Soil Salinity: How did farming cause it?
Hypotheses: Dead Roots? Road? Ditch? Toxin? Cation?
By: Grant Rigby February 22, 2016
Salinity can yield famine and starve civilization.
History: Our 1882 family homestead farm had no barren or white salt areas for over a century of grain farming until a few small patches of white surface salts appeared for the first time in 2000, nor had it for 10,000 years of variable Prairie climate following the pure water flushing of the ice age melt. After three decades of aggressive inputs, crops on the rich deep black soils around our sloughs, where crops had always been the tallest, were now stunted and worse than upslope, and an AgCanada soil specialist diagnosed both compaction and salinity as culpable.
Experience: With the objective of halting soil salinization, all herbicides and fertilizers, repetitive traffic compaction, and most fall tillage, were halted on our homestead farm in 2002. Clover, alfalfa and tall wheatgrass were sown in saline spots, and all wild perennial plants were allowed to live where domesticated species could not establish. Alfalfa timothy hay cropping in the fields, and now back to grains with sparse surviving alfalfa tolerated as well as adapted wild plants, but no barren fallow of course. No barren salt patches remain, foxtail has declined from swards to sparse, and crop stands are improving in fertile low areas where before 2002 they were declining. Research is necessary to conclude why, but we can surmise plausible truths.
The Scientists: Soil scientists, a full bus load tour, came to our old alfalfa-timothy hay field in SW Manitoba in August 2012. They investigated a 4 ft deep x 100 ft trench, dug from a tiny low patch where only the weed foxtail-barley could grow, up the adjacent eroded knoll, to view the salinity in the glacial till clay-loam chernozem soil.
The scientists analyzed the white specs present in the dry black top soil under that low foxtail-barley patch, to be the dry form of calcium-sulfate salt. Some wondered if the common practice of sulfate fertilization, in our nitrogen-phosphorus-sulfur blends for two decades until 2001, might have resulted in now common prevalent calcium-sulfate salinity.
The subsoil under that foxtail-barley patch was still wet, despite 12 months of drought and no water pond nearby. Its electro-conductivity, measuring total dissolved ions, was too high for any plant root to pull water away from the stronger osmotic hold of the dissolved calcium-sulfate brine. Adjacent quackgrass had failed to grow into the brine to displace the better adapted shallow-rooted foxtail-barley thriving above the brine.
Below this calcium-sulfate brine, at 3ft depth, was a vein of sand in the otherwise yellow clay soil of the trench. They surmised that sulfur and perhaps calcium had flowed with water to that point under the foxtail-barley patch, via the sand vein, from some higher origin under the knoll. When winds evaporated pure water from the hard barren field surface, in wheel tracks and in spring before protection via loose tillage or living canopy, the calcium-sulfate solution wicked to the surface via capillarity, and concentrated there in white salts as water evaporated.
The Questions: So what did we farmers do that caused sulfate and calcium to leave their origins in the subsoil of the knolls, to concentrate as their salt form in saline seeps? Why has salinity accelerated in recent decades?
Sod-breaking Hypothesis: Severing the deep living roots via ploughing, and thus ending the 10,000 year supply of photosynthesis energy to the deep living subsoil of the original perennial prairie, resulted in death of the deep subsoil ecology of plant roots, mycorhizae, bacteria, soil animals, etc, and release of its ancient biological sulfur as leachable sulfate. Biennial clover in the crop rotation, which had recaptured some sulfate, ended half a century ago, leaving just shallow-rooting annual crops that die at ripening. Only deep rooted wild rose endured tillage on knolls until modern glyphosate also killed it, releasing more ancient sulfate from the now half century continuously dead-fallowed subsoil.
If this hypothesis is valid, then imagine new agronomy to maintain some living deep roots to recycle biological sulfur within living soil organisms instead of leaching as sulfate, for example:
- Add clovers or winter rye at spring crop seeding, for deep living roots in fall to next spring.
- Maintain sparse alfalfa and wild rose plants within annual grain crop rotations, in precision strips, or via only shallow disking or selective herbicide, so deep alfalfa and rose endure within annual crops.
- Breed new biennial crops to replace annual crops, for example an edible sweet clover, sown and over-sown every spring for harvest 15 months later, to ensure living roots are always present in the subsoil.
Or, Soil Erosion Hypothesis: Tillage, water, and wind erosion redistributed the nutrient dense top soil within fields, yet the solar radiation remained uniformly distributed. Soil development, over 10,000 years, had left sulfur held within living organisms at the maximum concentration per unit of surface area that solar energy could sustain alive via photosynthesis. Carried by erosion, sulfur becomes surplus in low areas receiving eroded topsoil, due to limited solar radiation not sustaining an increase in total soil life to retain more sulfur within biology, so sulfate leaches.
If valid, then soil landscape restoration, removing soil accumulated at the base of slopes and applying it on the severely eroded hilltops, would not only restore soil health there (Lobb, 2015), but might also reduce salinity in the low areas by removing excess nutrients. Shredding woody brush to decay or burn on depleted eroded hills, would be preferred to the common practice of concentrating excess sulfur salts and risking salinity by burying woody brush piles in low areas.
Or, Roads, Ditches and Headlands Hypotheses: Look from most roads, and it is clear that the road's existence has promoted salinity in adjacent fields.
Burying ancient topsoil within early road construction killed it, likely releasing its sulphate ions.
The deep living cloak of ancient deep prairie biology had also stabilized clay colloids holding adsorbed calcium and magnesium ions, and upon biology's death the ions became more mobile and moved by capillarity upwards to the road surface, to be wind blown or rain washed into ditches and fields. Ions below biology's original depth were also exposed and freed via cutting road and field drainage ditches.
Roads built of expanding clay swell like a sponge with distilled water from rain and snow, and then release ion-enriched solutions when compressed under each truck or train, drawing in the ditch water and then pumping it downwards and laterally via pressure wave through the spreading compaction under adjacent fields. Whereas pipelines recovered with vegetation and free of pulsating weight load, appear to not cause salinity.
The calcium-sulphate solution climbs upwards in fields by capillarity first wherever implement compaction has closed air pores and annual cropping has eliminated deep root soil drying perennials. Washboard vibration also settles soil in air pores, limiting aerobic root depth in adjacent fields.
Salinity first occurs within fields where implement weights are raised onto wheels and where the equal opposite forces for changing immense tractor momentums turning on headlands, for acceleration, and for shovels ripping soil upwards, are pushed downwards and laterally under the wheels, where tramlines are deliberately repeat compacted by heavy sprayers, where grain trucks punch down soil on headlands and approaches, and where old trails are compacted in pastures as evidenced by only foxtail-barley surviving.
Toxins such as benzene from asphalt, persistent lead from gasoline and cadmium from tires would also diminish soil life in adjacent fields. Greater tractor tire wear turning at headlands and field corners adds greater fungicidal cadmium there. Cadmium in phosphate fertilizers concentrates at headland overlaps.
If all valid, then salinity would be delayed by choosing the lightest tractors and implements, by replacing tractors with self-powered implements of even weight distribution on closely spaced wheels, by avoiding turning implements where salinity is risky adjacent to roads and sloughs, by reverting to round and round operations, by avoiding driving twice on the same trail, and possibly by replacing tires with steel tracks. Correlations between field salinity and road history, clay type, paving material, open shoulders, mowing, ditch vegetation, drainage, etc, would guide road design improvement. Roads of expanding clay might be covered to remain dry, and rebuilt of non-expanding mineral where ditches cannot drain, or restrict road usage to when dry or frozen. Weeping tile could be installed below ditch bottoms. Trains could be replaced with uniformly loaded conveyors for bulk or boxed products. Growing biomass energy in ditches and hay on headlands adjacent to roads could better capture opportunity by harvesting surplus sulfate and calcium ions. Establishing perennials in cut field drainage ditches would stabilize exposed subsoil and retain ions in the subsoil instead of release into waterways onto other farms.
Or, Sulfate Fertilizer Hypothesis: Sulfate anions (negatively charged ions) from ammonium-sulfate fertilizer, never fully utilized by crops, become leachable excess sulfate.
Ammonium-sulfate also reacts with the white calcium-carbonate in eroded knolls, yielding calcium-sulfate (Prasad + Power, Soil Fertility for Sustainable Agriculture, 1997).
If valid, then elemental sulfur might be preferred, as it requires active conversion by bacteria to leachable sulfate, which is more likely to occur where sulfate is deficient in the soil ecology.
Or, Ammonia Fertilizer Hypothesis: Ammonium cations (positively charged ions) from fertilizers displace calcium cations from the cation exchange surface of negatively-charged soil clay colloids (from Brady, The Nature and Properties of Soils, 1974). Once calcium is displaced and washed downwards with rain, it can never return to the dominant intricate arrangement within clay lattices it occupied for 10,000 years. Plants then replace the ammonium on the clay with hydrogen, so that spot is occupied preventing calcium's return. Soils depleted of calcium become aged soils, with altered physical properties, such as poor plasticity thus mucky when wet. The displaced calcium cations join the sulfate anions in solution, ultimately accumulating in deep gravel or lakes, or concentrating in surface puddles of calcium-sulfate salinity. Displacement from clay also occurs for magnesium to form magnesium-sulfate salinity. When wet soils are bare, such as fall-harrowed or tilled lands come early spring, water evaporation draws up water by capillarity, picking up the displaced calcium to concentrate it on the surface. Salinity would thus first appear where cationic fertilizer applications overlapped at headlands and over-dosed in field corners, as more free calcium has been displaced there by more added ammonium ions.
If valid, then dilute urea solutions or slow release urea, well mixed into the soil, instead of banded ammonia, might delay salinity occurrence. Or grow own nitrogen via companion cropped legumes every year, or add a legume green manure year, to fix nitrogen wherever deficient. Or, stabilize ionic fertilizers onto locally mined clay before addition to farmland, a plausible process to enable fertilization of low cation-exchange-capacity soils in Africa.
Or, Herbicide Residues Hypothesis: Some bio-degradable herbicides may concentrate and remain un-degraded in saline seeps due to high salts inhibiting microbial life, adding to difficulty establishing crops. Pesticide registrations likely do not test for biodegradation amongst saline salts, yet pesticides are typically applied to saline soils, possibly illegally.
If valid, then avoid pesticide use in saline areas.
Or, Glyphosate Hypothesis: Chelating of metal nutrients such as zinc, copper, iron, manganese by systemic glyphosate, (originally patented as a metal chelator), within the growing tip of a deep alfalfa or thistle root, and distant from topsoil bacteria which may have adapted to degrade glyphosate, may result in the perpetual unavailability of those essential metal nutrients at that location. That inhibits living decay there by fungi, its recycling of nutrients, and re-rooting of future crops in that poisoned spot. Upon tie-up of the trace metals essential in synthesizing the enzymes of life, other nutrients which had for 10,000 years been assembled by biology in nutritional balance at that location become surplus. Surplus sulfate would be released, and soil adhesiveness, air porosity and depth of accessible water be diminished due to absence of soil life.
If valid, then for canola, non-systemic glufosinate-ammonia tolerance would be preferred over systemic glyphosate tolerance. For quackgrass control, other grass herbicides such as sethoxydim, or chisel tillage of patches, would be preferred. Abrasive particles spray can be developed for pre-seeding, and optical row guidance tillage for narrow row weeding.
Or, Fungicides Hypothesis: Plant decay is a living process conducted by fungi to intimately transfer residual energy and component nutrients for reuse within a new organism. Fungicides prevent this transfer of nutrients into living fungi by killing fungi. Nutrients can be lost from reuse within the living ecology when fungicides cause dead disintegration instead of living decay. Phosphate and sulfate are then extracted like tea from sterile dead leaves, onto a fungicide-inhibited soil surface, to run-off or leach into saline seeps and lakes. Systemic fungicides may poison wheat roots' symbiotic fungal mycorhizae, weakening soil cohesion and releasing sulfate as the mycorhizae disintegrate.
If valid, then short-lived contact fungicides would be preferred to systemic fungicides.
Or, Distillers Dry Grains Hypothesis: Well water is added to corn to enable yeast to convert sugars into alcohol. Alcohol is first distilled, and then pure water boiled off. All salts from the well become concentrated in the DDG livestock feed, and thus in fields wherever the manure goes.
If valid, then distillers might internally recycle their water, to keep salts out of DDG.
Or, Slough Rings Hypothesis: Water held in sloughs/ponds wets laterally and about six feet upwards via capillarity into adjacent fields. Within the first few feet of the edge of sloughs, the typical good crop growth there suggests it gets annually flushed of any excess calcium-sulfate field salts via dissolving into the distilled snow melt water as it climbs up from the slough to the ring in the field where salts accumulate. (If sulfate had originated in slough water, there would instead be greater concentration of salts closer to the slough edge, not in the upslope ring, due to slough water continuing to wet only lower levels of the surrounding field as its level dries down over summer.) From the hill above, waters also carrying displaced calcium-sulfate would leach down slope through the subsoil until colliding at the slough water wetted boundary ring, concentrating its upland sulfate there at the ring as its pure water evaporates. A greater ring salt concentration correlating with a longer hill above the ring, would suggest those salts originated due to farming practices.
If valid, then planting hay as a salinity barrier in low areas will be ineffective in halting the excess calcium-sulfate originated in upland subsoil and slowly leaching for many years, but would reduce evaporation concentrating those salts at the surface because deep perennial roots continually draw water from depth allowing rainfall to permeate downwards.
The typical good crop growth adjacent to old slough edges might also owe to the 10,000 year old continuous subsoil life of its ancient deep sod. Ancient mycorhizae receiving energy from the perennial plants might extend under the field, symbiotically supporting our crop plants with nutrients and stimulants. Ancient porosity facilitating deep oxygen for roots might also endure.
If valid, then re-establish deep-rooted perennials such as sparse wild rose or alfalfa within our annual crops, perhaps one enduring plant every six feet, to retain nutrient life on hills.
Or, Over-Grazing Hypothesis: Daily leaf removal via grazing of pastures near to gates and barnyards reduces the daily photosynthesis energy available to fuel root life by using it instead for cattle, starving deep roots, leaving only shallow roots. The deep subsoil biology no longer receives energy from root exudates and dies, releasing its ancient sulfate.
If valid, then rotational grazing, or retaining some unpalatable, thorny or alternate use perennials in pastures to discourage daily grazing of all deep-rooted perennial species, such as endured in productive old Australian pastures (from Entz), would be preferred.
Or, Cattails and Algae Hypothesis: Depletion of nutrients from the subsoil of uplands, plus surplus fertilizer applications, may have nourished the expansion of tall lush dark green cattail displacing the original grasses in sloughs. Toxic blue-green N-fixing cyanobacteria might flourish in lakes due to receiving an influx of prior-limiting P, S, or Fe essential for its nitrogenase enzyme, due to salinity processes in annual cropped farmlands.
If valid, then harvesting cattails or pond water and adding to eroded knolls would re-establish nutrient uniformity, plus return the ecology of marshes back to favouring finer species for hay. Halting salinity processes would ultimately improve Lake Winnipeg.
Or, Salinity as Fertilizer Hypothesis: Colour variation in saline areas could identify various different nutrient concentrations. Where not a white salt, sulfur might be depleted.
If valid, then first simply harvest the visible white calcium-sulfate salts whenever dry on the surface, and spread back onto eroded knolls to re-establish nutrient uniformity. Old farmers with grain shovelling skill might thus earn redemption. Or use a light ATV to scrape up dry nutrients while avoiding wet subsoil compaction.
Flooding Hypothesis: Soils temporarily flooded, such as the bottoms of drains, typically grow taller plants than adjacent saline soils, due to salts dissolving then flowing off.
If valid, then back-flood saline flats to dissolve sulfate, for big gun or trickle irrigation onto knolls, or flush into a lined catchment, evaporate to concentrate and sell as sulfate fertilizer.
Drainage Hypothesis: Tile-draining fields, and draining sloughs into lakes, remove excess calcium-sulfate in low areas, but if the above hypotheses are valid, do not correct the agronomy errors that cause the continuous bleeding of scarce nutrients from the upland subsoil, limiting future rooting depth and diminishing sustainable food potential there.
Saline Forage Suggestion: After skimming off the visible salts, perhaps sow low-coumarin sweet clover, alfalfa, timothy, volunteer kochia, dandelion and quackgrass for hay or into silage to soften foxtail-barley awns. Wherever plants can't grow, immediately cover with straw or fabric, or till a loose soil mulch, to halt evaporation from barren hard soil and the salt concentration it drives.
Actions: Salinity ratings can be required for fertilizer and pesticide licensing. Compaction ratings can be required for turning and operating new farm implements.
Students of science can critique and imagine experiments to test hypotheses. Governments can fund independent research. Individual farmers, and their commodity associations, can correlate management histories with differing salinity on adjacent farms, discern lessons reading the landscape, and openly discuss, to advance agronomy wisdom to halt salinity.
By: Grant A. Rigby, B.Sc.Agronomy, M.Sc.Food, copyright, independently written.
Passion, photo: www.agannex.com/field-crops/where-did-the-salinity-come-from
First published: Manitoba Cooperator Nov 27, 2014. Updates: www.rigbyorchards.com