Managing Soil Health

As managers using soils for production, what do we look at, what do we (want to) see? After decades of regular use of single-super phosphate some farmers and graziers stopped using it when they became aware of the detrimental impact it had on soils and trees, caused by the acidic nature of the fertiliser; use of muriate of potash (potassium chloride) has similar impact and also needs to be avoided.

We can learn to use the power of nature rather than fighting it with synthetic chemicals and unproven new technologies in a war we can’t win. Organic Farming is surging and Biological Agriculture (Anderson 2000, Zimmer 2006) is emerging as a sophisticated farming system in transition between current and organic. Both benefit from reintroduction and enhancement of humic and soil biological activity, components already fundamental in Biodynamic Farming (ATTRA 2006).

In contrast to the Organic standard, Biological farming allows for minimal use of the most microbe-friendly fertilisers and herbicides with humic additives and molasses or sugar to enhance effectiveness and reduce damage to microbes. This requires ever smaller quantities as the system is balancing and moving towards Organic, a process that occurs much more quickly when actively managed with biological inputs.

Management aims to balance chemistry, physics and biology in the soil aided by improved organic carbon content, appropriate mineral balance and a diverse and abundant soil life. Thus stabilising our fragile soils and creating a sponge that stores and makes available required plant foods and facilitates prolific root growth. Soil biology helps with building and maintaining soil structure to secure aeration and prevent compaction. A balanced biological soil will have the maximum levels of available minerals coinciding with maximum demand by plants.

The farming system is intended to enhance biological activity in soil and on foliage, enabling a balanced supply of required minerals for effective plant growth, providing energy to plants and grazing animals. Soils are actively re-mineralised, inoculated with soil microbes and supplied with food for microbes, all required in order to achieve and maintain an energetic balance.

Cover – With cropping and in orchards, the soil should be covered most of the time by green plants or at least stubble to protect from high temperature and water loss. A litter layer as cover will be a continuous source of carbon for soil organisms and also provide temperature insulation and water retention. Green manuring provides opportunities to convert rainfall into soil fertility.

Weeds – Weed growth is minimised with soil minerals being in balance and with lowest levels of freely available nitrogen. Mineral availability provides conditions that produce certain weeds, which can be used as an indicator of mineral deficiencies (Walters 1999). The weed spectrum changes immediately when soils are balanced using appropriate materials. For example, from stinging nettle domination (sign of calcium unavailability) one year to no nettles and some shepherd’s purse as the main weed the next. This is the ecological concept of succession, with different suites of species supported on the same area of land as soil conditions change over time (see e.g. Ingham 2006).

Insects and diseases – Biological farming is non-pesticidal management (NPM) and uses natural techniques to prevent insect and disease damage. This is a major step ahead of integrated pest management (IPM) which aims to minimise pesticide use to prevent or delay resistance. Preventative measures are important before and after sowing but start with a healthy soil where biological activity builds internal plant resistance to diseases and insects (Callaghan 1975, Anderson 2000, Ingham 2006). Depending on the risks and size of operation, the management options are crop sequence, inter-cropping, trap crops/weeds, seed and foliage inoculation, neem and other natural repellents.  Plant sap sugar content can be used as a guideline for protective sprays (see ‘Tools’ below).

Variety choice – Most current varieties have been selected to produce well in high-input management systems and require such treatment to perform as expected. New varieties need to be developed under organic-biological conditions to optimise production with low input on healthy soils. The first step is to evaluate ‘old’ varieties that were selected before nitrogen availability became a priority for plants.  A variety will improve with successive seasons if the seed is retained and used again as it keeps adjusting to local soil biology.  

– The rhizosphere is the area of intense biological and chemical activity close to the root inhabited by soil microbes feeding off exudates from the root, thus facilitating nutrient supply to the root and protecting it from pathogens. Fertiliser applied with the seed at sowing decreases root growth, root branching and the number of root hairs. Applying microbes, humic substances and food for microbes with the seed (ie inoculation) generally results in a vigorous seedling with many roots, a thick rhizosphere, prolific branching and many root hairs, without the need for conventional seed-dressing. Such annual plants when pulled out of the ground at flowering still show a vigorous rhizosphere. Microbes keep colonising the roots as they grow, thus providing a continuation of that good rhizosphere. It has been demonstrated that an active rhizosphere can be created in degraded, acid or saline soils, with that neutral zone around the root allowing vigorous plant growth. Such a ‘carbon pump’ into the soil will improve that soil and the increasingly active soil biology will segregate negative compounds. Carbon may thus help stop dryland salinity (Jones 2006).

Inputs – The most important inputs are foods for the soil microbes, with the most effective one being carbon exudates from roots of growing plants. Maximising the time of active plant growth is therefore most important. Rotational, cell, or planned grazing (large number, small area, short time), for example, facilitates root growth and delivers more carbon to the soil than set-stock grazing. Another example is pasture-cropping where winter crops are sown into summer-active perennial pasture (Bruce 2005, Jones 2006, Seis 2006).

Residual stubble and roots are also important sources of carbon. Stubble, however, needs to be broken down to be available for soil organisms. To facilitate this if breakdown is slow, a stubble digest, containing cellulose-digesting fungi and some urea to lower the C:N ratio, can be sprayed onto slashed, spread and rolled stubble with or without incorporation. Such management decisions depend on the amount and kind of stubble, paddock history and soil biological activity – i.e. whether or not such bugs are already present.

Carbon can be applied as molasses, sugar, humates or brown coal (in order of decreasing availability). Humic substances, such as humus, humate, humic acid, fulvic acid and humin, are important forms of carbon for plants, playing a vital role in soil fertility and plant nutrition. Plants grown on soils which contain adequate humin, humic acid and fulvic acid are healthier and less subject to stress, and the nutritional quality of harvested foods and feeds are said to be superior (Pettit 2006).

Soil microbes, food for microbes and minerals can be applied as required by spreading, down the tube, or as foliar or soil spray with possible micronised minerals. To provide an optimum start of plant growth through the creation of a vigorous rhizosphere, the standard practice is to inoculate seed with microbes. This can be done by tickling some 10 l/ha of microbe containing liquid on the seed at transfer from silo (needing less then 20 minutes to dry before sowing), or dripping a liquid containing microbes and minerals in the soil on the seed while sowing.

Microbes can be applied as compost tea (Ingham 2006) or as a commercial mix (e.g. the internationally well known ‘EM’ (Effective Microbes) or ‘4/20’). These mixes may contain free-living nitrogen fixers (e.g. Azotobacter), bacteria that establish in the litter layer and can provide 20 to 70 kg N per ha per year depending on moisture and carbon availability. Phosphorus solubilisers are another bacterial group that may be included to make available the P applied in the past and locked up in soil clays. The importance of Biodynamic preparations (e.g. 500, 501, Cow Pat Pit) and application (time and method) does not just rely on bacterial content, but also on their stimulation of the activity of other soil bacteria and fungi.

Other inputs can be organic in nature, such as seaweed, fish protein, guano, soft rock phosphate, lime and rock dust, or in biological farming, inorganic microbe-friendly fertilisers in small amounts, such as sulphate of ammonia, calcium nitrate or mono-ammonium phosphate (MAP). Lime is regularly applied (0.4 to 1 t per ha) for calcium to be available – a very important mineral requiring fungi for availability to roots (e.g. Ingham 2006). Compost is an important and effective method for delivering carbon, organic compounds, minerals and microbes to the field as a readily available organic fertiliser. The best compost contains up to 90% of the carbon in microbial biomass, that is, bacteria, fungi, protozoa and nematodes (Ingham 2006).

Compost tea can be extracted from good compost and sprayed in orchards and on broadacre crops and pasture. Vermicomposting is the process by which worms are used to convert organic materials into a highly effective humus-like material known as ‘vermicast’ and its effluent ‘vermiculture’.

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