262 ARTIFICIAL MANURES [chap. 



by the plant, potash tends to keep them growing, 

 especially on light soils and in dry climates, under which 

 conditions it exerts its maximum effects. It is also 

 found to help in stiffening the straw of cereals and grass, 

 and it increases the disease-resisting powers of all plants. 

 But though we can thus distinguish between the 

 effects of the different fertilising constituents, we are 

 rarely able to argue from this knowledge as to the 

 requirements of the particular plants. That we must 

 ascertain by practical experiments, and as an outcome 

 of our fifty years' experience with fertilisers, we now 

 know pretty well the special requirements of our various 

 farm crops. To some extent the manurial treatment of 

 a crop is determined by the place it occupies in the 

 rotation that is being followed. It is comparatively 

 rare to find the same crop occupying the same land year 

 after year, and under ordinary farming conditions the 

 soil very often receives a fertiliser, the effect of which has 

 to extend over several succeeding crops. Again, in con- 

 sidering the amount and nature of the fertilisers to be 

 purchased, the farmer has to take into account the style 

 of his farming, whether high or low. Wherever the 

 land is not naturally rich and the markets are such that 

 the farmer cannot obtain a large return per acre for his 

 crops, he must cut his expenditure down to low limits, 

 and only indulge in purchased fertilisers to a very 

 limited extent. He must follow a conservative system 

 of farming,. being content with comparatively low yields, 

 the material for which has in the main been derived 

 from the soil. We should always remember that the 

 first application of manure is the one which produces 

 the largest increase in the crop, and that if we double 

 the manure bill we shall not obtain a double yield or 

 even a double increase over that which is given by one- 

 half the manure. In fact, if we go on increasing the 



