Two pass no-till is an oxymoron; however, it is a term used, and a BM practice (in our area), allowing participants to access USDA and Ecology money as an incentive to try no-till for erosion control. I have never been a fan of the practice, feeling that success would be erratic and it may be an inoculant against no-tilling. That question is still not answered.
For nearly 40 years I have listened to researchers talk about what it takes for maximum yields, whether it be a conventional tillage, or no-till system. There are many factors that go into high yields but two are always part of the list. They are:
---Place seed in soil (not residue). Most crop cultivars grow through and among residue without any growth issues as long as the seed is placed in soil. All the issues I have heard about have been with seed being in close contact with decaying residue.
---Cotyledons need to emerge within three days of each other. Thirty-five plus years ago I first heard a speaker (and several since), mention that seed can lay in the ground for some time; however, when conditions allow the seed to germinate, cotyledons emerging within three days of each other comprise 90% of a crops yield. You can imagine how this be the case. All plants compete for sunlight, nutrients and water. If one gets a jump start of four or more days, that plant develops roots and leaves before the other plants in it's sphere of influence, and takes the lion share of everything. The plants emerging later will be starved to some extent, and can actually degrade the overall quality of the crop.
Operations associated with 2 pass no-till systems in our area just don't meet the two parameters mentioned above, of seed placement for timely emergence. A lot of N is lost in a surface application of fertilizer unless the operation can be timed with a rain, --this results in most fertilizer being shanked 4-6 inches into the ground. Shanked fields are rough and cloddy and residue, if there is any, is left clumped. Drills normally used for conventional tillage systems are then rolled over these rough fields dropping seed erratically in/on the ground and residue. If the stars line up right you can get a decent looking crop started; however, most look bad. To improve emergence, harrows or packers have been allowed and still qualify for two-pass operations. In my mind these operations then become reduced tillage operations. Reduced tillage systems do reduce water erosion in a lot of cases, but still, they are not nearly as effective as a high disturbance one pass no-till drill system, in either plant emergence or soil erosion.
---Place seed in soil (not residue). Most crop cultivars grow through and among residue without any growth issues as long as the seed is placed in soil. All the issues I have heard about have been with seed being in close contact with decaying residue.
---Cotyledons need to emerge within three days of each other. Thirty-five plus years ago I first heard a speaker (and several since), mention that seed can lay in the ground for some time; however, when conditions allow the seed to germinate, cotyledons emerging within three days of each other comprise 90% of a crops yield. You can imagine how this be the case. All plants compete for sunlight, nutrients and water. If one gets a jump start of four or more days, that plant develops roots and leaves before the other plants in it's sphere of influence, and takes the lion share of everything. The plants emerging later will be starved to some extent, and can actually degrade the overall quality of the crop.
Operations associated with 2 pass no-till systems in our area just don't meet the two parameters mentioned above, of seed placement for timely emergence. A lot of N is lost in a surface application of fertilizer unless the operation can be timed with a rain, --this results in most fertilizer being shanked 4-6 inches into the ground. Shanked fields are rough and cloddy and residue, if there is any, is left clumped. Drills normally used for conventional tillage systems are then rolled over these rough fields dropping seed erratically in/on the ground and residue. If the stars line up right you can get a decent looking crop started; however, most look bad. To improve emergence, harrows or packers have been allowed and still qualify for two-pass operations. In my mind these operations then become reduced tillage operations. Reduced tillage systems do reduce water erosion in a lot of cases, but still, they are not nearly as effective as a high disturbance one pass no-till drill system, in either plant emergence or soil erosion.
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