Grassland Production and its Relationship with Soil

Introduction
It is said that we are what we eat! As a generalisation this may be true and increasingly, in human nutrition, concerns are being raised as to the nutritional value of what we eat. The blame for the lowered value of our foods is being laid at the door of mono-cultural and intensive systems of farming. Another factor involved is the level of processing our food undergoes.

Certainly, the farming conditions in which we keep our alpacas make them dependent upon us for what they eat. In South America on the Alto-Plano they are, for the most part, free ranging and able to select their food, be it plentiful or sparse, grazing and browsing at will. Their ability to range offers them the opportunity to select different foods in different locations, thereby raising the chances of meeting their variable needs. Camel’s milk is “rich” in the essential life elements!

Goats and donkeys, among others, are the most selective grazers able to “choose” their food according to need. In the less intensive systems of yesteryear it was not uncommon that farmers kept goats or a donkey with dairy cows as a way of ensuring that they grazed more selectively as the “selective” donkey led them to areas where the grazing improved their fertility and production, because they were getting the best trace element pasture. Not a feature of modern dairy farming!

Alpacas’ needs are probably genetically derived from the land and soils where they originated and grazed. When we bring these animals into the UK we are placing them into environments where their ability to meet their needs is impaired through confinement. They are conditioned by their origins to need specific levels of nutrients and may be unable to assimilate sufficient of some or take in excess of others depending upon circumstances.

We need to bear this in mind when we examine our management of grassland for alpacas and take trouble to look deeper than just the production of large quantities of lush green grass, desirable though that may be. If we are what we eat, so is a plant, and the source of food for all plants is of course the soil in which it is rooted or planted. Soils are complex media consisting of the parent material, its structure and mineral particles, water and air, organic matter and nutrients, and biological activity in the form of bacteria, fungi etc without which soils would be relatively sterile and inert. It seems pertinent therefore to take a brief look at soils.

Soil—Our Raw Material
Soil management is aimed at growing a profitable crop, improving the soil’s fertility and preventing environmental damage. We need to provide a suitable medium in which seeds can germinate, develop root systems and achieve growth from nutrients supplied by the soil. We need to control weeds and prevent the build up of diseases.

Traditionally all of these were achieved by crop rotation, grass being the part of the rotation that improved the soil’s physical condition and its fertility from grazing stock manuring it. The arable cultivations were the part of the rotation controlling weeds and the changes of crop controlled the disease build up. Fertility was improved if stock were folded on arable root crops. Nowadays much more intensive use is made of land, and land is farmed in looser rotations with periods of monoculture. The advent of chemical weed control and fertilisers meant that weeds could be controlled without cultivations and production could be achieved with the use of fertilisers. Digging a pit to view the soil’s profile is a most useful method of examining the structure of a soil and exposing any problems. Examination of the layers of soil can give indications of compacted layers or “pans”, which impede both drainage and root development. Soil that is brightly coloured without mottling or grey areas is well drained. Dull colour and “gleying” (grey colour) indicates poor drainage. Soil texture is the most important property of a soil. It is determined by the mixture of particles of different sizes, be they gravel, sand, silt or clay in a particular soil. The texture of a soil determines its drainage, water storage, working properties and suitability for different crops.

Water and air have to be present in soils for crops to grow successfully. Large reserves of water are needed in summer to meet a crop’s requirements, but too much water excludes air and roots fail to develop or die through lack of air. The best soils are those that drain freely but retain sufficient moisture to meet crop needs in summer. For example, a deep clay loam will have sufficient larger sized particles to drain effectively, but also the smaller clay particles are able to retain moisture in depth and that allows deep root development, which is then able to tap those water reserves when needed.

Organic matter or “humus”, which is decomposed plant and animal material, has an effect on soils that is far greater than its small amount in soils would at first indicate. It contains nutrients and provides stability to some soils whilst in others it improves workability. It also contains living organisms from the smallest bacteria through fungi, plant roots and insects to earthworms and soil pests. This biological fraction is vitally important to the living processes in the soil, such as rotting and nitrification. Desert soils are slow and difficult to recover because this biological factor of fertility is missing and only builds up slowly. Seeds fail to germinate and plants exhibit strange colours and stunted growth until minimum levels are achieved.

Clay and organic matter have the ability to hold or “adsorb” water-soluble nutrients, making them available to plant roots. This property also reduces the loss of nutrients in drainage water, which is known as “leaching”. Adding fertiliser to a soil allows its nutrients to exchange with those held by clay and organic matter. These nutrients are “bases” (they have the ability to neutralise acids) and the most important of these is calcium. A soil’s ability or capacity to exchange nutrients is reflected in its alkalinity or acidity. Neutral soils are saturated with bases (mainly calcium) but acid soils are depleted of calcium. Most crops will not tolerate very acid soils but developing acidity can be corrected today by liming, which is the adding of calcium. Acid soils tend to be short of nutrients and “hungry”.

Plant nutrients that are essential to successful growth are divided into “major nutrients”, which are required in relatively large amounts, and minor nutrients, which are required in lesser amounts, some only at trace levels. Some nutrients are soluble in water and can be washed out of the soil by heavy rain and others are less soluble and leach only slowly. Some nutrients are loosely adsorbed, whilst others such as phosphate are strongly adsorbed.

Only a small part of the total nutrients in a soil is readily available to be absorbed by the crop’s roots. This “available” nutrient is replaced slowly from soil reserves as the crop uses it up. However, major nutrients like nitrogen, phosphorus, and potash have to be regularly applied to meet crop requirements, where high yields are sought. The use of manufactured fertilisers has met this requirement. It is often argued that organic fertiliser is safer and better than manufactured fertiliser, indeed it does carry benefits with it in soil conditioning and storage of nutrients, but it remains a fact that organic fertiliser has to be broken down by bacteria in the soil to the same inorganic form as manufactured fertiliser before the plant can utilise it.

Soil Fertility and Grass Production
Liming acid soils brings great benefit to grass growth. Most grasses thrive in slightly acid soils; a satisfactory pH is 6.0 so there is no need to attempt to achieve neutrality (pH 7.0). The provision of calcium in lime sweetens the soil in that it does two things. Firstly, as we have seen, it improves the conditions for nutrient exchange and thereby plant uptake. The provision of calcium is vital for growth in the development of plant cells. Grass contains significant quantities of calcium and legumes are particularly sensitive to calcium deficiency. Secondly, it improves the soil structure especially on clay or heavy textured soils by causing the clay colloids (very fine particles) to flocculate and clump together developing a crumb like structure. This improves the workability of heavy soils. Acid soil conditions have an influence on the availability of nutrients. Some trace elements are less available under acid conditions, such as iron, boron, copper and molybdenum. (See chart) Liming under these conditions reduces the chances of deficiency in plants and grazing animals.

Conversely, alkaline conditions will affect the availability of other elements, such as phosphorus, potassium, manganese, boron, copper and zinc. Thus over liming (less common than under liming) can have serious consequences in making these elements less available to plants and grazing animals alike, inducing trace element deficiencies. The following trace elements are essential to grass growth: iron (Fe), manganese (Mn), boron (B), copper (Cu), zinc (Zn), molybdenum (Mo), and chlorine (Cl). Most of these are also needed by animals with the addition of cobalt (Co), iodine (I), and selenium (Se), which plants take up but don’t actually need.

Acid soils tend to encourage lower value grasses and clovers will be weak and sparse; with less earthworm activity, biological activity in general is lower, encouraging a mat of slowly decaying organic matter to accumulate locking up nutrients. The taking of hay and silage crops removes calcium from the soil in small amounts but the use of modern nitrogenous and compound fertilisers, which have no calcium in them, has a far greater acidifying effect on soil.

It therefore pays to test soils for pH in order to get it right and calculate the correct amount of ground limestone to apply. This can be done for you by local advisory services, or agricultural merchants, or even by buying a test kit from a garden centre. If you suspect that you may have trace element deficiency problems with alpacas, you should take soil samples from your fields (minimum ½ litre) and go to a laboratory where they can test for pH, phosphorus and potassium and trace element levels.

Soil sampling technique is simple but a few rules apply. Take samples from a representative cross section or transept of your land, walk in a W or zigzag pattern. Take between 10 and 30 samples from an inch below the surface down to 2-3 inches deep and mix them. Take professional advice about interpretation of the results as the interactions of pH, and other elements is complex. Ad hoc application of trace elements is dangerous as excess application produces toxicity, which may be far harder to remedy than the deficiency. Given a properly balanced diet the grazing ruminant is able to remain immune to most diseases and malfunctions. Very good fertility and production can be maintained with very little support from drugs, medicines and other devices!

Amen to that!

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