The Pamphlet Collection of Sir Robert Stout: Volume 72
On Manures and the Manure Act
On Manures and the Manure Act.
The fertility of any soil depends on two main conditions: (1) the composition and physical properties of the soil itself, and (2) on the surrounding conditions as regards climate, viz., temperature, rainfall, &c. The latent resources of a soil as concerns plant food, when climatic conditions are favourable, depend on the previous treatment it has received as to the removal or otherwise of the vegetable products grown on it. When nothing is removed and the products return again to the soil, the degree of fertility may be retained, or even gradually increased. In new countries, like New Zealand, soils possess the accumulated fertility of ages, and that such does exist in our own case is shown by even the few investigations that have been made with regard to the composition of the soils here.
Thus, taking the most important soil constituent, nitrogen, and comparing the amount present with that contained in the soils of Great Britain, as shown by Messrs Lawes and Gilbert, this is at once rendered evident. The same indication is shewn to a greater extent by results obtained by these investigators with the United States and Canadian virgin prairie soils. Comparing these results, we find that in Great Britain the amount of nitrogen present to be. 156 per cent; (mean of 19 analysis); in New Zealand, 273 per cent (mean of 13 analysis); and in the United States virgin prairie soils 320 per cent (mean of 11 analysis).
The presence of this accumulated fertility explains probably the cause of our being able to grow grain so frequently and to such perfection here. When, however, the products of vegetation are removed from the immediate vicinity of the soil, if it is desired that the degree of fertility should be maintained it is necessary that some restoration should be made. This is done to a certain extent by the natural decomposing agencies at work in the soil by which the reserve store of unavailable plant food is gradually rendered available; but under our present system of agricultural practice, the process is not sufficiently rapid to retain the normal fertility of the soil. Exhaustion is also retarded by a judicious rotation of crops, but sooner or later a direct application of plant food in the shape of manure becomes necessary to restore the balance of fertility.page 18
But, fortunately, it is found that the exhaustion of soils is not of a complete, but only of a partial nature. The illustrious Liebig enunciated a law which is now known as Liebig's Law of Minimum, which states "that every field contains a maximum of one or several, and a minimum of one or several nutritive substances. It is by the minimum that the crops are governed, be it lime, potash, nitrogen, phosphoric acid, magnesia, or any other mineral constituent."
As by strengthening the weakest link of a chain we increase its whole strength, so it is by augmenting the constituent in a soil that is most deficient in an available condition, that we increase the strength or fertility of a soil. Science associated with practice has done much to assist in this matter. It has been found that the main constituents most deficient in soils, and which produce when added increased growth, providing other conditions are favourable, are nitrogen, phosphoric acid, and to a less degree potash. These are the main constituents of all the more important manures.
It has also been found that our ordinary crops have special requirements with regard to these three constituents. That grain crops and grasses are best assisted by the application of nitrogenous manures, root crops by manures containing phosphoric acid, and leguminous plants such as peas, beans, cloves, &c., by potash manures. The action of these substances is not always of a direct nature in augmenting the quantity of such within the plant, for, strange to say, there is less nitrogen removed in the produce of a grain crop than in that of a root crop, and no more phosphoric acid in the root crop than in the grain crop. Phosphoric acid applied to the root crops, and potash to leguminous crops enable them to assimilate more nitrogen, yet the direct addition of nitrogenous manure to these is not always beneficial, but sometimes even prejudicial as far as the agricultural value of the crop is concerned. The condition in which the food constituents exist in the soil, determines their assimilation by plants, the most suitable form being that in which they are either soluble in water or in the root juices of the plant. The mechanical condition of both soil and manure as regards the subdivision of the particles, aids in the assimilation of plant food to a considerable degree.
General manures, like farmyard manure, seaweed, &c., in which all the necessary plant food constituents are more or less present, are applicable only to a limited extent in New Zealand. Special manures are better suited to our requirements, and where rotations are carried out, the manuring of the turnip crop with superphosphate of lime is often found sufficient for the course.page 19
Land in good condition contains a considerable quantity of available plant food, and by a little assistance with special manures containing the food constituent most required, the crop may be grown many years in succession. Many examples of this are shown by the classical experiments of Messrs. Lawes and Gilbert, at Rothamstead, extending over a period of 50 years.
The advantages derived from the practice of applying special manures of the nature best suited to the crop, as shown by practical as well as scientific experience, is of extreme importance. Not a few cases are known where manures have been applied to crops for which they were quite unsuited. This, hitherto, has not been always the fault of the farmer, but often of the manufacturer. Thus, at the present time, manures are being offered for sale in New Zealand as turnip manures, which contain a high percentage of nitrogen, and but a trace of soluble phosphate. These are excellent manures of their kind, and are also cheap, but not the sort of manure that the turnip crop requires. It has been found both here and in England that an excess of nitrogen in a turnip manure tends to produce too much leaf development at the expense of the bulb, and also at the same time lowers the feeding value of the latter. The best manure for turnips is a soluble form of phosphate of lime, such as we have in superphosphate, with but a small quantity of nitrogen. Our meat freezing industry has given us a cheap form of nitrogen in dried blood, animal guano, &c., that should produce good results on our wheat and oat crops, and grass land, but whether it will pay to use them at the present low price of grain, or whether our soils in their present condition will return sufficient compensation for the outlay, is a matter that needs further consideration. These manures as at present put on the market are more of the character of general manures, since they contain nitrogen, phosphoric acid, and a little potash; they are better suited for the purposes of the market gardener, or for the growth of green corn feed, rape, &c., where a good leaf developement is required, than for application as special manures.
Failure of manures to produce the desired effect is not always due to the manure itself. Local conditions as to climate, rainfall, &c., are often sufficient to destroy the beneficial action of a manure. At the same time the conditions may be such as to render one form of a manure more suited to the requirements of a district than another. A case in point is shown by the preference given in the lower part of page 20 the Middle Island to the use of phosphatic guanos, such as the Coral Queen, Chesterfield, &c., for turnips, whereas in Canterbury superphosphate is found to give by far the best result. Local experience is of considerable value, and the establishment of experimental stations in New Zealand, where comparative experiments could be made with respect to the use of manures, the growth of new crops, &c., would be of material assistance to the farming community. In the United States there are at the present time fifty-four such stations, each publishing its own record of work in the form of bulletins or reports, which are distributed free of cost to any farmer who cares to apply for them. At many of these, also, the work of analysing and controlling the quality of manures sold in the State is carried out.
An insight into the quality of the manures obtainable in this country may be obtained from a report published by the School of Agriculture in 1891. With a few exceptions both local and imported manures appear to be of good quality, and but little evidence is forthcoming as to adulteration, and even the few cases met with were probably the result of want of knowledge on the part of the manufacturers.
The manure act passed by Parliament in 1892 will have the effect of not only keeping adulteration in check, but also will enable the agriculturist to purchase the manure best suited to his purpose. At the same time, owing to a provision made in the act by which the manufacturer or vendor is required to publish the value of the units (each 1 per cent per ton) of the more important constituents in the manure, the farmer is able to judge as to the cheapest source from whence to purchase his manure. This will also have the effect of inducing a healthy competition between the manufacturers.
The Manure Adulteration Act 1892, provides that the seller of any manure shall give to the purchaser of any quantity not less than 10cwt. at the time of purchase or delivery a signed invoice certificate, such certificate to state the percentage of the more important constituents contained in the manure, and also the value placed of each unit of such constituents by the seller. It is necessary that each package of the manure shall be branded with the trade mark, or its equivalent, of the seller. The seller failing to deliver such certificate, or omitting to brand each package, is liable for the first offence to a penalty of not more than £10 and not less than £61, and on a second conviction to a penalty not exceeding £25. Analysts have been page 21 appointed under the act to whom samples may be sent for analysis, which must be done within 14 days after delivery and before the bulk is broken. The vendor is to be notified when the manure is intended for analysis, and shall receive an offer to have the samples divided in his presence into five parts, each part to be marked and sealed, two parts to be delivered to the vendor, two parts to be retained by the purchaser, and the fifth part to be submitted to the analyst. The vendor may also forward one part to any analyst, and should the results obtained differ from those of the purchaser's analyst, the then one or both of the remaining parts shall be forwarded to the analyst of the School of Agriculture, Lincoln, for analysis, the mean of the three results to be accepted. The form of the certificate of the analyst is set forth which is to state the particulars in which the results obtained differ from those stated in the invoice certificate. A copy of the certificate is to be forwarded to the vendor. The certificate is also to state the value of the manure on the basis of the value per unit per ton published by the vendor. Any difference between such total value and the price charged for the manure to be allowed by the vendor. Should the deficiency exceed the following limits:—Phosphates (soluble and insoluble) 3 per cent, potash 1 per cent, nitrogen 1 per cent, the deficiency is to be allowed by the vendor at double the above rates, until they reach the following limits:—Phosphates 6 per cent, potash 2 per cent, and nitrogen per cent. Should the difference exceed these amounts, the vendor is liable on conviction before a resident magistrate, for the first offence to a penalty not exceeding £20 and not less than £2, and for a second offence to a penalty not exceeding £50 and not less than £5. County Councils may be authorised by the Colonial Secretary to appoint inspectors, who may be directed to obtain samples from any manure offered for sale within the county, and to submit them to an analyst for analysis. Refusal to sell to an inspector renders the person offering the manure for sale liable to a penalty not exceeding £10 and not less than £1.
The act has only been in force about 14 months, and it is too early yet to judge of its utility, but there can be no doubt that it is to the interest of farmers to take advantage of it, if only for the purpose of getting good value for their money. But it should do more than this, it should be utilised for the purpose of selecting such manures in the market as are best suited for the crops it is intended to cultivate. Good results can only be obtained when the manure is of the right page 22 kind and properly applied. There is often a considerable difference between the agricultural and the commercial value of a manure. The former can only be ascertained by observing the increased yield of crop due to the manure. This increase, multiplied by the market price of the product, and divided by the quantity of manure applied will give the agricultural value. An example will make this clear. Supposing an acre of wheat is manured at the rate of 2 cwt per acre, the price of the manure being 5s. per cwt, and taking the increased yield as 8 bushels per acre, which at 2s. 6d. per bushel will be £1, then the agricultural value of the manure will be 8 × 2s. 6d.÷2=10s. per cwt., showing a profit of 50 per cent, on the commercial value of the manure. The farmer himself only can ascertain the agricultural value of a manure, and often a simple field experiment, showing the difference between the produce of a manured and an unmanured plot, will teach a lesson that can be learned in no other way.