August, 1909.] 



153 



Scientific Agriculture, 



surface. Ia the latter case, the dead 

 vegetation acts as a mulch, and prevents 

 evaporation of moisture. Not only la- 

 lang, bat also other weeds, more especi- 

 ally those presenting a large and flat 

 surface to the spray, were found to be 

 readily destroyed by the solution. 



The price of the chemical is the chief 

 item in the cost of the spraying work. 

 This price amounts to about did. per lb., 

 including freight. The solution can be 

 applied by means of any of the ordinary 

 sprayers on the market. 



In the Malay States the arsenite solu- 

 tion was used on land monopolized by 

 the lalaug grass and not applied to the 

 weed growing among cultivated crops. 

 The object was to clear the land in 

 a cheap aud efficient manner before 

 bringing it under cultivation, and the 

 maximum cost for freeing from weeds is 

 mentioned as about 2s, per acre, while 

 usually it does nob reach half this figure. 

 It will therefore be seen that this method 

 might best be adopted in clearing waste 

 land. 



Since the soda arsenite is so destructive 

 in its action, it is probable that it would 

 not be advisable to use it in spraying 

 weeds occurring in a cultivated crop, as 

 it appears more than likely that the lat- 

 ter would also be injured. In any case, 

 experiments should first be made on a 

 small scale. 



NEW SOURCES OF NITROGEN. 



(Prom the Gardeners' Chronicle, XLV., 

 1, 154, Feb. 6, 1909.) 



Since the investigations of Liebig, 

 Boussingault, Lawes and Gilbert, during 

 the first half of last century, into the 

 nature and sources of the elements neces- 

 sary for the nutrition of plants, the 

 great importance of an adequate supply 

 of nitrogen has become fully recognized 

 by all who are concerned with the culti- 

 vation of the land. Among plant-food 

 constituents nitrogen may be said to 

 take first place, being at once the most 

 costly, aud, under the ordinary con- 

 ditions which prevail in the garden or 

 on the farm, the most effective element 

 for increasing the yield of all kinds of 

 crops. Without the constant addition 

 of an abundant supply, either in the 

 form of organic material such as dung, 

 or as nitrate of soda or other chemical 

 fertilizer, the cultivation of field aud 

 garden produce rapidly becomes un- 

 profitable. 



All kinds of plants with the exception 

 of those belonging to the leguminous 

 class, take up the nitrogen which they 

 require from the soil in a combined state, 

 20 



almost entirely as a nitrate of lime, soda, 

 or some other base. Even before the 

 nitrogen in the farmyard manure and 

 other organic substances becomes avail- 

 able for the nutrition of crops, it is 

 changed into nitrates by the activity of 

 special soil bacteria. 



Unfortunately, from all cultivated land 

 there goes on a constant drain of this 

 element, and not more than 75 per cent, 

 of it added in manures is ever recovered 

 in the crops, evr n under the most favour- 

 able conditions. On account of the 

 soluble nature of nitrates they are 

 rapidly washed out of the soil into the 

 drainage-water, especially in winter, 

 when no plants are present to absorb 

 them, and a certain amount is decom- 

 posed with the formation of free nitrogen 

 gas, which escapes into the air and is 

 lost. Large amounts are removed in the 

 crops, and as these or the products 

 derived from them are transported into 

 towns and other areas away from the 

 land which produces them, it will be 

 readily understood that soils which have 

 been cultivated for centuries have been 

 undergoing a process of gradual exhaus- 

 tion of one of their most important 

 constituents. The demand f or supplies 

 of nitrates, which has increased to an 

 enormous extent both in the Old and 

 New Worlds during the last 30 or 40 

 years, becomes intelligible after con- 

 sideration of the points just mentioned, 

 and the spread of intensive methods of 

 cultivating the land is destined to in- 

 crease the demand. About 1830 nitrate 

 of soda was introduced from Chili and 

 Peru, and since that date it has tended 

 to stave off the nitrogeu famine and 

 keep up the crop returns. In 1860 it 

 was assumed that the deposits would 

 last for more than 1,500 years at the rate 

 at which the fertiliser was then being 

 used, but an increase of population and 

 a great extension of cultivated areas 

 along with iucreased intensive manage- 

 ment of the soil have falsified the 

 prediction. The world's markets are 

 now consuming 1| millions of tons of 

 nitrate of soda per annum, and the 

 exhaustion of the present source of 

 supply is well within sight ; a few 

 decades will see an end of it. Tem- 

 porary checks to the development of a 

 nitrogen famine have been made by the 

 addition of sulphate of ammonia to the 

 list of fertilisers supplying this all- 

 important ingredient, but no permanent 

 alteration in the growing need for it 

 could be expected from either of these 

 materials. 



That the food supply of the increasing 

 population is bound up with the dis- 

 covery of some new source of nitrogenous 

 plant-food has become more and more 



