Creating and Sustaining Soil Health

Transcription

1 Creating and Sustaining Soil Health Jill Clapperton Ph.D. Principal Scientist Rhizoterra Inc Copyright Rhizoterra Inc We help you make decisions based on science

2 So why do we treat soil like dirt? Copyright Rhizoterra Inc

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4 Biological Chemical Soil Health Physical Food quality Soil productivity Environmental quality Health

5 What characterises a healthy soil? The soil is alive, well and the plants are thriving Good soil structure Large number of functioning soil services Limited soil erosion Increased nutrient cycling Nutrient availability and recycling Water holding capacity, filtering Biodegrading toxic compounds Diversity of soil organisms Healthy nutrient dense plants

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7 The key factors that influence soil health- this woman s opinion Reduce or Eliminate Soil habitat disturbance the first principal of conservation agriculture Increase soil organic carbon The second principal- keep the soil covered Increase the diversity of soil carbon compounds by adding plant root diversity The third principal- rotation Add perennial crops into the rotation, which means integrated livestock grazing

8 A healthy wheat crop on soil that is regenerating

9 Peas vetch and oats good the ground.

10 Good for Livestock and Profits

11 Oxidized SOM from roots that have penetrated deep into the soil profile. Create channels that move water, air, mineral nutrients, and more to the roots Earthworms are the chief soil engineers. Copyright Rhizoterra Inc

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13 Soil organic C: feeding the soil to feed the plants Increasing water holding capacity Copyright Rhizoterra Inc

14 Historically speaking In June 1944, ES Hopkins and A Leahey scientists from the Experimental Farms Service, The Dominion of Canada Department of Agriculture published Farmers Bulletin No. 124 on Crop Rotations in the Prairie Provinces. They presented research findings, beginning in 1901, on the effects of commercial fertilizer, farm manure and green manure and concluded that:

15 Mixed farming rotations had an outstanding advantage over the grain rotations. The three-year grain rotation C (summerfallow-wheat-wheat) has become polluted with wild oats which has very seriously reduced the yields while in both the mixed-farming rotations the land is practically free of the weed. FYI- Wild oats are a great indicator of available inorganic nitrogen Organic nitrogen loss after 22 years of cultivation was 30% (10% from grain and 20% from plowing) on the prairies (Indian Head Experimental Station, Saskatchewan Canada). The good news was that after another 16 years (38 years of plowing), the total loss of organic N was only 40% (17% from crop and 23% from plowing). They concluded that losses from plowing decrease with time (and of course so did the total organic N, C, P, and S as the soil organic matter was burned up).

16 Getting to the root of soil health

17 Yellow sweet clover Phacelia Arrowleaf clover Diakon Radish

18 Faba Bean Persian Clover Sunn Hemp Wooly Pod Vetch

19 Soil Food Webs Soil food webs are mainly based on three primary carbon (C) sources: root exudates, litter or residues, and soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, and can thus, increase the C flow and biodiversity within the food web.

20 Soil Food Webs Soil Carbon from roots is retained and forms more stable soil aggregates than shoot derived C (Gale et al. 2000) Roots normally account form only 10-20% of the total plant weight Contribute 12% of soil organic C, 31% soluble organic C, and 52% of the microbial biomass C (Liang et al. 2002)

21 Soil Food Webs The amount of carbon from corn roots and corn root exudates can be as much at times higher than the organic C contribution from corn stover (Allmaras et al. 2004; Wilts et al. 2004)

22 Photosynthesis (perhaps overly simplified) Plants converts CO 2 from the atmosphere to simple sugars (photosynthate). These sugars are moved around within the plant and used to make amino acids, organic acids, lipids and other carbon based molecules. Plants export sugars to the roots so they don t build up in the leaves and halt photosynthesis. We get sun and rain for free lets catch every ray and every drop.

23 Symbiosis Growth promoting substances Rhizodeposition Nutrients Water Growth inhibiting substances

24 Root Exudates and the Rhizosphere European Encyclopedia of Soil Biodiversity

25 Increasing the amount of carbon exuded from the roots drove the microbes to release more extracellular enzymes to breakdown the organic N accelerating the turn over of organic N in the soil- a cascading (Phillips et al. 2011, Ecol. Lett. 14: ).

26 Rhizosphere Plants Plants chemical Organisms chemical Soil Organisms physical Soil physical

27 The quality and quantity of root exudates determines the function and population density of the microbial community associated with the roots

28 Amoebae can engulf bacteria in the tiniest soil pore, fungal spores and protozoa. There can be as many as 40,000 in a gram of healthy soil. European Encyclopedia of Soil Biodiversity

29 The percentage of N in the roots as nitrate (blue), amino acids (green), amides (yellow) and ureides (red). These compounds leak from the roots as exudates and are part of the plant s signature to create a unique rhizosphere.

30 Soil Organic Matter (SOM) SOM is the primary food source for most soil organisms The quantity and quality of SOM is what drives nutrient cycling C:N between 30 and 50:1 is ideal for optimised N cycling.

31 Aboveground diversity is a mirror for belowground diversity, and carbon from photosynthesis is fueling the system.

32 Weeds vs Natives Cheat grass or Downy Brome (Bromus tectorum), Japanese Brome (Bromus japonicus), and dandelion (Taraxacum officinale) all produce root exudates that inhibit bacterial nitrification (stop the conversion of NH 4 to NO 3 ). Native grasses such as Stipa comata (Needle and thread grass) have exudates that promote nitrification. John Neal, Can J Bot. 1976

33 Plants colonised by mycorrhizal fungi have higher rates of photosynthesis and export more amino acids, organic acids and neutral sugars to the roots compared with non mycorrhizal plants (Clapperton and Reid, 1992).

34 Rhizosphere interactions and processes Beneficial Symbiosis Growth promotion Soil stability Water uptake Nutrient availability Nutrient uptake Enzyme release Biocontrol Antibiosis Competition Allelopathy Deleterious Growth inhibition Infection Phytoxicity

35 Plants, Soil and Soil Organisms Each plant species or crop species modifies the soil and soil organisms in ways that can benefit, inhibit or have no affect on the establishment and growth of the subsequent crop. We can use these processes to manage crops, weeds, diseases to increase soil and plant health and productivity, and animal and human wellness. The Rhizosphere Effect

36 Further study is required to realize the potential for targeted cropimprovement strategies based on root traits that favor carbon sequestration in soil while also efficiently producing food. Richard D Bardgett (2011), The Scientist, August 1, 2011.

37 Genetics Matter Balancing yields and root growth. DSV wheat breeding trials in Assendorf, Germany. Which variety would you choose?

38 In a model grassland system it was recently shown that increasing plant diversity enhances CO 2 assimilation by surrounding plants. This in turn increased the amount of C allocated to the roots and mycorrhizal fungi, which is a key mechanism driving carbon sequestration in soil. These effects, however, were due to the presence of legumes in high-diversity mixtures, rather than to diversity per se (Gerlinde De Deyn et al. 2009, Journal of Ecology 97: ).

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