Soil health, also referred to as soil quality, is defined as the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans. This definition speaks to the importance of managing soils so they are sustainable for future generations. To do this, we need to remember that soil contains living organisms that when provided the basic necessities of life - food, shelter, and water - perform functions required to produce food and fiber. Only "living" things can have health, so viewing soil as a living ecosystem reflects a fundamental shift in the way we care for our nation's soils. Soil isn’t an inert growing medium, but rather is teaming with billions of bacteria, fungi, and other microbes that are the foundation of an elegant symbiotic ecosystem. Soil is an ecosystem that can be managed to provide nutrients for plant growth, absorb and hold rainwater for use during dryer periods, filter and buffer potential pollutants from leaving our fields, serve as a firm foundation for agricultural activities, and provide habitat for soil microbes to flourish and diversify to keep the ecosystem running smoothly.
Knowledge of how soil pH profiles and acidification rates vary across the farm will assist effective soil acidity management.
Ideally, soil samples should be taken when soils are dry and have minimal biological activity. It is standard to measure pH using one part soil to five parts 0.01 M CaCl2. Soils with low total salts show large seasonal variation in pH if it is measured in water. pH measured in water can read 0.6 – 1.2 pH units higher than in calcium chloride (Moore et al., 1998).
Soil sampling should take paddock variability into consideration. For example, clays have greater capacity to resist pH change (buffering) than loams, which are better buffered than sands. Samples should be taken at the surface and in the subsurface to determine a soil pH profile. This will detect subsurface acidity, which may underlie topsoils with an optimal pH.
Samples need to be properly located (e.g. GPS) to allow monitoring. Sampling should be repeated every 3 – 4 years to detect changes and allow adjustment of management practices.
Depending on soil pH test results, agricultural lime may need to be applied to maintain pH, or to recover pH to an appropriate level. If the topsoil pH is above 5.5 and the subsurface pH above 4.8, only maintenance levels of liming will be required to counter on-going acidification caused by productive agriculture.
If the topsoil pH is below 5.5, recovery liming is recommended. Keeping the topsoil above 5.5 will treat the on-going acidification due to farming and ensure sufficient alkalinity can move down and treat subsurface acidity.
Liming is necessary if the subsurface pH is below 4.8, whether or not the topsoil is acidic. If the 10 – 20 cm layer is below 4.8 but the 20 – 30 cm layer above 4.8, liming is still required. In this case the band of acidic soil will restrict root access to the more suitable soil below.
Liming is the most economical method of ameliorating soil acidity. The amount of lime required will depend on the soil pH profile, lime quality, soil type, farming system and rainfall.
Limesand, from coastal dunes, crushed limestone and dolomitic limestone are the main sources of agricultural lime. Carbonate from calcium carbonate and magnesium carbonate is the component in all of these sources that neutralises acid in soil.
The key factors in lime quality are neutralising value and particle size. The neutralising value of the lime is expressed as a percentage of pure calcium carbonate which is given a value of 100 %. With a higher neutralising value, less lime can be used, or more area treated, for the same pH change. Lime with a higher proportion of small particles will react quicker to neutralise acid in the soil, which is beneficial when liming to recover acidic soil.
If soil pH is low, using tolerant species/varieties of crops and pasture can reduce the impact of soil acidity. This is not a permanent solution because the soil will continue to acidify without liming treatment.
A number of management practices can reduce the rate of soil acidification. Management of nitrogen fertiliser input to reduce nitrate leaching is most important in high rainfall areas. Product export can be reduced by feeding hay back onto paddocks from where it has been cut. Less acidifying options in rotations will also help, e.g. replace legume hay with a less acidifying crop or pasture.
Of the 17 essential nutrients, carbon, oxygen and hydrogen are classed as non-mineral elements. They are accessed from air and water and are therefore not considered soil nutrients. Carbon forms the backbone of many plant biological molecules, including proteins, starches and cellulose. It is fixed by photosynthesis (the process by which green plants use sunlight and chlorophyll to construct foods from carbon dioxide and water) from carbon dioxide and is a part of the sugars and starches that store energy in the plant. Hydrogen is obtained almost entirely from water. It is a critical element in photosynthesis and for respiration, the process of generating energy through the consumption of foods made by photosynthesis. Oxygen is gained from the air as oxygen gas or in the molecules of water or carbon dioxide. It is also necessary for plant respiration (the process by which the plant accesses energy from sugars and starches in the presence of oxygen). The remaining 14 elements are all classed as soil nutrients. They are divided into two categories: the macronutrients and the micronutrients.
The macronutrients, as the name suggests, are required in relatively large quantities. They are necessary for the basic, day-to-day plant biological functions such as growth, photosynthesis and respiration. The macronutrients are:
The micronutrients, while equally important as the macronutrients, are only required in small quantities. Deficiencies in micronutrients are more common in highly leached sands, organic soils and in highly alkaline soils. Deficiencies can also develop in intensely cropped soil. The micronutrients can be harmful or detrimental to plant growth if they are present in large quantities. The CSIRO publication, Australian Soils and Landscapes; An Illustrated Compendium, notes that the agricultural development of large areas of Australia was only possible when micronutrient deficiencies were recognised and remedied. The current recognised essential micronutrients are:
In addition to the essential nutrients, there are a number of elements that do not fully meet the strict definition of essential but which are, nevertheless, important. These elements are either essential to some, but not all, plant species or they are highly beneficial to plant growth. It is important to note that as our scientific knowledge of plant nutrition grows so does this list of elements. Some of the nutrients in this category are:
Speak with a human to filling out a form? call corporate office and we will connect you with a team member who can help.
WHY CHOOSE
We support the Government of India’s Soil Health Management Scheme and Soil Health Card Scheme. We encourage all organic producers to register and get their soil tested. Knowing the quality of your soil, is the first step towards its healing.
