Initial Fertiliser On Hill Country

Press, Volume CVI, Issue 31125, 30 July 1966, Page 9

Initial Fertiliser On Hill Country

The question of how much, and which type of fertiliser to use for initial and maintenance topdressings of hill country, is one which is assuming increasing significance as we look more and more to hill country for increases in production. This article deals with some of the considerations in applying initial dressings of fertiliser to hill country in North Canterbury.

1. pH Levels. Ideally pH levels should be greater than pH 6.0 However typical pH figures in native hill country in Canterbury are from about pH 5.0 to pH 5.8, depending on the rainfall and type of soiL (pH 5.0 could be expected on cold rolling country in higher rainfall areas, whereas pH 5.8 could be expected on steep soils in a 25in rainfall area, where, because of the low rainfall and the steep nature of the country, the soils are kept and rejuvenated by gradual movement downhill.) The effect of lime is to raise this pH and by doing so to make many elements more readily available to the plant. This is particularly important as far as the trace element molybdenum is concerned. However applications of lime by air are very expensive and, although it may be possible to lime aerially more cheaply in the future, we can overcome the problem, at least partially, by applying the trace elements with the fertiliser, that is, molybdenum. Problems of higher rates of phosphate fixation in the low pH soils are probably more cheaply rectified by higher rates of super. 2. Nitrogen. Almost all our tussock grasslands are deficient in available nitrogen, but by far the cheapest way of rectifying this deficiency is through good strains of clover and therefore fertiliser applications should be aimed at creating a suitable soil mineral status for clover growth. Generally this involves mainly phosphorus and sulphur. 3. Phosphorus. Department of Agriculture soil tests on native hill country in North Canterbury have ranged in phosphate levels from about 2 to 8 on the Truog test (very low to moderate levels). When applying super the responses obtained may be partly or largely due to the sulphur in super. Super contains 101 b of phosphorus per cwt and 12.51 b of sulphur per cwt. By applying 20401 b of phosphorus per acre (2-4 cwt super), the phosphorus will normally be raised to satisfactory levels for clover growth. The amount to be

applied depends primarily on the initial phosphate levels which can be obtained from soil tests. 4. Sulphur. Sulphur deficiencies are more likely to occur in areas away from the sea. Ordinary superphosphate contains as much sulphur as it does phosphate.

From the table it can be seen that the cheaper way to apply sulphur is through sulphur super. This is further emphasised when transport and flying charges are allowed for. However, this is not the only consideration. All sulphur in ordinary superphosphate is in the form of gypsum, which is more soluble and hence more readily available to the plant than the sulphur in its elemental state. This assumes more importance in a low rainfall area where, because of the relatively insoluble nature of the elemental sulphur, the full extent of the response is likely to be delayed (depending on the rainfall after application). From demonstration plots put down in North Canterbury last year, the extent of this delay appears to be about two to three months. An important factor in this regard is the fineness of grinding of the elemental sulphur. Another consideration is the residual effect of sulphur. In a high rainfall area the sulphur in gypsum will have little residual effect whereas the elemental sulphur because of its relative insolubility, will continue to release sulphur available to the plants for a longer time. If the main deficiency is sulphur (n.b. phosphate levels can be obtained from soil tests) it is much cheaper to apply sulphur super. To apply 751 b of sulphur per acre requires 6cwt of ordinary super or 2.scwt of

sulphur super (4001 b mix); to apply 501 b of sulphur per acre requires 4cwt of super or I.6scwt of sulphur super (4001 b mix). Some idea of the cost is as follows:

If 2]cwt of sulphur super will give a similar response to 6cwt of super this would represent a saving of £2 8s 6d per acre, Le. £l2l for a 50-acre block. If I.6scwt of sulphur super will give a similar response to 4cwt of super this would represent a saving of £1 12s 6d an acre, Le. £Bl for a 50-acre block.

Apart from the residual effects and the time delay factors, the question of whether to use sulphur super or ordinary super depends on the relative severity of the phosphate and sulphur deficiencies, Le. a range from sulphur fertilisers through to phosphate fertilisers.

Thus with severe sulphur deficiency and no phosphate

deficiency, the appropriate fertiliser is straight sulphur. Severe sulphur deficiency and moderate phosphate deficiency, sulphur super. Moderate sulphur deficiency and similar phosphate deficiency, ordinary super. No sulphur deficiency and severe phosphate deficiency, triple super (Le. a high percentage of phosphorus). 5. Potash: Although it is not common in Canterbury certain factors may lead to a potash deficiency. Those affecting the potassium status of the soils are firstly, the parent mater-

ial from which the soil is derived. Secondly climatic factors such as rainfall and temperatures, which determine how fast the soil minerals break down to form clays and release their potassium. Thirdly the farming history of the soil, Le. a potash deficiency is not likely to develop under grazing conditions, as the returns are high, but is more likely to develop under continuous cropping, or in the case of haying, where a paddock is used specifically for hay with no potash returns through grazing of fertilisers. The soils of Canterbury generally have a high content of day minerals with a high potassium supplying power. Therefore under normal farming conditions it is

unusual to get a potash response.

6. Molybdenum. Molybdenum Is necessary for nitrogen fixation by clover. Lime, by raising the pH, generally releases enough molybdenum for this, but where, on hill country, liming is not really practical, applications of molybdenum may be warranted. (Molybdic super is not expensive and it is usually a good insurance policy to apply it) Molybdic super normally contains loz of molybdate per cwt Responses have been obtained up to Boz per acre at Waiau, but generally two to three ounces would be sufficient Molybdenum application needs to be looked at very carefully if being applied at high rates or if the copper status of the soil is low. 7. Copper. There are only a few instances where copper deficiency has occurred in North Canterbury. Diagnosis is normally done by liver analysis and five pounds of copper sulphate per acre should rectify copper deficiencies.

8. Conclusion. The question of how much and which type of fertiliser to use as an initial topdressing for aerial hill

country development is a very difficult one. On this question and the question of maintenance requirements, much experimental work is being carried out, and a start has been made on a national scale by the research division of the Department of Agriculture. However until we have concrete evidence, the soil type, rainfall, location and other factors can all be used to make an intelligent guess.

The accompanying article has been written by Mr M. J. H. Davison, a farm advisory officer of the Department of Agriculture at Rangiora

lbs per cwt Super Sulphur Super (4001b sulphur) Phosphorus H ►- 10 8.2 Sulphur (as Gypsum) M r 12.5 10.2 Sulphur (as element) M IP! 20 Total Sulphur M W 12.5 30.2 Cost per bulk ton . M »1 £10/10/6 £13/12/Cost per lb sulphur W lO.ld 5.4d

Super per ton S/Super (400 mix) per ton £ ■ d £ s d 10 10 6 bulk 13 12 0 bulk 2 0 0 freight 2 0 0 freight 3 10 0 flying 3 10 0 flying £16 0 6 per ton £19 2 0 per ton “ 16/- per cwt - 19/1 per cwt Sulphur Phosphorus Applied Applied Cost lbs lbs Per Acre 6cwt super m m 75 60 £4 16 0 2.5cwt s/super M n] 75 20J £2 7 6 4cwt super 50 40 £3 4 0 1.65cwt s/super . »• 50 13$ £1 11 6