Soil Moisture

[Update: Jan 5/15] --- Web search shows several studies, ( Canada, Nebraska, Colorado, Washington) where the 13-14m fallow period in a wheat-fallow rotation store a low of <20% to as high as 34% of the moisture received.  The more I discover the more I'm becoming convinced that fallow is a loser.  Even cropping environments with 6" annual rainfall would be better off developing a crop rotation that includes building biomass and growing tall residue with annual cropping.  The other 66-80% of the precipitation received is lost, primarily through evaporation.
[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.

Shelbourne Header -- 1st harvest - 2012

[Click on the label "stripper head" at the bottom of post for more posts on the subject.] 

 SUMMARY:  We harvested Brundage 96 winter wheat, Bob spring barley, and IdaGold spring mustard.  We are pleased with the results on all three crop types.  With the mustard, all of the tops are taken off and run through the combine leaving a ragged looking field with stems of varying lengths.  Wheat stubble looks daunting with 38-40" remaining standing.  Barley stubble stands 22-30".
MORE DETAIL:
        Winter Wheat:  Header was relatively easy to control even with an inexperienced operator.  It will take some time to gain experience to gage hood height and rotor speed for optimum performance.  Header loss was very low, but without straw in the machine, distribution across the sieve dramatically changed.  Our losses are higher than I find acceptable.  After about 50 hours, Kye has concluded that most of what is going through the concave is dropping onto the right side of the sieve, which is an overload.  Before next year we will have to make changes in the distribution augers or the floors of the augers to move material further across the sieve.  We'll need to have some adjustment capability because improvement will be through trial and error.  AND-- we will have to convert back to use this machine with a standard header for some crops (canola as an example).
         Spring Barley:  Barley harvests much more efficiently than with a standard head. Less head loss, less green in the tank including unripe kernels.  This is a great (and pleasant) surprise!  Barley has never given me much self satisfaction regardless of yield, because of the associated head loss.  Barley is inherently weak strawed which lends itself to lodging, and heads, if of good quality, tip over at the neck giving opportunity for catching on the reel.  Between the reel tossing heads,  and leaving the low heads on the ground, it is frustrating.  This header is going to save 100+ pounds of barley per acre.  We found that you cut patches that cut off from the main field immediately.  The edge of the cut and un-cut is difficult to distinguish, even at a short distance.  With barley, you break off the head stem at the crook, and the top portion of the stem is left frayed, giving a similar appearance to that of beards.
           Minimizing moisture loss with barley stubble for the following chemical fallow period is challenging.  Soil moisture loss is a given for the fallow period.  Fallow only provides approximately 30% more moisture to the following crop than annual cropping provides (see another Post -- labeled, moisture.  Barley is normally cut at, or near ground level offering little or no wind protection at the soil surface.  Convection pulls moisture to the surface developing a layer with higher humidity.  There is a point where that layer of higher humidity will slow convection.  Air circulating at the soil surface removes this layer.  The higher the wind velocity across the soil surface, the stronger the pull on available moisture.  This header leaves a much better condition.  The canopy (shading) is reduced when the head is removed; however, the height is not reduced.  Heat will still have a drying effect; however, the higher stubble reduces the wind velocity across the soil surface reducing the degrading of the humid layer.

Shelbourne Stripper Header

[Click on the label "stripper head" at the bottom of post for more posts on the subject.] 

Summary: We are very happy with the decision to purchase the header.  This old high capacity machine has a new life with more capacity, and the principal problem of poor residue distribution is eliminated.  Header loss was low in all three of our crop types (winter wheat, spring barley and spring mustard).  

2012 harvest

More Detail:
This pic shows a 2012 CVS32 mounted on our 1985 Gleaner N7.  This was a calculated $70k gamble.  Improving yields over the years along with the poor residue distribution associated with the N7, were adding to problems associated with our Direct Seeding.  We love this machine with it's low profile, wide stance, large bulk tank, high capacity, ease and low cost of repair, great horsepower to weight ratio, and the ability to harvest and save the grain on our slopes that max out around 40%.  I'll give more detail on the N7 and changes to accommodate this 7000#, 32 foot header in a later post.  My emotions have run the gamut, from excitement when Kye ordered it, to apprehension as I read more "tractor house" forums and Utube videos, to being ecstatic after only a few days of cutting.  It handles very easy, our capacity is up, our ground speed is slower at this point in time,  and I'm sure we will hit 10kbu/d before the old girl hits her 28th birthday -- although it will be a longer day and our two man operation will become three.  One truck driver can't haul that much grain away from this machine in our operation.

This pic shows stripping Brundage 96 winter wheat in a small ravine at sun down.  Very quiet air.  Notice the thin layer of dust at the header.  Since the header is basically a sealed unit using either metal or a crop wall, there is much less dust generated in that area compared to a standard wheat header.   The dirt plume out the back is dense and lingering.

This pic shows the interaction between header and grain.  As you drive through the standing grain it is pushed forward, bent down along curved nose where the rotor engages the wheat and combs through the straw, drawing it up behind the nose into the curved portion on the back side of the adjustable hood, where the kernels are pulled off the center stem portion of the wheat stalk and propelled back into a deep auger trough, where it is transported to the feeder house. This rotor rotates between 400 and 800rpm.  Approximately 85% of the threshing is done by this rotor, leaving only 15% to be threshed by the combine rotor.  The un-threshed tend to be the tips of the wheat head.   We have harvested some lodged wheat and it did fine as advertised; although more material is put into the combine.

This pic shows the transition between harvested and unharvested wheat.  The preferred rotor speed is where the center stem portion of the wheat head is not flailed off, but left mostly intact.  This leaves the appearance that the stubble at times seems taller than the wheat crop itself.  Our stubble in 2012 is 38-40" tall.  

This pic shows the machine entering the cut on a ≈30% slope.  The camera does not  give it justice.  We added a header tilt package to the machine which is helpful harvesting steep slopes, and dips that you angle through.  Another change that proved out, was to replace our 18" outer duel wheel.  We now have two 24.5x32 wheels/tires.  We only added 2" extra width but the stability with more rubber on the ground is noticeable.  It climbs and stays on the hill better.  Where we don't level the machine, a lot of weight is transferred to the lower side.

This pic shows stripping spring barley.  It's the 1st time we have ever cut barley with more than about 6" left standing.  About 30 inch stubble is showing here.  

This pic shows stripping mustard.  Header loss appears comparable to a standard header.  Noisier than harvesting wheat or barley.  Seed hitting the curved metal surface of the hood is distinct.   The residue remaining is fairly tall and ragged.  Most of the top portion of the plant was stripped and run through the machine, leaving a noticeable row of tangled material inside the wheel width.  I don't think the volume of tangle will be a problem to seed.  It is mostly intact and pretty thin. We have no chopper in this machine.   This will be fallow.  We'll compare end result with barley residue for the fall 2013 crop. Our experience in 2002-2003 was that we received a significant yield boost in the wheat following mustard.