RAIN AND PHOSPHATES.

Auckland Star, Volume XLIII, Issue 304, 20 December 1912, Page 9

RAIN AND PHOSPHATES.

DOES IT CARRY THEM DOWN? _ A series of experiments were recently mst-tuted in California with a view to ' ascertaining to what depth phosphatic ' fad. added in the form of phosphoric ' fertilisers, is carried by the rain into the 1 ranous soils. The experiments were ' aade primarily for the purpose of findmg out whether these manures, when ( added in the orchard, are carried down ' to tn e roots of the trees, and, though ; ™ experiments are not yet complete,' ' the results so far will be "of interest to J ! farmers and orchardists in New Zealand. ' According to Professor Loughbridge, C *ho conducted the experiments, the re- , suite are emphatic, and show that, except in very sandy soil, the phosphoric foddoes not re_ch the roots of trees, _ oat is retained in the upper few inches, Wen in the presence of a heavy rain- _ *»•• I sing a high grade superphos- , paate carrying 17 per cent, of soluble t FlOsp-horic acid, it was found that heavy f pky soils would retain 10001b per acre t ™ tte upper Sin, that a loam soil would j ( "old that amount in 6in, while a sandy a •w would allow it to pass quite deep. - & adds that he was struck by this t locking-up" of phosphoric acid at the 9 •""Me in the examination of the soil of \\ ** orange orchard where liberal appli*«o_! of phosphates had been made for g ™W_ Te-irs. The examination of the _ *P (ilack day) showed that the a Wa«W»t of phosphoric acid in the upper »- Was .30 per cent., while in the next ™» &_d still deeper, the percentage was ®y, .OS. Evidently the upper Gin had _ all t_» phosphate that had been b **■*- In many years. \ (

SOIL ANALYSIS. ITS P__CTICAL VALUE. From time to time we receive innniriea from farmers in various parts of the Dominion in regard to the analysis of soils and m many cases the idea appears to be entertained that having a soil analysed is a ready means of determining its manuriaJ requirements or of obtaining an indication of its fertility. We have always held that soil analysis is of little practical assistance on these points to the New Zealand farmer, and an article in a recent number of the British Board of Agriculture's Journal supports this view. Take first the broad question: To what extent does an analysis of a sod give an indication of that sods fertility? The fertility of a sod may be defined as its power of growing crops, and it is obinous that, while this depends to a great extent on the soil's ability to supply the crop with what is often termed piant food—in particular, nitrogen, phosphate, and potash—in a suitable form, this is by no means the only essential condition. A sufficient and continuous supply of water to the roots, and proper aeration of the soil, are quite as necessary for satisfactory growth as the supply of manurial ingredients. To a very great extent these factors are regulated by circumstances of climate, exposure, drainage, and depth of soil, which obviously cannot be determined in the laboratory. Even if the analyst could give complete information about the plant food, and were able to measure accurately the mechenical condition (Le., texture) of the soil, and to correlate it exactly with the questions of aeration, drainage, and water supply, the information obtained in the laboratory could only give a very incomplete idea as to the fertility I of any particular field, and the farmer J "vould have to supplement it by his local j knowledge, experience, and judgment. Unfortunately, however, the analyst : cannot at presen* give more than very rough and incomplete information even ! about those factors influencing fertdity ' which lie within his province. Some of the difficulties with which he has to con- ' tend may be mentioned here. He can ; determine as accurately as need be the : total amounts of nitrogen, phosphates, '• and potash in the soil, but it has been ! found that, even where external factors j such as climate, depth of soil, etc, do not I enter into the case, there is often little ! or no connection between these amounts I and the soil's fertility or its manurial requirements. Any ordinary soil contains much more total plant food of all forms than a single crop of any kind can possibly require. Most of this plant food, however, is in an unavailable or lockedup condition, and is only gradually set free or made available, the rate varying in different cases. As the plant can only make use of the free or available food, it is easy to see that it is quite possible for oae soil, containing quite small amounts of the manurial substances, to produce better crops than another soil containing large quantities, if for any reason the first soil gives up its material to the plant at a more rapid rate than the second. In fact, many i sods contain very large quantities of, say, . phosphates, and still respond most readily ! to small dressings of manures containing ', available phosphate, because practically i all that is already in the soil is unavailable, and, as far as the plant is concerned. ' might almost as well not be there at all. (It may be remarked that exposure to air and weather, and treatment which secures a healthy condition of soil, are ' some of the factors which determine the rate at which plant food becomes available in the soil, so that, apart from their . other important functions, good cultiva- ! tion, draining, and liming may partly take j the place of manuring in a soil which j contains large stores of locked-up food.) | In the case of phosphates and potash, | a method has been devised of roughly j measuring the amount which may be re- ' garded as of immediate or prospective value to the plant, by finding, not the total amount of phosphate or potash j present, but the amount which is dis- ! solved out in a given time by a weak I solution of citric acid. This method gives | results which in many cases indicate fair- j ly well whether a particular soil will respond to applications of cither of the I two kinds of manure, and may De used j in oomparing soils of the same class. At the same time there are many cases where the results obtained are at vari- ; ance with those obtained by actual ex- ' periment in the field. So far, no ready i method has been discovered by which the availability of the nitrogen in the soil can be estimated except as regards the small amount present in the form of nitrates or of ammonium salts. | As already mentioned, two conditions essential for the satisfactory growth of crops are a sufficient supply of water and the proper aeration of the soil. To a great extent the ability of the sod to meet the plant's requirements in these respects is determined by the size and nature of the particles of which the soil is composed. By carrying out a "mechanical analysis,"' the proportions of particles of different degrees of coarseness can be measured, and as the results of such analyses accumulate, it will probably become possible to estimate from such an analysis such factors as waterretaining power, ease of drainage, ability to withstand prolonged drought, and so forth, and even to say with some de--free of certainty what systems of cultivation are most likely to result in a good tilth at any particular time of year. At present, however, such an anaysis is tedi3us and expensive, and in most cases an experienced farmer would be able to rain more useful and accurate information )V walking over the land and examining t carefully at different times of the year, i On the whole, in the present state of I >ur knowledge, it must be concluded (1) j ■hat chemical and mechanical analyses of .oils are of little practical value except n a few special cases; (2) that an inteligent and experienced local farmer could rive a much better idea of the fertility • if any particular farm or field than an ■ nalvst; and (3) that as a means of de- ( erminating the manurial requi-ements of ' soil a simple field experiment gives more J ccurate and reliable knowledge than or- 1 mary analyses. , 1 In certain special cases, however, soil t nalyses may undoubtedly be of great i iractieal value, e.g., (I Iby a very simple < est, which most farmers could carry out £ or themselves, it is possible to say whe- \ ber a soil is in need of liming or not; . 2) if, by means of a soil survey, such j s those now being carried out in many £ arts of the country, complete informaion has been obtained with regard to . rime special class of soil occurring in a . mited area different samples of that particular soil can be compared and classi- T ed fairly accurately, and their manurial nd cultural requirements predicted with considerable degree of certainty. j ■ I!