SOIL HEALTH CONCEPT

Soil testing and fertilizer recommendation basically involves need based fertilizer use with little thrust on the microbial diversity a crucial factor in maintenance of soil health. A reorientation of soil test advisories including soil health/quality parameters is of top most significance. Knowledge of soil health parameters that promote sustainable productivity growth with zero land degradation have to be identified. An understanding of the soil health concept involving physical, chemical and biological properties is therefore important from the point of view of identifying appropriate diagnostic tests that aid development of soil health management strategies.
Soil health/quality refers to the physical, chemical and biological features of a soil that are essential for long term sustainable agricultural production with minimal environmental impact. Although, it cannot be measured directly, soil health can be inferred by measuring specific properties like pH, electrical conductivity, organic matter content, cation exchange capacity, base saturation and by estimating soil status of plant nutrient elements (fertility) and microbial activity as well as microbial diversity.
Healthy soils occur when their biological, chemical, and physical conditions are all optimal, enabling high yields of crops. When this occurs, roots are able to proliferate easily, plentiful water enters and is stored in the soil, the plant has a sufficient nutrient supply, there are no harmful chemicals in the soil, and beneficial organisms are very active and able to keep potentially harmful ones in check as well as stimulate plant growth. Essential functions and services generally expected from healthy soils are given in figure

SOIL BIOTA

Life in the Soil

Soil food web

The soil microbes include a wide range of organisms viz: microflora represented by (bacteria, fungi, algae and actinomycetes), microfauna (nematodes, protozoa) and mesofauna (collembola, mites).all these organisms together are involved in a multitude of functions like decomposition of organic matter (crop residue), mineralization and recycling of nutrients, fixation of nitrogen, detoxification of pollutants, maintenance of soil structure, biological suppression plant pests, parasitism and damage to plants. They also aids in maintenance of soil resource quality and environmental health in both natural and managed agricultural soils. A diverse balanced and active soil biota could help provide soil conditions necessary for sustainable crop production with little negative environmental effect.

Enhancing microbial activity and soil health

Maintenance of soil health demands a long-term commitment using various combinations of soil management practices that enhance microbial activity. The following strategies will help in sustaining soil health and production of healthy and quality crops

• Add sufficient quantities of organic matter from cover crops and other crop residues as well as from off-field sources like animal manures and composts. Organic materials from various sources have different effects on a soil’s biological, physical and chemical properties and have modifying influence on pest and disease incidence
• Mulching with living vegetation or crop residues protects soils from moisture loss, extremes in soil temperature and allows maintaining population of soil micro and macro organisms including earthworms
• Minimum or zero tillage leaves more crop residues on the soil surface which creates a stable environment, slow turnover of nutrients and encourage more diverse communities of decomposers
• Minimize soil erosion through appropriate management practices to retain top soil rich in organic matter which is crucial for maintaining soil health
• Soil acidity amelioration through liming is necessary to maintain soil pH at optimum levels to enhance nutrient availability, reduce toxicity and prevent soil borne diseases
• Adopt the best management practices to supply nutrients to plants based on specific pathogen/nutrient interaction. Routine use of soil and plant tissue tests will help to regulate nutrient supply based on soil/crop needs and provide a balanced dose. Vegetative resource management by limiting external inputs, and use of indigenous organic matter supply and nutrient recycling will help to improve microbial diversity
• Replace agrochemicals with more resource-efficient, environmentally safe practices for managing nutrients and reducing pest and disease incidence

NUTRIENT MANAGEMENT

In organic farming, soil physical, chemical and biological properties are maintained primarily based on the use of onfarm organic inputs like farmyard manure, compost, oilcakes, biogas slurry crop residues, green leaf manures and in situ green manuring. Besides, approved mineral bearing rocks, biofertilisers and Vrikshayurveda products can also be used for improving soil health and maintaining productivity.

ROCK DUST AND REMINERALISATION

Application of rock dust/minerals in tropical environments brings about greater dissolution of rocks and minerals under high temperatures and moisture regimes. Use of rock dust in conjunction with composting, green manures, bioinoculants, microbes and mycorrhiza increases the solubilisation on nutrients and availability to plants.

METHOD AND RATE OF APPLICATION

Like any other organic amendments, biochar can be applied to soil by different methods including broadcasting, band application, spot placement, deep banding or deep placement. Mixing of biochar with composts and manures may reduce odours, and improve nutrient performance over time due to slower leaching rates. Mixtures may be applied for uniform topsoil mixing, or top-dressed in tree plantations without incorporation
Given the variability in biochar materials, nature of crop and soils, users of biochar should consider testing several rates of biochar application on a small scale before setting out to apply it on large areas. Experiments have found that rates between 5-50 t/ha have often been used successfully. Trials for standardization of doses for various crops in the state are to be conducted.

BIO FERMENTS

Bio ferments are products obtained from the decomposition of organic matter. In this process effective microorganisms are important because they break down the organic matter thus releasing nutrients for plant growth. Bio ferments can be prepared in the farm at a low cost using animal dung and other crop residues from banana and legumes.
Production of compost using Effective Mountain Micro organisms is an alternative for small scale farmers to regenerate the fertility of their soil. This technology was implemented for the first time in Japan 20 years ago. This practice requires extraction of microorganisms from their natural habitat (nearby natural forest) and are multiplied using locally available inputs and easy techniques. These microorganisms are then incorporated in the preparation of organic solid fertilizers (Bokashi) and Bioles (fermented liquid fertilizers), in order to regenerate deteriorating soil health due to faulty agricultural practices
Bokashi – A fermented mixture of solid organic materials acted upon by microorganisms to realize nutrients that are important for crops. When applied to soil, the microorganisms help to restore soil life and minimize incidences of crop diseases thus producing healthy crops with vigorous growth and high yields.
Bioles - A fermented liquid organic fertilizer produced from organic liquid material acted up on by effective Mountain Microorganisms, such as yeast, fungi and bacteria. The liquid organic matter is then transformed into plant elements, vitamins, organic acids and other substances for plant growth. It is applied as foliar spray on crop and the nutrients are absorbed immediately. Enrichment of bokashi and bioles can be done by adding the calculated quantities of the desired nutrient (Phosphorus, potassium, calcium, magnesium, borax, silicate etc) either alone or in combination.

Root Health

Effective foraging space of the plant roots, which is determined by the depth and lateral spread of the root system significantly influences the growth and yield of crops. Maintenance of a healthy root system is important from the point of view of proper anchorage, uptake of water and nutrients which are crucial for improving production and productivity of crops. It has been estimated that 80% of all plant problems start with soil/root problems. The roots of most plants are prone to attack by pathogenic fungi and nematodes, but the effects of such organisms may go unnoticed unless the attack is sufficiently severe to cause crop failure.
The strategy of seed treatment to protect plants from yield-reducing diseases by pathogenic organisms is gaining popularity. This practice enables development of healthier and stronger root systems, thereby helping the plants grow to their maximum genetic potential. Stronger, healthier roots can better uptake water and nutrients, two of the most critical resources a plant needs. This leads to better crop development at critical early stages and under a wide range of conditions. More robust root systems help produce stronger stems and foliage that better withstand environmental stress, especially in challenging climates. They protect the genetic potential of the crop and, ultimately, lead to improved yield consistency.

Root health assessment and rating

In root health assessment, the quality and function of the roots as estimated by observing the size, color, texture and absence of symptoms of damage by root pathogens. Appropriate indicator plants are grown in a portion of the soil sample in the greenhouse for a definite period to assessing the above parameters and the extent of damage by major pathogens. The plants are removed from their containers and the roots washed under running water and rated for root health on a scale to assess the extent of damage.
The basic protocol for assessing root health for various crop production systems in Kerala has to be standardized and it should be a component of a comprehensive soil health assessment report.

Soil health strategies for sustaining crop production in Kerala

The crop production scenario in Kerala is confronted with serious problems in respect of all the food crops as is evident from the steady decline in yield observed over the years. Soil degradative processes like water erosion, indiscriminate fertilizer use and low fertilizer use efficiency have been cited as the major reasons for the low productivity of soils and crops. The project on “Soil Test Based Nutrient Management Plan for Agro-ecosystems of Kerala” implemented by the Department of Agriculture also brought to focus the soil fertility constraints of the State in respect of acidification, high levels of phosphorus, extensive and widespread deficiency of Ca, Mg and B and deficiency of sulphur, copper, and zinc in limited areas. The current situation recognizes the need for reorientation of the soil testing including soil health parameters and initiate appropriate corrective measures to restore soil health, improve production and productivity of crops and sustain yield levels. The following issues and field level interventions are suggested for sustaining soil health and crop production.

• Soil testing services now are undergoing a major shift in emphasis from testing of individual nutrient elements required in plant nutrition to a holistic approach to encompass soil health. Reorientation of soil test parameters including physical and biological parameters are also needed for assessing soil health.
• The alarming situation on soil acidification and nutrient imbalances and reduction in carbon stock brought out in the soil fertility project along with physical degradative processes of water erosion, anthropological activities and soil moisture stress have deleterious effects on the soil biological community also needs specific attention.
• Studies on rhizosphere, below ground biodiversity and root health are areas which have not received any attention. In-depth studies on these areas have to be taken up to identify problems on the declining trends in the soil productivity and crop production.
• Linkages have to be established with agricultural research institutions to evolve soil health indicators relevant the soil and crop situations of the State and for appropriate soil health management interventions.
• The recent studies using VAM and Trichoderma in vegetable production have created renewed interest on bio fertilizer use. Several successful on farm production units operated by Self Help Groups are extending this cost effective technology to farmers.
• Ecological soil management practices like organic matter management through organic manures, green manuring (including in situ), cover cropping, crop rotations, residue management and restricted tillage have to be given priority to improve organic matter status, carbon sequestration, microbial biodiversity and soil physical condition which are all vital for sound soil health.
• Best management practices have to be identified for each agro ecological unit and implemented in the field so as to reverse soil degradation, promote economic benefits in production, and improve food and nutritional security and health of the people.