27 



in supplying any plant-food. It is best to apply it with other manures, 

 and is valuable for root-crops, and may even sometimes be used instead 

 of potash manures. Like the latter, it has a bad effect on clay soils. 



Eight-plot Test. — In order to ascertain accurately the effect of 

 different manures on a particular soil, experiments with plots should 

 be carried out, although the manures required can be roughly estimated 

 by an analysis of the soil. As great accuracy as possible must be 

 aimed at, as errors always creep in, however carefully the experiment 

 is conducted, and unless the results show a difference of lo per cent, in 

 the yield of crop no accurate conclusions can be drawn. In choosing 

 sites for the plots, uniformity in the nature and aspect of the soil 

 must be strictly maintained, also in the size and shape of the plots, 

 and the questions of previous manuring and cropping must be con- 

 sidered. A convenient size for the plots is about ^ of an acre or more, 

 and small plots of a few square yards are of Uttle use in obtaining 

 accurate conclusions, as the great care needed for the experiments on 

 small plots counterbcdances the effect of the manures on insect pests 

 and fungi. The land must be measured out, and the manures weighed, 

 and properly mixed and applied, about a week before sowing the seed. 

 If possible, the plots should be laid out side by side, the munber 

 being eight in all. The choice among the fertilizers to be used should 

 lie between {a) nitrate of soda and sulphate of ammonia, (6) super- 

 phosphate and basic slag, and (c) kainit and sulphate of potash, one 

 of each being used, and the crop, of course, being the same on all the 

 plots. On No. I plot apply nothing, on No. 2 nitrate of soda, on No. 3 

 superphosphate, on No. 4 kainit, on No. 5 both nitrate and super- 

 phosphate, on No. 6 both nitrate and kainit, on No. 7 both super- 

 phosphate and kainit, and on No. 8 all three. When the crop has 

 been ascertained by weighing, comparisons can be made for the 

 effects of using the different fertiUzers singly and with other manures. 

 Supplementary plots will show the best sort and best amoimt of any 

 kind of fertilizer to be applied. 



Purchase of Manures. — ^When buying artificial manures it is 

 important to obtain from the seller a guaranteed analysis, showing 

 the actual percentages of nitrogen, soluble phosphates, insoluble 

 phosphates, and potash. The real worth of a manure may be 

 determined by means of the unit system, and comparison may be 

 made between the real value and the actual price. The unit value 

 is the price of each i per cent, a ton of nitrogen, insoluble phosphates, 

 soluble phosphates, and potash, as the case may be. 



Taking sulphacte of ammonia as a standard, the unit value of 

 nitrogen is calculated at los. to 12s., var5nng with the price. Taking 

 the price at £11 15s., and the percentage of nitrogen at 20 per cent., 

 the unit value = £11 15s. divided by twenty, which is nearly 12s. 



Thus, with I2S. as unit value of nitrogen, of soluble phosphates 

 4s., of insoluble phosphates 2s., and potash 4s., the real value of any 

 manure offered can be calculated. Thus, supposing that a fertihzer 

 was offered guaranteed to contain 9 per cent, nitrogen, 5 per cent. 



