160 Barn-yard Manure. 
Gypsum.—Gypsum, or land plaster (sulphate of lime), occurs 
in considerable quantities in this Siate and Nevada, and is now 
being mined and ground at a low price in the San Joaquin Val- 
ley. 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 every- 
where 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 fermentation, and it is, therefore, not a desirable addi- 
tion 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. 
Marls.—Mar! is a calcareous earth, and is called shell marl, 
rock marl, earthy marls, etc., according to its origin and mechan- 
ical condition. A number of samples from different parts of 
the State have been analyzed by Professor Hilgard, and some of 
them commended for local application to soils needing lime, but 
not valuable enough to warrant hauling far. 
BARN-YARD 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 ex- 
tent, 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 there are certain amounts of material avail- 
able from the animals that are kept for cultivation and hauling, 
or to be had, often, for the expense of hauling from adjacent 
towns. 
As already stated, coarse, unrotted manure can seldom be 
used to advantage in this State unless it be in heavy soils in 
regions of ample rainfall, or on lighter soils, perhaps, if well irri- 
gated; and even in such situations either finely-divided or well- 
rotted manure is infinitely superior. Corral scrapings, which 
are usually the first recourse when the idea of manuring springs 
up in a neighborhood, are not always well decomposed, but they 
are finely divided, and therefore decompose readily as compared 
