146 ACTION OF SOIL ON FOOD OF PLANTS IN MANURE. 



parts of a dung-heap, the analysis of each sample will 

 show different proportions of nutritive constituents : 

 hence it is evident that by a dressing with i arm-yard 

 manure hardly two spots in the soil will receive the 

 same amount of nutritive substances. 



The spot occupied by a dung-heap on a field during 

 rainy weather, will be marked in the whole period of 

 vegetation, and often even in the second year by a more 

 luxuriant growth of plants, especially of cereals, though 

 the plants growing on it will not always furnish a per- 

 ceptibly greater yield of grain. If the potash and am- 

 monia received by this spot above what was required 

 for the formation of grain, had been more evenly 

 distributed, and thus accessible to the plants in other 

 places, the yield of corn from those plants would have 

 been increased ; whereas the excessive accumulation in 

 one place merely increased the yield of straw. The 

 unequal distribution of the other ingredients of farm- 

 yard manure in the soil leads to a similar inequality in 

 the developement of the several parts of the cereal 

 plants. On an ideal field, with the nutritive substances 

 supposed to be distributed with perfect uniformity, and 

 all accessible to the roots, all the cereal plants, other 

 conditions being the same, should attain the same 

 height, and each ear yield the same number and weight 

 of grains. 



In the short, rotten farm-yard manure, the nutritive 

 substances are much more uniformly distributed than 

 in the fresh straw manure ; and the agriculturist effects 

 a still more uniform diffusion by mixing the dung with 

 earth, and turning it into so-called compost. As dung 

 and all other manuring agents act only through the 

 medium of the earthy^ particles that have become sat- 

 urated with the nutritive substances contained in the 

 manure, it is, under certain -circumstances, advanta- 

 geous for the farmer to prepare a saturated earth, by 

 help of his farm-yard manure, and to use this composi- 

 tion, which may of course be made on the field itself. 

 If, in accordance with Yoelker's valuable experiments, 

 we assume one cubic metre ( = 35 cubic feet) of farm- 



