SERPENTINE SUPERPHOSPHATE

New Zealand Journal of Agriculture, Volume 63, Issue 3, 15 September 1941, Page 177

SERPENTINE SUPERPHOSPHATE

Experiments with serpentine superphosphate have shown that, applied at the same rate as superphosphate on grassland, it has given equally good results in a number of districts, and the same effect is seen on

most of the common farm crops throughout the Dominion. The saving of phosphate where the new mixture is giving such satisfactory results ' under the conditions described is of considerable practical importance.

Recommendations tor Use Of the New . Mixture

By

A. G. ELLIOTT,

Crop Experimentalist, and

P. B. LYNCH,

Assistant Crop Experimentalist, Wellington.

AT the beginning of 1940 two factors made essential an immediate and comprehensive experimental programme with serpentine superphosphate—(l) the, promising results of preliminary trials with the new manure, and (2) the possibility of a shortage of phosphatic fertilisers, later to become an unpleasant reality. Data from a large number of trials is now sufficiently complete to make possible an estimate of the value of , serpentine superphosphate and to give recommendations regarding its use. Early Work In the “Journal” for April, 1940, an account is given of the history of the

material and the workers associated. with its early development. Interest in the possibilities of serpentine was aroused as a result of Russian investigations into the mixing of dunite (a rock usually containing the mineral serpentine) with superphosphate. Various Divisions of the Departments of Agriculture and of Scientific and Industrial Research in New Zealand then 'co-operated with superphosphate manufacturers to produce small quantities of a superphosphate serpentine mixture, and a preliminary experi-

mental programme was begun. The indications from this work were sufficiently promising to ' warrant the comprehensive investigation that was subsequently carried out. ; ; While much work has been done on the manufacturing details and on the chemical behaviour of the mixture, it is intended to restrict the present article to a description > of the practical value of serpentine superphosphate to farmers, and to summarise the results of trials carried out by the Fields Division.

What Is Serpentine Superphosphate?

The name serpentine superphosphate will be used in future in place of “silico superphosphate,” as it is a more accurate description of the material. It is made by mixing three parts of hot, newly-made superphosphate with one part of ground , serpentine and allowing the mixture to “mature” in heaps for several days. Reversion of the water-soluble phosphate of superphosphate then occurs, with the production of, a form of phosphate insoluble in water but soluble in soil water. Soil water contains small amounts of dissolved substances, and is generally acidic in nature, so that many substances will go into solution in the soil when they will not dissolve in pure water. A weak solution of citric acid is used in the laboratory to estimate the proportion of the material which will dissolve in soil water, and the following typical analyses show what happens when reversion takes place. . x : Serpentine Super- Superphosphate. phosphate. Percentage total phosphate (PO 5 ) ■ 23.8 16.4 Percentage citric-soluble •phosphate(P 2 23)O 3 ) .. .' 13.5 Percentage water-soluble phosphate(P 2 25)O 5 ) .. 19.9 2.6 The lower percentage of total P 205 is due to the fact that serpentine contains no phosphate. Thus, on the basis of the total amount of phosphate, three parts of superphosphate are equivalent to about four parts of serpentine superphosphate.

Certain Advantages

Serpentine superphosphate possesses certain advantages over superphosphate in respect of its physical condition and other practical features. These may be summarised as follows: (1) It is drier, and shows less tendency to “cake” than superphosphate. This means that it is usually more freely-running in the drill or topdresser. (2) As it is reverted and basic in character, it does much less damage to; bags than superphosphate. ' (3) It may be safely stored for long periods without material effect on its physical or chemical composition. (4) It is more pleasant to handle, especially when topdressing by hand.

(5) 1 Being a reverted phosphate, it is of a type which is becoming increasingly popular, and this is in line with modern developments in the fertiliser industry. An article in the “Journal” for February, 1941, by the Supervisor of Fertiliser Supplies (I. L. Elliott) discusses such developments. The two major advantages of reverted phosphates are:(a) They can be sown in contact with small seeds, such as turnips and swedes, without causing injury to germination. (b) On some soils plants may recover a greater proportion of the phosphates of reverted manures than is the case when . water-soluble phosphates are applied. Such soils are often termed “high-fixing,” for, they lock-up easily soluble phos- . phates in such a way that they are , not available to plants. ' When a water-soluble fertiliser is applied to such a soil, most of it is rendered unavailable, but the reverted phosphate dissolves much more slowly in the soil water, and although it is liable to be “fixed” when in solution, actively-growing plants will absorb a large proportion of the phosphate before this can take place. However, we still , have much to learn before

, the mechanism of “fixation” is fully understood. (6) If it is equivalent weight for weight to superphosphate (that is, if 3 cwt. of serpentine superphosphate gives as good results as 3 cwt. of superphosphate) a considerable saving in imported phosphate rock and sulphur is possible, for serpentine is a common mineral in several parts of New Zealand. l lt can be seen, therefore, tnat, should our investigation show the new mixture to be of equal merit to superphosphate on a weight basis, we have every reason to be satisfied with its performance. (7) Serpentine superphosphate should be at least as cheap or cheaper than superphosphate, when the manufacture of the material is on a sufficiently large -scale and is running smoothly. Some saving in the fertiliser subsidy should result, as there is every reason .to believe that ground serpentine can be produced at the works at a lower cost than superphosphate. The utilisation of a New Zealand product should also make possible a saving in sterling funds overseas. (8) Serpentine is a magnesium silicate, and magnesium is an element to which increasing, attention , is being paid. From work carried out by the Soil Survey Division and the Cawthron Institute, Nelson, it , would seem that quite a considerable number of soils ’in New Zealand are dangerously low in magnesium. Certain diseases .in apples and 'tobacco have been shown at Cawthron to be due to a - 'shortage of this element in the soil, and have been cured by the application of magnesium compounds. The value of the magnesium in serpentine superphosphate - is being .investigated, for this element appears to be present in a form readily available to plants. Serpentine also contains measurable amounts of cobalt, which is the element used in the control of “bush sickness” of sheep and cattle. : However, the amount of cobalt in serpentine super- - phosphate, although apparently available to plants, is very small, and is probably insufficient for the control of the stock diseases caused by a deficiency of the element. The value of the cobalt content of serpentine superphosphate is being investigated by the Animal Research Division, Department of Agriculture. 1 Disadvantages. (1) As it is a slow-acting fertiliser, it may not be as suitable for low rainfall districts as superphosphate. In

such, districts more soluble fertilisers tend to give greater responses. (2) Where the soil has a low “fixing” capacity, superphosphate is . usually held in the soil in a form available . to plants. To a considerable extent adequate liming overcomes the disadvantages of superphosphate on soils of medium “fixing” capacity, for the superphosphate reacts with the lime to form another type of reverted and available phosphate. : \ (3) Serpentine must not be regarded as a substitute for lime. For one thing, it is considerably less pure than reasonably good limestone, and contains fairly large amounts of useless materials. The amount of basic substances applied in serpentine superphosphate is small. Consequently, similar amounts of ground limestone should be applied where the mixture is used to those that would have been applied when using superphosphate. (4) Unless the mixture is as good as superphosphate on a weight basis, or unless there is some special merit in it apart from the production angle, serpentine superphosphate is merely a “diluted superphosphate” of lower

phosphate-content than superphosphate'. In this case, the extra costs of mixing and cartage confer no advantage.- There are probably some soils to which this applies, and on them the use of serpentine superphosphate would be uneconomic and undesirable. These areas have to be found by experiment. ■

Results of Fields Division Trials

■ The following trials with serpentine superphosphate have been' . laid down since 1939, and results from them are summarised below: 5 mowing trials on the effect of pasture topdressing. 160 observational topdressing trials on pasture. , ...■' , 12 potato manurial trials. , 9 wheat manurial trials. 1 oat manurial trial. 2 barley manurial trials. 46 manurial trials on turnips, swedes, rape, and chou moellier. ’ > 1 mangel manurial trial. . ' 1 maize manurial trial. 237: Total number of trials.

(1) Mowing Trials

Taking yields relative to superphosphate at 100, three trials at the Marton Experimental Area gave the following figures for serpentine superphosphate. Both manures were applied ,at 4 cwt. per acre. Trial P (700 days under trial), 100.0. Trial R (273 days under trial), 100.9. 1 Trial S (281 days under trial), 100.8. At Marton, serpentine superphosphate . gives almost exactly equal production to superphosphate when both manures are applied at the same rate. At Feilding Agricultural High School, the following results were- obtained. Here, a mixture of 3 cwt. of superphosphate plus 3 cwt. of lime was compared with serpentine superphosphate at 3 cwt. When yields of the former treatment are taken as 100, those of serpentine superphosphate (238 days under trial) on the same basis are 111.4. Moreover, serpentine superphosphate has consistently shown to advantage at Feilding. The trial at Ruakura Animal Research Station, Hamilton, was laid down a few months ago, and there are as yet insufficient results to summarise.

(2) Trials on Pasture

The maps which accompany this article are self-explanatory, and the salient results of observational topdressing trials on pasture are as follows. In . all cases the comparison is one of 3 cwt. of serpentine superphosphate per acre with 3 cwt. of superphosphate— that is, at equal rates. (a) In North Taranaki and on the Waihi plains serpentine superphosphate shows to advantage over superphosphate, and . because the lime response in these ' districts is not marked, it is usually better than superphosphate plus lime. Some soils in the Southland district may also come into this category. . (b) North of Auckland serpentine superphosphate on many soil types tends to give better results than superphosphate, but as the lime response is generally very marked here, it is evident that the new mixture can in no way replace adequate liming. (c) In several localities on the East Coast of the North Island, and in some parts of Canterbury, superphosphate gives better responses than serpentine superphosphate, probably because in

such areas highly-soluble fertilisers show to advantage. A similar effect is seen on some pumice soils, on which excellent results are usually obtained with superphosphate and good results with serpentine superphosphate. (d) Soils showing practically no responses to any fertilisers are located in Kaitaia in the far north and in the Waikato. In the former district many, soils have exceptionally high “fixing” power, and here even reverted phosphates are not effective. Liming plays a big part in the utilisation of many such soils. In . the Waikato most soils have considerable reserves of phosphate built up from many years of topdressing, and thus areas receiving no fertilisers deteriorate slowly. As a result, it may be one or two years before the effect of topdressing is seen. ' (e) Over most of the rest of New Zealand serpentine superphosphate

gives equivalent responses to superphosphate. r This group includes the majority of the trials.

(3) Potato Manurial Trials

The following table summarises the results obtained on a comparison of serpentine superphosphate with superphosphate with potato manurial trials.

In only one trial was the above difference statistically significant—in this case in favour of serpentine superphosphate. This trial was at Rangiora.

(4) Trials with Wheat

Oats and Barley Seven wheat manurial trials of a detailed layout were located in Canterbury and North Otago, and gave an average yield as follows: . ■ Bushels „ per acre Serpentine superphosphate lcwt. 37.5 Superphosphate lcwt .. .. 37.7 + Difference . . . . . . —0.2 . ' (not significant) Serpentine superphosphate 2cwt. 37.6 Superphosphate 2cwt. . . . . 38.4 Difference . . . . .. 0.8 ■ (not significant) A trial in the Turakina district yielded as is shown below, but the

results were not statistically examined. Serpentine superphosphate 2cwt. 22.6 Superphosphate 2cwt. . . . . 20.0 Difference . . . . . . —2.6 / Two barley manuring trials give the following yields: Bushels per acre. Southbridge Arrowtown trial. trial. Serpentine superphosphate 1 cwt. .... .. . 50.7 20.5 . Superphosphate 1 cwt. '.. ' 52.5 ' 19.3 Difference , .. .. I.S +1.2 Neither of the above differences are statistically significant. .An oat manurial trial was not harvested due to damage from wind and birds.

(5) Maize Trial Both superphosphate and serpentine superphosphate yielded 60 bushels of shelled maize per acre. (6) Mangel Trial This was not harvested due to caterpillar attack on the young plants. (7) Turnips, Swedes, Rape and Chou Moellier A comprehensive series of trials was carried out with turnips, swedes, rape, and chou moellier. As it is unwise to sow superphosphate with the seed of these plants, the comparisons have had to be widened to . include reverted superphosphate (that is, superphosphate reverted with lime), superphosphate, carbonate of lime mixtures, and proprietary manures. In addition, germination counts as well as yields have been estimated, as fertilisers with these crops have to be “safe” in this respect. In all cases both serpentine superphosphate and the manure with which it is compared are sown at the same rate per acre. Germination counts are given in the number of plants per 10 feet of drill length, and yields in tons per acre. Trials are of three types: “Type A” are detailed replicated trials; “Type B” are “half-drill strip” trials, which also give accurate comparisons; and “Type C” trials are simple trials where there are only a few plots of each fertiliser and statistical examination of the results is not possible. The following table summarises the average counts and yields from 46 trials. Positive differences indicate that serpentine superphosphate has given more plants or a better yield than the fertiliser with which ft is compared, and negative differences show the reverse. The numbers in brackets give the number of trials contributing to the average difference. Serpentine superphosphate is similar to, but no better than, a “reverted superphosphate” (that is, one reverted

with lime and with a ' minimum of water-soluble phosphate) The same conditions apply whether the superphosphate has been reverted at the works or by the farmer by mixing it with carbonate of lime. The trials have shown, however, that the latter mixture should be 1 part of lime to 1 part of superphosphate, and that the lime should be finely ground and the mixture allowed to “mature” for several days before sowing. Proprietary mixtures such as “Turnip Manures,” have proved unsatisfactory both in their effect on germination and on the yields resulting from treatment, and in these respects they are much inferior to. serpentine superphosphate. Farmers’ mixtures have given very variable results. Superphosphate has depressed germination, but the season was not sufficiently dry for this to be serious. A few trials, including a “no fertiliser” treatment, show a marked response to phosphates; all of these trials were in the Canterbury district.

Summary and Recommendations

(1) Present information indicates, that serpentine superphosphate should prove a useful fertiliser for pasture topdressing in the heavier rainfall districts of New Zealand. In North Taranaki, Waihi, and North Auckland, the new mixture is giving better results than superphosphate.

(2) Serpentine superphosphate has proved a safe reverted phosphate for sowing with the seed of turnips, swede, rape, chou moellier, and other crops liable to germination injury. (3) Serpentine superphosphate gives equivalent results to superphosphate on most of the common farm crops. (4) Superior physical . condition of the mixture makes it easier to sow, more pleasant to handle, safer to store, and less damaging to bags than superphosphate. (5) It is possible that the magnesium and cobalt-content of serpentine superphosphate may be valuable under certain conditions.

Acknowledgments

The investigation into the possibilities of serpentine superphosphate is' a truly co-operative effort, and is being carried out in collaboration with a number of officers of other Departments, whose assistance is gratefully acknowledged. The practical help afforded by the large number of farmers, members of Young Farmers’ Clubs, and pupils of District High Schools throughout the Dominion is providing information which will add to our knowledge of the value of this fertiliser. Future investigations aim to define more exactly those areas and crops on which serpentine superphosphate shows to advantage.

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Both Manures 1 applied at Number of Trials. Average difference: (Serpentine-super — Super) Total Yield of Tubers (tons per acre) 3 cwt. per acre - , 8 +0.2 . ' ■ 4 „ „ „ 1 +o.7 (significant) 6 „ „ „ ,4 —0.5 9 „ „ „ 1 > 0.3 (early potatoes) 12 „ „ „ 1 'i +1.3 18 „ „ „ 1 +1.2 Ave. difference — +0.2 +0.2

Treatment compared with serpentine superphosphate. Difference (Serpentine Super minus other fertiliser). Germination Counts. Yields in tons per acre. Type A 1 • I B ✓ c A 1 . ■ 1 B C 1 c Super : Carb, lime (1:1) Mixture +1.7(5) —1.6(3) . — —1.5(4) 1 1 —1.8(2) — Super: Carb, lime (3 : 1) Mixture — + 0.9(4) — — 1 +2.2(2)' — Reverted Super (all brands) —0.2(5) —1.1(4). +0.1(4) —0.9(4) | —0.1(3) +1.3(4) Proprietary Manures ++ • ' (all brands) — +6.1(9) +9.3(5) — 1 1 +6.6(6) +4.5(4) Farmers’ mixtures (all types) — +27.0(2) +4.1(1) — +8.4(2) —3.3(1) Superphosphate . . . . +1.6(1) - +1.8(2) —3.0(1) I —0.1(1) +1.3(3) No fertiliser . . . . —0.1(4) — — +9.4(3) 1 — — . — +9.4(3) . ■ -