What super-phosphate does for your pasture

Ruapehu Bulletin, Volume 6, Issue 288, 30 May 1989, Page 4

What super-phosphate does for your pasture

by

jlm

Galloway

(b.agr.sc)

barmers have been applying these two major elements to their pastures for many years in super-phosphate, and have seen large increases in pasture and animal production as a result.

How many realise just how these elements influence performance? They both have an influence on pasture and animal production. Why use Phosphate and Sulphur? The myth that N.Z. soils are fertile is just that, a myth, In general, NZ soils are young and have a low nulricnt status, as there has bccn little weathering of the parent material. The soiis in NZ generally cannot supply enough phosphate and sulphur because: • More dry matter is grown than would be in natural vegetation. • Continual transfer of nutrients from the land (meat, wool, milk etc). • Transfer of nutrients to stock camps. • Erosion and leaching is acceleratcd by development, thcrcby increasing losses. • The soil locks up some phosphate and. sulphur into unavailable forms. Phosphorous Phosphorous is one of the most important elements to all living organisms, especially of plant life. Phosphorous is the main requircment for ihe production of energy in the cells of all living organisms. The energy is uscd to drive the biochcmical and physiological chains in the cells, without which cells and thercfore the body could not survive. With adequate phos-

phorous, plants will establish better and generally grow faster and larger than without adequate phosphorous. One of the major factors of adequate phosphate is improved root growth which helps plants to exploit the soil nutrients and water. This has a beneficial effect in dry seasons because plants, with good roots, will grow longer into a dry spell due to better water extraction. A good strong plant is also less susceptible to diseases. The availability of phosphate stimulates the bacteria associated with legumcs, which fix nitrogen. This nitrogen fixation is vital to the production of pastures in NZ where pastures obtain nitrogen through fixation rather than applied as nitrogen as in other countries. (NZ annually applies about 20,000 net as of nitrogen by fertiliser compared to about an estimated 1,000,000 tonnes by clovers). In the animal, phosphate, as well as for energy production in cells, is mainly used in the skeleton with 75-80% of the body phosphate being associated with the skeleton. Phosphorous is also an important constituent of milk. If the pasture has inadequate phosphate, milk production will suffer. Fast growing young cattle also require high phosphate pastures due

to rapid skeletal growth. Sulphur Sulphur is present in the soil mostly as soil organic matter (about 75-90% of all sulphur). This organic matter has to be continually broken down to release sulphate-sulphur which can be taken up by plants. This soil organic matter builds up over time. In newly developed pastures soil organic matter is low, so sulphur cycling is slow. This means that these pastures have a

higher sulphur requirement. More than three years cropping will deplete the organic matter to a stage where sulphur requirements are similar to that found on newly developed land. Sulphur is lost from the soil by: • leaching. • transfer to stock camps. • transfer off the farm (wool, meat, milk etc). • immobilisation by the soil. Leaching losses depend mainly on soil

type and rainfall. Free draining, medium to low sulphur retentive soils in high rainfall regions have high sulphur losses. Examples of these soil types include, yellow brown earths (mudstone type), pumice, alluvial soils; yellow grey earths and sands. Once the sulphur has been taken up by the plant it is used in the formation of enzymes and proteins which are essential to the plant growth. Sulphur is also important for nodule

formation on legumes so is also important for nitrogen production. Sulphur deficiency shows up first in clovers as they aren't as good as grasses at utilising sulphur. In the animal, most of the sulphur is present in the sulphur amino acids of proteins, including wool and hair. Sulphur is also present in cartilage, tendons and B vitamins. Wool is very high in sulphur and in every bale of wool approximately 5kg of sulphur is exported off the farm. The B vitamins are essential

for carbohydrate metabolism which is how animals get energy to operate their bodies. Summary Phosphate and sulphur are essential elements in both animals and plants. With loses that occur in the soil and with transfer of nutrients off pastures, farmers still need to apply sufficient amounts of phosphorous and sulphur to maintain their pasture and hence animal productivity. By maintaining this productivity, farmers take an important step in maintaining profitability.