Wheat and its Cultivation. 329 



can be brought about by green manunnfj, as well as by the feeding 

 down of forage crops. Green nuinuring, i.e. the ploughing in of 

 green crops such as peas, rye, vetches, etc., is a much more 

 effecti-ve method of restoring organic matter to depleted soils than 

 the feeding down of forage crops. As, however, the feeding value 

 of a green ci'op is usually greater than its manurial value, the 

 general practice is to convert the crop into milk, mutton, or beef, 

 instead of ploughing it under, No system of crop rotation — however 

 well conceived and carried out — can make up for any shortc-omings 

 in either cultivation or manuring. Crop rotation alone, without 

 adequate manuring, will not increase, nor even maintain, the soil's 

 fertility." 



Rotations for tlie Sontli- Western Wheat Areas of the Cape. — The rotation commonly 

 followed in these aieas is : wheat, usually fertilized ; oats, usually for forage ; grazing- 

 for one or more years followed by " braaking" during winter in preparation for wheat. 



Thus the rotation is tour or five years according to circumstances. Under this system 

 the yields are low, and, moreover, little improvement can be expected so long as it continues. 

 Various experiments were designed by the wiiter at Elsenburg in 1915 to discover a system 

 of farming which would be productive of increased yields and at the same time maintain or 

 improve the fertility of the soil. The results of the past five years indicate two means of im- 

 provement : (1) by the introduction of green imanuring into the rotation ; (2) by the 

 introduction of a leguminous crop, fed off on the land. The experiments fo far show that 

 method (1) gives greater yields, but at greater expense. By method (2) some value is 

 obtained from the crop l)y the stock which feed it off, and this method is therefore recom- 

 mended. 



Manurial Problems: Sources of Plant Food. — "In the case of 

 the wheat crop (straw or grain), of the total amount of food taken in 

 by the crop (1) no less than 93A per cent, is obtained from the air 

 and from the rain ; (2) 3i per cent, consists of mineral substances 

 with which the soil is abundantly supplied ; (3) about 3 per cent, 

 consists of nitrogen, phosphoric acid, and potash, which the soil 

 contains in strictly limited quantities. 



" So far as chemical considerations are concerned, it would 

 appear that a fertile soil is one which contains a sufficiency of plant 

 foods — and particularly nitrogen, phosphoric acid, and potash — in an 

 available or soluble form. Emphasis must be laid on the presence 

 of available plant food, because the greater portion of the plant food 

 is locked up in inert forms, i.e. in forms incapable of being used by 

 the plant. 



Biological Condiiion of Soil. — " Perhaps the most important 

 group of organisms are the nitrifying bacteria. It is interesting to 

 note in this connection that these nitrifying organisms require for 

 their full development: (a) iVir ; (b) warmth — they thrive best at 99 

 degrees F., and are ten times more active at that temperature than at 

 57 degrees F. ; (c) moisture; (d) presence of lime; (e) organic matter. 

 In well-tilled soils, in good " heart " and condition, contaming 

 adequate supplies of carbonate of lime, the useful types of bacteria 

 predominate. In badly tilled soils, sour through want of drainage, 

 or from an absence of lime, moulds, fungi, and harmful types of 

 bacteria flourish to the exclusion of the useful forms. 



" Manuring. — If the soil is deficient in any one of the necessary 

 ingredients, no amount of tillage can put it into good " heart " ; and 

 as the yield of the crop is governed by the amount present of the 

 deficient soil ingredient, it is imperative that the deficiency be made 

 good by the direct application of fertilizers, if satisfactory crops are 

 to be obtained. 



