Phosphate and Clovers

New Zealand Journal of Agriculture, Volume 79, Issue 3, 15 September 1949, Page 271

Phosphate and Clovers

By

P. D. SEARS,

Grasslands

Division, Department of Scientific and Industrial Research.

DURING the recent period of the high cost of phosphatic fertilisers farmers have had to look more carefully at their fertiliser programmes. Especially is this so in hill-country districts where the cost of hand topdressing is also increasing and is apparently militating seriously against development of this hill country.

IMPORTANT as is the correct use of phosphate in pasture growth it is nevertheless a fact that quite a large proportion of farmers have unbounded faith in superphosphate and think that the only requirement for good pasture growth is the application to their farms of large quantities of phosphate, come what may. This misconception seems to prevail throughout the country and is clearly evident from discussions both on farms and at farmers’ meetings as well as from practices seen in the field. It can be claimed, of course, that such an attitude is logical, because it is justified by some of the splendid results which have been and are being obtained from the use of phosphates on grassland. However, high costs, limitation of supplies, and added difficulties of delivery and application to paddocks all call for very careful consideration by the individual farmer of the particular conditions on his own property.

The need for this very careful consideration becomes more obvious when one hears so much criticism by some farmers of the lack of efficiency in those industries servicing them in the supply, manufacture, and delivery of phosphatic fertilisers.

What Trials Showed

For the past few years the Grasslands Division of the Department of Scientific and Industrial Research has conducted a comprehensive series of field and laboratory trials on the grassland fertility cycle. They have yielded

a large volume of data from which a definite pattern of action can be taken for use in the field. A good starting point from which to consider the Grasslands Division investigations is a trial designed to measure the manurial value of dung , and urine and their effects on the sward. The results of this trial, in which sheep were used on a high-production sward, showed that the annual value of the dung and urine per acre was equal to about a ton of sulphate of ammonia, 17cwt. of potash salts, Bcwt. of superphosphate, and 4cwt. of carbonate of lime. Most of the nitrogen and potash was contained in the urine, which stimulated the grass growth, whereas all the phosphate and lime and some nitrogen and potash were contained in the dung, which mainly gave extra clover growth. (Full-grown dry animals, which retained practically no plant nutrients, were used in these trials. Other classes of stock retain greater amounts of plant nutrients for their own use, but over all'the amount retained is small compared with the total turnover of soil fertility ingredients by the grazing animal.) Addi-

tional measurements showed that the greater proportion of the dung and urine was passed at night and it is therefore easy to transfer soil fertility by differential day and night grazing. Similar effects have been .measured on hill-country trials, which 'show clearly the fertility transference going on within paddocks because of stock grazing and excretion habits. . > Next for consideration is a trial in which the effect of clovers in the sward and of added phosphate on this sward is measured. Full details of this trial cannot be given here, but the results are set out briefly in the table on this page. The pastures without clover which received no phosphates or to which no animal manures were returned used up the initial high soil fertility rapidly and reverted to browntop, chewings fescue, and weeds, producing altogether approximately 18001 b. of dry matter, of about 13 per cent, crude protein, per acre. Such pastures, which are very similar to millions of acres of farmed pastures in New Zealand, have a carrying capacity of about 1 sheep per acre.

The addition of 6cwt. of superphosphate per acre per annum for the past 3 years, plus 1 ton of lime per acre, to the trial pastures which contained no clovers has brought about no worthwhile increase in production over the untopdressed series of pastures. On the other hand swards of the same

grass sowings which included white and red clovers but which re-

ceived no fertiliser have given an annual yield of some 90001 b. of dry matter with a crude protein yield of 28 per cent. This would carry about 7 to 8 sheep per acre.

Where the grass and clover combination had phosphate and lime applied, a yield of approximately 12,0001 b. of dry matter with a crude protein yield of 26 per cent, was produced per annum, representing an increase of about 23 per cent, per annum due to the fertilisers. As can be seen from the table, none of the swards mentioned above received dung or urine from the animals grazing them, as it was collected in special apparatus and discarded. Thus a phosphate deficiency was developed in the soil, but it is important to note that added phosphate was effective in producing extra growth only where the clovers were present, because in the pure grass swards growth was limited by an inadequate supply of nitrogen, and the addition of such large quantities of phosphate as were applied made no difference to the pasture growth. However, in pastures where the nitrogen supply was adequatewhere clovers were present in the sward addition of phosphate increased production considerably. In another series of pastures similar to the first, but where dung and urine were returned by normal grazing, neither the pure grass swards nor the mixed grass and clover swards showed response to added phosphate except for a slight increase in the winter growth of the grass in the mixed swards. However, all swards in this latter series showed a much higher yield, especially the grass constituents, than their counterparts in the series not receiving dung and urine. This increase in grass production resulted not only in greater annual total production from the sward, but also in a better balance between grass and clover and . a much better seasonal spread of production more suited to animal feed requirements. The lack of response to superphosphate in the series of trials where dung and urine were returned by normal grazing was due to the amount of available phosphate in the soil initially quite highbeing kept stable by the return of dung. Extra phosphate in the form of superphosphate was not therefore needed. There was, however, a slight increase in winter grass growth on phosphated swards. This could be explained by the greater availability of phosphate in superphosphate than in dung at a time when soil temperatures probably are too low for maximum activity among soil organisms which break down dung to form plant food. s Hill-country Tria!

A trial very similar to that last mentioned, except that it was carried out on large hill-country paddocks near

Palmerston North, showed a striking increase (approximately 100 per cent.) in the production of the sward when superphosphate was applied. and an oversowing of clovers made. Where the same amount of superphosphate was applied (a total of 6cwt. per acre over 3 years) without the sowing of clovers there was virtually/ no improvement either in the yield, composition, or palatability of the pasture. Other trials and observations made throughout the country on both flat land and hill-country farms all show much the same trend: There is very limited response to added phosphate except where the nitrogen supply has been built up. This can be accomplished primarily by the use of clovers or in various other ways; for example, by the use of animal manures, artificial nitrogenous fertilisers, or by cultivation in a fallow. The last method not only destroys weed growth, but also aids in the breaking down of organic matter in the soil and the building up of a supply of nitrogen which can be used by the crop following the fallow. When interpreted for practical application the results of these trials agree well with the advice which has been given for many years as an outcome of results obtained from practical farming experiences. It is essential to get clovers into all pastures. All clovers are good, but some are better than others, the New Zealand pedigree strain ■of white clover being of outstanding value. This species can be introduced in many ways, from ploughing and sowing on a good seed-bed right through to a simple oversowing on the existing sward. Successful establishment in all cases will depend on many factors, but the few failures which have occurred in attempting to introduce this key species into the sward are well outweighed by successes.

Clovers Need Feeding

To do their job of fixing nitrogen and producing growth, clovers need feeding. Phosphate, the main mineral deficiency in New Zealand, will be-the most likely requirement, but in some places lime and/or potash will be needed in addition to, or instead of, the phosphate. In some extremely-poor soils it may even be necessary to use a little nitrogen to start the clovers. It is also necessary to let clovers grow—constant nibbling away at these plants or allowing them to be overshadowed when they are young can kill them and undo all the good that has been done by their introduction into the sward. ' Vigorous growth of clovers benefits associated grass plants in the sward directly, but there is an even greater gain from the urine and dung of stock grazing on new growth. It is therefore essential that the return of dung and urine to the sward should be controlled so that each paddock receives back its true quota and the distribution on each paddock is as even as possible. The latter recommendation is not implemented easily, but practices such as harrowing, rotational grazing, elimination of “day” . and “night” paddocks, and careful placing of shelter belts, gates, and watertroughs are all advantageous. Shelter belts should be fenced off from stock to avoid undue concentration of the droppings of grazing animals.

After conversion of the new clover growth into dung and urine the latter will make the grass grow, but it may still be necessary to apply more phosphate to the pasture to get the maximum growth of the grass in the sward. This is because grass plants growing well take up more phosphate per acre than do clover plants, though that occurs only when grasses are adequately supplied with nitrogen.

It is possible, therefore, to get three separate responses from added phosphates: First, the response in the new grass sown on a soil in which the nitrogen has been built up by cultivation, etc.; second, the response of the clover, which can fix its own nitrogen; and third, the secondary response of grass which has been fed extra nitrogen by clovers and the dung and urine from grazing animals.

It will be agreed that the subject discussed in this article is not simple, but a solution of the problems mentioned must be worked out by each farmer on his own property, both because of initial differences in the phosphate content of the soil and differences in soil fertility due to variation in farming practice. The individuality of the New Zealand farmer is often quoted as one of his main attributes. In deciding what is the best manuring programme for a particular farm there is ample scope for exercising individual judgment.

Germination of Government-approved Seeds

Government-approved seeds, though produced under the supervision and bearing the official endorsement of the Department of Agriculture, do not carry on the container a reference to the official purity and germination certificate covering the seed. Blending of seed is undertaken, however, to ensure that all seed of a variety is uniform in quality for the season, and the following are the germinations of the various lots of Government-approved seed being distributed for sowing in the spring of 1949: SWEDE SEED: Grandmaster a Crimson King I All 90 per cent, or Resistant I better Calder ' Superlative 83 per cent. Sensation 74 per cent. YELLOW-FLESHED TURNIP SEED: Green Top Yellow \ S °v o H„ r ® en Top ' All 90 per cent, or Yellow better Green Resistant 1 Dener Purple Top Yellow. /. Purple Resistant 83 per cent. WHITE-FLESHED TURNIP SEED: Green Globe I A „ 90 per cent, or I THOUSAND-HEADED Over 00 per cer,tKALE SEED: uver ju.per wm. All lines except Sensation swede seed show good germination. The germination of the Sensation swede seed, though lower than the others, is sufficient to give a satisfactory strike under normal conditions. If conditions at time of sowing are unsatisfactory, however, a slightly-increased sowing rate may be desirable.

Treatment Total dry matter (lb.) Grass (lb.) White clover (lb.) Red clover (lb.) Other species (lb.) Crude protein (lb.) Weight PO S in herbage (lb.) Percentage PO_ in herbage No Return of Dung and Urine Grass, no clovers, no fertiliser .. .. . . 1,777 1.760 17 269 18 1.01 Grass, no clovers, -j- lime and superphosphate' - 1,888 1,843 - - —_ ■ —— 45 275 22 .16 Grass 4- clovers, no fertiliser .. .. 9,425 4,017 4,154 1,162 92 2,398 92 0.98 Grass + clovers + lime and superphosphate 11,592 4,564 6,077 932 19 3,192 131 1.13 Return of Dung and Urine Grass, no clovers, no fertiliser .. 6,434 6,276 . . -- ■ ■' ■ • 158 1,250 75 1.17 | Grass, no clovers + lime and superphosphate 6,183 6,119 _- __ - 64 64 1,240 1,240 79 79 1.28 1.28 1 Grass + clovers, no fertilisers . . 15,830 10,255 ' 5,469 58 48 4,524 177 1.12 \ Grass -J- clovers + lime and superphosphate 15,518 9,893 5,544 57 24 4,452 180 1.16

YIELD AND COMPOSITION OF PASTURES UNDER DIFFERENT TREATMENTS (Period January 14, 1948, to February 14, 1949.)