[Update: 5/22/14] --- Summary of a Summary ------ The bottom Line:
a)--Where rainfall goes (average over 10 years of a two year moisture cycle): 1% deep penetration, 4% runoff, 12% transpiration through the crop, 83% evaporation off soil surface.
b)--In a wheat/fallow rotation, the fallow year provides only 34% more moisture for the winter crop. In short, we lose the equivalent of 2/3 of one years precipitation growing one winter crop.
c)-- That long term study showed no statistical difference in moisture retention between moldboard plowing, disc plowing, para-plowing, or chiseling.
d)--Best moisture retention is attained by keeping soils as cool as possible in the summer, and the air at the soil surface as calm as possible all year long.
SUMMARY: I feel there is value in this old research project (below) done in the 1970's. The four conclusions stated at the conference need to be altered in my opinion in light of the technology available to us today. All are still valid for a tilled field, but can be improved through a DS system; and, leaving long cut standing stubble following harvest.
More Detail:
Above is a study that was done in the late 1970's on soil moisture and what combination of tillage operations were best in conserving it in the fallow period. There are some interesting findings and conclusions. Direct Seeding was not on the radar when this study was done. The following are a dressed up set of my notes from an education event attended in the spring 1989. Below, I make conclusions/comments on this study as it may relate to Direct Seeding. Two separate studies were conducted with this research project.
1)-- Comparison of four primary tillage operations for holding moisture.
2)-- Determining the moisture use in a two year cropping cycle that included fallow.
#1 SUMMARY----The four primary practices were: A)--moldboard plow, B)--paraplow, C)-- Chisel, D)--Disc. The great disappointment at the end of this study was that there was no statistically significant difference in moisture retention between any of the operations.
#2 SUMMARY----The statements showing on the image insert are "from the time". Using DS, --- are these still valid statements?? What has intrigued me over the years, and is the reason for me hanging onto this information is the section: -- "where rainfall goes".
With todays bank of knowledge, the use of rotations in cropping, and using DS, I am confident that we can eliminate the 1% loss through deep penetration.
I'm certain that we can eliminate, or nearly eliminate 4% loss from runoff. (this summer our fallow took in the 6.5"event reported for that area without showing signs of runoff (no displaced residue or mudded over residue. In the bottom of the drainages there were the usual small cut channel; however, I couldn't tell whether they were from the winter/spring flush of snow, or from this event.) The conventional fallow around us was gutted to the depth of cultivation[4"-6"].)
This study shows we are raising our crops on 12% of the moisture received (through transpiration). Is this still a valid number? Just think of the potential!
This study shows that, of the rainfall we receive, 83% is lost through evaporation from the soil surface. Just think of the potential here if we reduce that number.
The numbers shown for seasonal variations,-- 1st winter @+66%, 1st summer @-20, and 2nd winter @ +41% are not to be construed as netting the 34% showing for the increase of fallow moisture over that of annual cropped ground. This image is poorly expressed. The study was on a winter wheat - fallow - winter wheat crop rotation. The correct interpretation of these numbers is:
The first winter following a winter wheat crop, the ground collects 66% of the moisture of it's two year cycle. Why?--The crop just harvested depleted the moisture in the soil profile so the hydraulic pull is strong and will accept all or most of the moisture that first winter, even with frozen ground. There was probably a primary tillage operation (moldboard plow, chisel, disc, paraplow) done to the ground prior to winter. Evaporation was probably the largest user. Some transpiration from weeds and volunteer. Some runoff is possible.
The "1st" summer [fallow period], the ground loses a net of 20% of the moisture collected over the two year cycle. (Why?-- Evaporation -- heat and wind movement across the soil surface are strong forces that hydraulically pull moisture up and off the soil surface. In our climate where most of our moisture comes in the winter, any and all summer moisture is over-ridden by evaporation. Also included is tillage where each pass across the ground stirs and aerates to the depth of 4-6 inches. This accelerates the loss by evaporation for that depth of soil. Traditionally there is little or no residue left on the soil surface, and certainly no residue left standing. This gives sun and wind high access to moisture through evaporation.)
The 2nd winter, that ground only gains an additional 41% instead of the 66% the first winter. (Why?-- The hydraulic pull is less the second winter because the soil profile has significant amount of moisture. The ground has been tilled a number of times since the previous crop, and the new crop has been seeded. The natural channels into the soil have been destroyed and most fields have the look of a garden with finely textured soil and no, or little residue remain. When that 2nd winter comes, moisture encounters a soil surface that quickly seals off allowing a high percentage of the moisture to flow across the soil surface to drainages varying with climatic conditions present. There is also a growing crop, and I don't remember how that complexity was explained.
The 2nd spring/summer, the soil profile is depleted of moisture. (Why?-- early on, evaporation is significant. Later in the season, as the crop grows and covers the ground, the evaporation forces decrease; however, the Transpiration force (growing crop) is very strong and will normally take the moisture down to the wilting point for the crop.
This study has influenced me for what has been done on this farm. In the 70-80's I recognized that tillage was destroying the long term productivity of our ground and began combining operations to reduce trips over the field. I also divided the slopes where there was crop on either top or bottom, and something else on the other. This shortened the run for water compared to the whole hill being one crop. From the 90's on, we have been in one form of notill/DS mode or another, trying to take advantage of what could possibly be attained from the above study.
Where are we today?:
Deep penetrating moisture: We haven't addressed this because of the low return on deep rooted crops like mustard and canola. That appears to be changing and those crops are looking more attractive.
Runoff: We have this element mostly controled. Including canola or mustard in our crop rotation will add a safety factor.
Transpiration: I don't know where we are on that one. I think the new commercial cultivars are more efficient in the use of, fertilizer and moisture. We are not fertilizing nearly to the level that the (currently used, but old) research states we need for the yields we are getting.
Evaporation: That, we are aggressively working on. The success, or not, will show in the future. My gauge for this will be when our 15"-17" rainfall zone can be annual cropped with results mirroring our current 18"-19" rainfall zone. We are addressing it two ways:
a) We have bought a Shelbourne stripper header. The first harvest (2012) is a raving success in wheat, barley and mustard. The winter wheat stubble (Brundage 96) is 38-40" tall with good density. This is the first barley stubble we have ever left that shows some capability to reduce air velocity on the soil surface. Instead of being about 4-6"tall, it is 22-24" and some areas taller. Since the barley and mustard ground will be fallow next year, we hope this will help decrease the evaporation. We have good surface residue cover on the barley. The mustard ground has less cover.
b)--We are building or refitting our DS drill with Cross-slot openers and associated technology. This is the ultimate low disturbance opener. We hope to have it ready for spring 2013. This fall (2012), we are renting that technology to seed the fall crop, but the frame designe significantly reduces the integrity of the technology built into the opener. The frame is designed for AB line operation on a flat, rectangular field.
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