Vol. XIII. Xo. 32;^. 



THE AGRICULTUEAL XEWS. 



291 



MANURES AND MANURING. 



THE SUPPLY OF POTASH. 



The cf.>.satiuii ol txprnts from tin- Stas^t'urt .Miiit-s in 

 Gennany, which constitute the priiicijial and practically tlic 

 only source of ordinary potasli manures, raises the cinestion 

 as to what substitutes can be enijiloyeil in the near future, 

 and from what quarters these can be obtained. 



Frir many years a consideralile amount of work has been 

 done in the I'nited States and elsewhere with a view to 

 rendering available the potash which is contained in certain 

 well-known and widely distributed varieties (e.g. orthoclase) 

 of the rainend called felsjiar. It will be reniemliered that 

 this substance is a common constituent of many soils as well 

 as occurring in vast (juantities in certain rocks like granite. 

 Trials have shown that it is not a paying operation to manu- 

 facture available potash fi-om felspar for the sake of the 

 I)otash alone. The discovery, however, that Portland cement 

 can be obtained by the treatment of felspar with lime as well 

 as available jKitash as a by-product, has of recent years 

 rendered the idea pi-Actical>le and indeed, several factories 

 liave been established for carying out these operations. At 

 the same time the unit price of potash from this artificial 

 source is gi-eater than that of the mineral obtaineil from 

 natural mines, and u]) to the pre.sent this artificial supply has 

 been altogether inconsiderable. There is reason to .suppose 

 now, however, that, owing to the complete cessation of the 

 (ierman supply which, as already intimated, ha.s held a world 

 mono|)oh-, some possibility e.xi.sts that a ri.se in price may 

 render the artifical production of potash fertilizers feasible, 

 —a circumstance of importance to those who are 

 engaged in the production of certain crops. 



Another alternative in the present situation might be to 

 take advantage of the Indian su[)ply of saltpetre (potassium 

 nitrate). In 1906-7, India cvixirted piincipally by way of Ben- 

 gal, .■?.'):?,378 cwt. of nitrate of potash, valued at Ks. 4,l.")l',.'>-" 

 (£l'7(>.1()M). The largest quantities of this amount were 

 distributed in order of nomination to the United States, 

 I'nited Kingdom, China (Hong-Kong) and Mauritius. The 

 a\erage value pel- hundredweight of Indian nitrate of potash 

 for the five jears preceding 1907 was 14-5s. 



In connexion with the information just given it may be 

 of interest to add a few words on the chemistry of nitrate of 

 potash. It is olitained in India in the form of an efflores- 

 cence at the surface of the soil, and the conditions 

 for the formation of the .salt are liriefly as follows: 

 Supplies of nitrogenous organic matter; climatic condi- 

 tions favourable to the growth and action of nitrifying 

 bacteria which convert urea and anunonia successively into 

 nitrous and nitric acifl: the presence of potash: and meteoro- 

 logical conditions suitable for the efflorescence of the 

 jiotassinm nitrate at the surface. This necessary coniliina- 

 tion f)f characters is to be found in a marked degree in 

 various districts in the Indo-Gangetic tract. 



It is well known that nitrate of potash has an important 

 Use in the manufacture rif explosives, and it is a further 

 point to anticipate nhether the Indian Government has not 

 already prohibited the exportation of nitrate of potash under 

 the category of contraliand of war, in which case it would 

 .seem that agriculturists will have to look to either artificial 

 mineral supplies as dealt with in the first paragraph of this 

 article, or rely upon the i^ractice of carefullj- returning plant 

 debris and wood ashes to the soil, t'areful attention to this 

 latter procedure should ensure adequately all neeessary 

 demands for jxitash. It may be noted, however, that there 

 are one «■ two by-products of tropical crops in existence 

 which are very rich in potash and maj- possibly come inti) 



use as an organic-potash manure, for example, Senat seed 

 from the Soudan, the ash of the husks of which is rich in 

 nutrients containing as nnich as 42 per cent, of potasli (K._,0). 

 Material of this kind as well as sea-weed (also rich in potash) 

 sliould jirove very valuable. 



Nitrate of potash is not used largely as a manure as it is 

 rather expensive. For sugar-cane in Barliados, however, and in 

 other islands where the soil has to he kept rich in available 

 plant food, nitrate of potash has proved useful and possibly 

 economical because nitrogen l>eing required as well as potash, 

 the planter has in this manure two essential elements in 

 a readily available form. Owing to the richness of nitrate of 

 jwtash, its jjurity and complete availability, it is necessary to 

 use only small quantities per acre, for example J-cwt.. which 

 is significant as regards freight. 



The usual guarantee for nitrate of potash is 17 per cent, 

 nitrogen and 40 per cent, of potash, the unit prices for which 

 are quoted at 14.s. 6rf. and .3s. 9i/., respectively. 



GROUND LIMESTONE. 



AVhen discussing the sulject of liming, confused ideas 

 are oi-casionally met with in regard to the question of 

 limestone versus slaked lime or quicklime. Perusal of an 

 article in the Journal of Af/riculture, of Xew Zealand 

 (Ai)ril 20, 1914), will show that all the good effects resulting 

 from the employment of quick or slaked lime on the soil 

 may lie produced with greater safety by ground limestone. 

 The etiective nature of ground limestone naturally depends to- 

 a large extend upon its mechanical condition: the finer the 

 crushing the better the results. Chemically, limestone, like 

 lime, is alkaline, and tends to destroy the stickj- nature 

 of soils. It further supplies a base for the formation of 

 nitr.ites in the soil and liberates potash from the insoluV'le 

 soil silicates and prevents j)otash fertilizers from passing into^ 

 an unavailable condition. Limestone furthermore has 

 a favouralile infiuencc on the availaV>ility of phosphate^ in 

 the soil. 



In the article referred to, mention is made of the fact 

 that material containing limestone may also contain a high 

 percentage of clay or other so-called impurities. It is quite 

 possible that under some conditions these impurities are an 

 advantage, as for instance, when limestone is to be added t« 

 light soil. As regards the amount that should be applied per 

 acre, experimental work in England and America indicates 

 the reversion to the old-time custom of applying limestone in 

 large rather than in small cjuantities at a time — by the ton 

 rather than by the hundredweight. Two tons of limestone 

 per acre is said to be the smallest amount that should lie tried 

 on an experimental scale at first. It may be nrited here that 

 in the case of very tenacious claj's, it may be found advisable 

 to begin with a dressing of quicklime because the action of 

 this substance is more active than that of limestone. 



There is a call in Xew Zealand for more experiments 

 with lime: it is suggested that demonstratio}i plots should 

 be laid down to show the relative eflicienc^' of ground lime- 

 stone of varying grades of fineness, and therefore of varying 

 cost; to show the eftect of varying quantities: varying methods 

 of application: caustic lime in varying forms: the effects of 

 these in combination with phosphates on various crops, and 

 so on. In these as in all other manurial experiments, a number 

 of years will be required before really decisive conclusions can. 

 be drawn as to the beneficial effects derived under the various 

 conditions. 



It may be added that in the West Indies also similar 

 experiments are wanted, and in coimexion with this require- 

 ment the reader is referred to an article that appeared 

 recently in the Agricultural News, Vol. XIII, p. 226. 



