It's that time of year!! We, along with our neighbors have started making fallow that will be seeded to WW this fall. There are as many ways to do this as there are farmers in the area.
I walked into this field the other day (not ours) and smelled the pungent aroma of fresh tilled soil, and also I felt a significant difference in humidity while traversing from the cultivated area into the non cultivated area. It was a bit startling. There is a lesson here! (actually 5 that comes to mind.)
1--Soil moisture: Moisture has been exposed by the cultivator and is being evaporated out of the soil at a rapid rate, raising the humidity. Some documents I have cruised indicate approximately 0.5" lost per trip. (Many years ago, I checked this on our operation and found that we had lost ≈0.5"+ in three operations of cultivating, weeding, harrowing to set up the fallow.)
On this field(pic), the lack of residue (standing or not) allows air movement along the surface, removing the high humidity(100%) interface between soil an the atmosphere, --if you see dirt there isn't enough residue to protect the soil. This high humidity layer is constantly being replaced until the soil can no longer provide the moisture. Research shows that most of our soil moisture is lost through EVAPORATION (83%+) from the soil surface. The best moisture saving practices keep the surface COOL and CALM. This loss can not be eliminated, but it can be dramatically slowed.
2--Soil Temperature: Destroying residue that covers the soil raises soil temperature. This in turn increases the evaporation from the soil. Research shows a 20 degrees difference between covered and uncovered soil. Our own testing verifies this.
1--Soil moisture: Moisture has been exposed by the cultivator and is being evaporated out of the soil at a rapid rate, raising the humidity. Some documents I have cruised indicate approximately 0.5" lost per trip. (Many years ago, I checked this on our operation and found that we had lost ≈0.5"+ in three operations of cultivating, weeding, harrowing to set up the fallow.)
On this field(pic), the lack of residue (standing or not) allows air movement along the surface, removing the high humidity(100%) interface between soil an the atmosphere, --if you see dirt there isn't enough residue to protect the soil. This high humidity layer is constantly being replaced until the soil can no longer provide the moisture. Research shows that most of our soil moisture is lost through EVAPORATION (83%+) from the soil surface. The best moisture saving practices keep the surface COOL and CALM. This loss can not be eliminated, but it can be dramatically slowed.
2--Soil Temperature: Destroying residue that covers the soil raises soil temperature. This in turn increases the evaporation from the soil. Research shows a 20 degrees difference between covered and uncovered soil. Our own testing verifies this.
3--OM is being destroyed. Tillage introduces oxygen (air). By combining OM(fuel), oxygen, and heat(from ground and atmosphere), so the biological furnace is stoked and the OM is destroyed, converting to elements that include nitrogen(N), and CO2.
4--CO2: --is released into the atmosphere. When soils are not disturbed, a relative balance of gases is established in the soil profile. The two most notable are oxygen and CO2. Cultivation, while adding oxygen to the soil releases CO2 from the soil. There is some exchange of these gases all the time through soil interaction with plant growth and biological activity; however, soil disturbance accelerates this phenomena. The more intense the disturbance, the greater the gas exchange. Conventional fallow, requiring several tillage operations, releases CO2 to the atmosphere several times during that fallow period. Minimizing mechanical soil disturbance, and building soil structure through plant diversity is the best way to provide oxygen to the soil, and control the release of CO2 into the atmosphere.
5--N: There is no question that N is produced by this accelerated biological furnace, and standard soil tests acknowledge this by calculating an expected amount of N, from a given level of OM.
The stability of this N seems to be the question, and I am totally confused at this point. Nitrate N is water soluble and goes where the water goes. Ammonia N ties to the soil particles and goes where the soil goes. Both of these forms evolve over time. This has been known for many decades. A high percentage of these forms end up in the public waters. From what I'm reading, our crops are only using about 45% of the N that we apply. That's pathetic, costly to our operations and the environment.
Now "Organic N" is becoming a subject of discussion. What is this, and what distinguishes it? From what I am reading, Organic N is suppose to be stable and available to plants. It's not suppose to disappear except through plants or the physical removal of the organic matter from the field, --but information is all over the board on this subject and my understanding is minimal. Please enlighten!
4--CO2: --is released into the atmosphere. When soils are not disturbed, a relative balance of gases is established in the soil profile. The two most notable are oxygen and CO2. Cultivation, while adding oxygen to the soil releases CO2 from the soil. There is some exchange of these gases all the time through soil interaction with plant growth and biological activity; however, soil disturbance accelerates this phenomena. The more intense the disturbance, the greater the gas exchange. Conventional fallow, requiring several tillage operations, releases CO2 to the atmosphere several times during that fallow period. Minimizing mechanical soil disturbance, and building soil structure through plant diversity is the best way to provide oxygen to the soil, and control the release of CO2 into the atmosphere.
5--N: There is no question that N is produced by this accelerated biological furnace, and standard soil tests acknowledge this by calculating an expected amount of N, from a given level of OM.
The stability of this N seems to be the question, and I am totally confused at this point. Nitrate N is water soluble and goes where the water goes. Ammonia N ties to the soil particles and goes where the soil goes. Both of these forms evolve over time. This has been known for many decades. A high percentage of these forms end up in the public waters. From what I'm reading, our crops are only using about 45% of the N that we apply. That's pathetic, costly to our operations and the environment.
Now "Organic N" is becoming a subject of discussion. What is this, and what distinguishes it? From what I am reading, Organic N is suppose to be stable and available to plants. It's not suppose to disappear except through plants or the physical removal of the organic matter from the field, --but information is all over the board on this subject and my understanding is minimal. Please enlighten!
I was under the impression you had moved away from summer fallow. Why do you summer fallow when you have the equipment to do no till? I agree with you that tillage is very destructive to the soil environment. For educational purposes though I think it is worth noting to those that are unfamiliar with dryland farming here that seed zone moisture is actually better preserved--most years--by the dry dust mulch created by tillage.
ReplyDeleteNo, --fallow is still part of our rotation. My dream with DS was/is to remove fallow because of its destructive nature. It is a very well studied fact that fallow is slowly destroying the productivity of our soils, and has a negative impact on water and air quality annually from natural climate events. Fallow needs to become part of our history and not be part of our future.
ReplyDeleteYour question about why we still fallow and mention of the dust mulch, deserves a post of it's own.