lo June. 19 io.] 



Limiting Factors in Agriculture. 



357 



disced twice, and manured with one hundred-weight of superphosphate per 

 acre. It \vas grown at Box Hill on a soil consisting of a fine, dust-hke 

 sand, with a clayey subsoil. The latter has the peculiarity of baking very 

 hard in drv weather, and the former of setting after xain and also bakmg 

 ^•erv hard after dry weather if not worked Hence, as can be seen in the 

 photograph, the soil remained full of clods. It did not retain its moisture 

 well, and the subsoil dried hard, preventing the roots penetrating deeply, 

 and giving a stunted growth of the crop. The land for the maize in the 

 second photograph was similarlv prepared, but in addition, the clods were 

 partly broken and it was hoed thrice instead of once. No manure at all 

 was applied, but it was easy to see the superior effect of the physical 

 treatment on the crop as contrasted with the effect of a mineral manure. 

 In addition, the subsoil remained softer than in the previous case, the soil 

 itself was moister a few inches in. ami the root svstem was larger and 

 penetrated more deeplv. 



MAIZE (SIBLEV) IN WELL WORKED SOIL WITHOUT MANURE. 



In the case of the maize shown in the third photograph, these diffexences 

 were still more marked and were simplv and solely the result of continually 

 working the soil so as to keep it open and well aerated, at the same time 

 maintaining a fine du.st-like soil mulch on the surface. As in the second 

 plot, neither manure nor water was given to the maize grown in this plot. 



The results speak for themselves. In fact, in the case of all crops, 

 the working of the soil to enable it to retain moisture and to maintain its 

 aeration, so encouraging the formation of a large joot system, is vastly 

 more important as a prime factor in plant development than is any amount 

 of manuring wdth chemical manures. Indeed, w^ie.re the supply of water 

 is scanty, the use of a soluble chemical manure may even be injurious, 

 since it mav cause a saline concentration in the soil sufificient to injure the 

 roots, retard their development, and make it more difficult for them to 

 absorb water. Such actions are most shown in sandy soils, and less so 

 in the presence of humus, which is, in fact, one of the best correctives a 



