic matter difference between no till and tilled fields. In the fields that were tilled they lost about half of their organic matter content. The study also showed a larger increase in organic matter in fields that received additional nitrogen that were no tilled compared to the tilled fields. When 84 kg/hectare of nitrogen were applied to a no till field the organic matter content of the soil went up .73% while the same amount applied in the tilled field only increased organic matter by .13%. The difference in the amount of organic matter in each soil tells us about the overall health of the soil. The fields that were no-tilled were better able to utilize the nitrogen and thus more organic matter was put into the soil from more bountiful and healthy crops.
Its no secret that when you remove the vegetation from the top of soil that some if it will be blown or washed away from wind and rain. What I think few people are aware up is the scale of the erosion that can take place is astounding. For example studies in Latin America have shown that anywhere from 10-60 tons/hectare/year are lost every year to erosion. When you take into account the soil regeneration rates of around 250-500 kilograms/hectare/year it becomes obvious this soil loss is not sustainable. Erosion from tillage is not just a problem in 3rd world countries but also here in the US and other Western countries as well. Under conventional tillage up to 44 tons/hectare/year will be lost off of industrial managed farm fields located in the US. The real kicker to the problem of soil erosion is that studies have show that the most fertile soil is eroded away first. This leads directly to land being abandoned for being unproductive and infertile. The loss of productive land forces farmers and ranchers to move to marginal lands which were originally left alone because they were unstable and prone to erosion.
Soil compaction occurs due to the large amounts of vehicle and animal traffic on agriculture fields. Some compaction will occur from any agriculture practice but tillage destroys the structures of the soil that resist the compaction forces that are being placed on the soil. One of the many things that tillage is used for is to lighten and dry the soil from spring planting. The implication of this is that the fields will be tilled when the soil is wet. When soil is wet it is many times more susceptible to compaction from tire traffic. The formation of a plow plan or traffic pan layer will form directly beneath the edge of the tillage implement and tires of a tractor. This layer can be difficult to to break up without the use of heavy cultivators or moldboard plows. But when you use heavy cultivation you damage the structure needed to prevent compaction and without careful management compaction can enter a negative feedback cycle that will cause it to keep happening. Under natural conditions plant roots and soil organisms will help mitigate the impacts of compaction in the soil but under a tillage system there is too much soil disturbance for them to assist
Last but not least we have what I feel to be the least understood and most confusing of the effects of tillage. Initial yields after tillage are documented to be 10-100% after tillage because of release of nutrients that comes with combining of mixing the soil layers. But quickly enough the loss of of organic matter and the erosion that is inevitable with tillage begins to depress the crops yields after just a few years. Plant productivity is very dependent on the health of the soil which is destroyed by tillage. The only reason we don't see a crash in crop yields in tilled fields is because of the large amounts of nutrients that are applied to them every year. Synthetic nitrogen fertilizer now supplies about half the worlds crop nutrient needs and at least 1/3 of the worlds protein is synthesized from nitrogen and hydrogen using the Haber-Bosch process. Another essential nutrient called phosphorus is also being mistreated by convention tillage. As water runs off of tilled fields it takes soil particles and phosphorus with it downstream and eventually to the ocean where it is essentially lost. This phosphorus must then be replaced in the form a fertilizer that is derived from mined phosphorus. Like any mined element there is only so much of it and we are running out of phosphorus. Scientists theorize that we have only until about 2030 until we hit peak phosphorus after which production of phosphorus will go down and cost will rise. Without easily available phosphorus there will be no way to grow food at the the rate we currently do. No phosphorus means lower food production and we will not not be able to feed the world without it.
It has become clear to the agriculture science community that continuous conventional tillage is something that we can't continue and expect to produce food at the rate we need to sustain our current and future populations. If tillage on a large scale continues we will till ourselves out of good fertile land and crop yields will fail to provide enough to feed the world. Luckily this is not a forgone conclusion and there are solutions available to us right now. Using a variety of of practices like no-till cropping, planting windbreaks and using cover crops we can drastically reduce the damage we do to the soil. It has even been shown that we can reverse the trends of organic matter loss, carbon release into the atmosphere and nutrient leaching. With sustainable agriculture we can responsibly manage our farms and ranches and gardens in a way that will feed the world in for many years to come.