VARIOUS FORMS OF LIME 145 



in another connection, the use of lime as a top dressing, at the rate of 

 six hundred to one thousand pounds to the acre, not only makes the 

 heavy soil more friable, but acts upon and makes available the large 

 amount of organic matter which such soils usually contain. Lime also 

 renders inorganic materials more available for plant food, corrects 

 acidity, and may destroy insects and fungi. Application of lime is 

 also desirable after applications of barnyard manure have been made 

 for several years; and it is especially valuable wherever, in alluvial 

 soils rich in vegetable matter, there is an excessive growth of wood 

 and leaf. Usually light soils are not materially benefited by the use 

 of lime. 



Ground limestone is gaining standing as a fertilizer. It acts less 

 vigorously and -more slowly than burnt lime or hydrate of lime in 

 improving heavy soils, but it serves a good purpose in overcoming 

 sourness in loams, silts or sands. It should be used in double the 

 amounts prescribed for other forms of lime. 



Gypsum. Gypsum, or land plaster (sulphate of lime), occurs 

 in considerable quantities in this State and Nevada. It acts directly 

 in correcting soils made alkaline by presence of carbonate of soda. 

 Applied to soils not alkaline, gypsum sets free potash, magnesia, and 

 ammonia, which may be present in insoluble form; and it also causes 

 potash to be transferred from the upper to the lower layers of the 

 soil, so that roots can everywhere find a store of it. Hence its special 

 value when applied to deep-rooting plants. The reason why gypsum 

 is so capricious in its action, which was long a mystery, is now held 

 to be clear, because upon soils that are tolerably rich in fixed potash 

 it will do good service, while upon soils poor in potash it will not. In 

 any event gypsum is to be regarded as an excitant rather than as a 

 form of plant food. 



Of the several uses of gypsum, probably its chief value lies in its 

 power as an absorbent. If added to manure in excess it delays fermen- 

 tation, and it is, therefore, not a desirable addition to the compost heap. 

 But for covering fermenting manures or scattering around moist places 

 in horse and cow stables to absorb odors and fix volatile manurial 

 substances it is of value. Gypsum does not correct acidity nor does it 

 promote decay of organic matter as other forms of lime do. 



Marls. Marl is a calcareous earth, and is called shell marl, rock 

 marl, earthy marls, etc., according to its origin and mechanical condi- 

 tion. A number of samples from different parts of the State have been 

 analyzed and some of them commended for local application to soils 

 needing lime, but they are usually not valuable enough to warrant 

 hauling far. 



BARNYARD MANURE AND COMPOST 



Where fruit growing is carried on with stock growing, there are 

 abundant supplies of manure available, but this combination is not 

 characteristic of California, though prevailing to some extent, and 

 likely to be more prevalent as fruit planting extends farther from the 

 centers which are wholly given to it. But even in the fruit centers 



