CHARACTERISTICS OF SERPENTINE SUPER

New Zealand Journal of Agriculture, Volume 66, Issue 1, 15 January 1943, Page 11

CHARACTERISTICS OF SERPENTINE SUPER

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G. H. HOLFORD,

Supervisor of Serpentine Development, { Wellington.

1 —mi—mi—mi—mi——mi—mi—mi—mi—mi—mi—i jk i * I This article outlines the I | chemical and physical charac- J 1 teristics of serpentine super- | j phosphate, and its practical | j value as a fertiliser in terms of T | practical farming. | •£©11—Illi—Illi—Illi—Illi—Illi—Illi—Illi—Illi—•Illi—Illi—Illi

IN view of certain criticisms levelled at the use of serpentine with .superphosphate, it may be mentioned at once what serpentine super is not. For instance, it is definitely not merely ordinary superphosphate diluted with a soft rock, added as a “make-weight” and thereby involving uneconomic use of labour and transport. When properly ground and mixed with super, under suitable conditions, serpentine imparts to super important -desirable chemical and physical properties, and adds as well, essential plant nutrients to those already contained in straight super. This means that speaking generally, - serpentine super is a more efficient fertiliser, weight for weight than normal superphosphate, and, as Mr. Cockayne has

stated, it increases the effective fertiliser ration of the farmers by 33J per cent., so playing an important role in increased farm production, an essential part of the Dominion’s war effort. What is Serpentine ' Serpentine is a mineral containing mostly magnesia and silica, as well as certain important trace elements, . some of these likely to be of possible value in plant and animal nutrition. Of these, cobalt is of special interest. Serpentine is found in abundance in New Zealand, but unfortunately not in deposits alongside the railway. This largely accounts for its higher cost per ton than lime, so many deposits of which are adjacent to rail. Incidentally, the name serpentine is given this

mineral because the rock often has the appearance of a snake’s skin, being of a . mottled greeny blue colour.

Manufacture

The serpentine rock is ground to a fine powder at the superphosphate works, and one part by weight of this material is mixed with three parts of hot moist superphosphate and the mixture allowed to chemically react and mature in piles. . Only slight setting takes place, and, after the serpentine super is dressed and bagged, it remains thereafter in a free running condition. The main features of the chemical reaction are that the water soluble phosphoric acid in the super is changed ; mainly into a magnesium phosphate, a “reverted” type of phosphate, by the magnesia in the serpentine. Some magnesia also becomes water soluble and is available for plant use. The silica portion of the serpentine becomes colloidal silica. There is an increase in availability of some of the other elements contained in small amounts in serpentine, i.e., iron. The net result of the chemical reactions is that serpentine super, unlike ordinary super, is, a non-acid fertiliser, the magnesia of the serpentine acting in this, connection as does lime. . It may be . mentioned that it requires several hundredweights of lime in the soil to neutralise the acid condition of one ton of ordinary super, and this is one of the main reasons why liming is so important, especially on acid soil types where superphosphate is applied.

Use of Lime

Whilst in the use of the serpentine super, there is no drain on the lime in the soil to neutralise acid in this fertiliser, it must not be taken that the use of serpentine super will obviate the use of lime. On acid soils the use of lime is still necessary, but in areas so distant from rail or lime supplies as to make its application impossible, the use of a neutral fertiliser such as serpentine super is advantageous. It means too, that there is no chemical injury to bags, a common fault with superphosphate, and in these days of bag scarcity and with higher priced bags, this is quite an important feature of this new fertiliser. . Again, the mixture does not cake or set hard as does super so the laborious job' of breaking up lumps prior to sowing the fertiliser is obviated. Farmers find that serpentine super is easy, to sow, either by drill or by hand. The physical attributes of this new fertiliser will be at once obvious to all farmers. The chemical properties, as indicated in crop or pasture growth can only be appreciated after its use. Chemical Properties As already mentioned, the magnesia in serpentine (there is approximately 35 per cent.) reacts with the water soluble phosphoric acid in super to make

a magnesium phosphate. Scientific research has demonstrated that this is a

particularly useful type of phosphate for farm use. It is what is called a “reverted” phosphate, and this type is less liable to be “fixed” or “locked up” by certain soil chemicals with the beneficial result that more of the applied, reverted phosphate is available for growing plants, and in turn more goes to the animals or humans consuming such plants than is the case with super- - pnospnaie. The whole question of soil phosphate fixation is a complicated chemical problem which it would take many pages

to discuss, but, in essence, it, is this. When water soluble phosphoric acid,, as in super, is applied to the soil, it combines with some base or bases in the soil. These bases from the standpoint of phosphate recovery by plants may be good or bad. In the good category are calcium and magnesium; in the bad, iron and alumina. Discussing the bad bases first. Iron and alumina phosphates,' formed by the combination of iron and alumina with water soluble phosphoric acid, are very little, if at all, available for growing plants. So it is said that iron and alumina “fix” or “lock up” the phosphates. ■

. On the other hand, when the water soluble phosphoric acid combines with calcium ’ or magnesium in the soils, plants can much more readily secure their phosphate needs from either calcium or magnesium phosphate than from the iron and alumina phosphates. Further, the recovery from magnesium phosphate is, according to overseas authorities, better than from calcium phosphate. Now, iron and alumina are most active in acid soils, so, when lime is applied, some of their phosphate fixing powers are lessened. This is one of the most important functions of liming soils and of particular value where super is the phosphatic fertiliser used. When water soluble phosphoric acid is applied to soil, it can therefore combine with one or more of the good or the bad bases, and over large areas of New Zealand, our soils contain a good proportion of the undesirable bases iron and alumina.

In order therefore to ensure that the form of phosphate applied is of the most desirable type, it is reasonable to suggest that it is worth while to add a good base to the phosphoric acid before this is applied to the soil. This is just what is done by adding serpentine to super at the fertiliser works. The phosphoric acid is “reverted” with magnesia and this greatly minimises it being “perverted” by iron and alumina in the soil. Of course, lime can be used also to revert the phosphate but it is considered ' better to use serpentine rather than lime in the works, applying lime as such in suitable quantities, depending on soil and other conditions. Magnesia as a Plant Nutrient As mentioned, some of the magnesia of the serpentine becomes water soluble and so is available as a plant food. Our New Zealand soil surveys are now indicating that over wide areas the magnesium content of the soil is getting low, possibly dangerously so in some areas. It should be realised that magnesium is a base that leaches out of soils, and is utilised by plants and animals much like calcium, and that up ; to the time of using serpentine super, very little magnesia had been applied in artificial manures . to our soils. Magnesia is a very important nutrient for plants and animals, and time may show that one of the most important attributes of serpentine super is its water-soluble magnesium content.

Fortunately, the silica content of serpentine is . inh a form that allows a chemical .reaction with super to the end that colloidal silica is formed. The presence of colloidal silica, in serpen-

tine super further helps the uptake of phosphate by plants, and so enhances , the fertiliser value of this material. 1 “Trace” Elements As well as magnesia and silica, serpentine contains small percentages of what are called “trace” elements, some of which have a possible value in plant and animal nutrition. Cobalt, nickel, iron, zinc, manganese occur in serpentine. - Cobalt is the important mineral for “bush sick” areas, but there is not sufficient in the usual per acre dressings of serpentine super to enable the fertiliser to supply a sufficient dressing of cobalt, as is the case with cobaltised serpentine super. However, the repeated annual dressings of even small quantities of desirable “trace” elements are likely in time to have some value. This point also may be made. The chemical analyses of serpentine super somewhat approximates that of a mixture half and half of superphosphate and basic slag, and observations of pasture experiments suggests that the field results of serpentine super and the super-slag mixtures have much in common. Time alone will determine whether these preliminary observations are borne out over several years’ trials. . If they do, grassland farmers in the wetter area of New Zealand will have a fertiliser equalling one which experiments and experience have

shown in the past to be „ excellent, i.e., super. . and slag, half , and half. , “ ! It may be pointed out, too, that as each farmer receives his fertiliser quota, he should appreciate the fact that this is one-third greater because of the advent of serpentine super; a very important consideration when his ration is about one-third of his requirements'some two year's ago. Whilst all the evidence points to serpentine super being a first-class fertiliser, it is of necessity, now bfeing applied at rates much less per acre than' in pre-ration years, and, in any comparison of results under present conditions with these when several times the amount of fertiliser was applied per acre, this should be borne in mind. In concluding . this section on the chemical aspects of serpentine super, it will be realised by farmers that the addition of serpentine to super in the approved manner gives the new mixture a character tending . definitely to increase its fertiliser value when used in crops and pastures over wide areas of this Dominion. This also, is associated .with very desirable physical properties, no rotting of bags and no setting of the fertiliser in the bags. ■ ■ ■ ■ In a large number of official trials carried out by the Department of Agri-, culture over the past three years, it has been shown that when soils have been asked y the question, “How good is serpentine super compared with super

or reverted super, or super and lime?” a favourable answer has been obtained. Generally speaking, 1 cwt. of serpentine super is at least as efficient as 1 cwt. of straight super, and on many areas it is better, and this, fortunately, where fertilisers are needed most. As a fertiliser for farm crops, it has given good results and on cruciferous crops, turnips, swedes and rape, serpentine super not only gives good crop yields but there is no germination injury as is the case with straight super. So on crops and on grassland serpentine super can be used with confidence by New Zealand farmers.-

Careless Handling of Pigs

Concern is felt in many quarters at the prevalence of bruises and weals on various parts of the skin of pigs. Farmers, dealers and carriers should do their utmost to avoid causing skin blemishes, which may bring about the degrading of otherwise prime , porker or baconer carcasses. Much can be done by a little more care and patience, the use of a proper yard and loading race, and the absolute prohibition of rough handling, stock whips and sticks. • All engaged in the handling of pigs should obtain a copy of the Department’s free bulletin (No. 175) on this subject. ,