364 EXPERIMENTAL STATIONS — TURNIP CROP 1882. 



The first thing to notice here is that the dissolved phosphates 

 have again, as in former occasions, produced a larger crop. At 

 Pumpherston the difference is 17 per cent, and at Harelaw 8 per 

 cent, in favour of the dissolved phosphate, so far as mere gross 

 weight of turnips is concerned. 



The difference between the winter and summer manured 

 plots is not very striking. On the whole, it is in favour of the 

 early application of manure, but it must seem a remarkable 

 circumstance that the plots which received dissolved phosphates 

 have gained most by early manuring. The object which one 

 would naturally have in view in applying an insoluble manure 

 some months before sowing the seed, would be to give it time to 

 dissolve in the soil before the coming of the roots of the crop. 

 In all fertile soils chemical changes are going on which have 

 the effect of rendering the insoluble phosphates contained in 

 them, or added to them as manure, more easily attackable by the 

 roots of plants, and the nature and composition of soils possess- 

 ing that character in a high degree, have been the subject of 

 special study by various chemists. Soils rich in organic matter 

 are especially found to possess that property, and it will be seen 

 that the soil at Harelaw which is richer in organic matter than 

 that of Pumpherston, has profited to some extent by the earlier 

 application of insoluble phosphates ; while the latter soil, which 

 is more clayey with a tilly subsoil, has had the effect of diminish- 

 ing rather than increasing the solubility of the raw phosphates. 

 AVith the dissolved phosphates the case has been different. At 

 both stations the early application of superphosphate has been 

 advantageous, but especially so at Pumpherston. This is an 

 unexpected result. One would naturally have supposed that the 

 sooner the soluble phosphate came in contact with the roots of the 

 crop the more rapid and effective would be its action. On the other 

 hand, we must remember that soluble phosphates when applied to 

 the soil are very rapidly precipitated or rendered insoluble by com- 

 bining with the lime, oxide of iron, and alumina contained in the 

 soil, and it is highly probable that little or none of the phosphate 

 is taken up by the roots of plants until it has been precipitated. 

 The roots of plants themselves are able to dissolve some forms 

 of insoluble phosphate very readily, and it is probable that 

 during the winter the soluble phosphate was more widely and 

 uniformly precipitated than that applied with the seed. There 

 are other circumstances which must not be lost sight of in 

 endeavouring to explain this result, viz., that the superphosphate 

 in these plots was not applied alone, for potash salts accom- 

 panied it, and that in superphosphate itself we have sulphuric 

 acid as well as phosphoric acid to consider. It might be 

 explained that the advantage was not directly due to any im- 

 provement in the condition of the phosphate, but indirectly to 



