MULCHED-BASIN SYSTEM OF IRRIGATED CITRUS CULTURE. 31 
the first foot of soil during the summer, but no increase was ob- 
servable at the greater depths. From 70 to 120 days were required 
for the mulch in the basins to decompose sufficiently to produce a 
measurable increase in the humus content. Alfalfa and manure 
mulches were equally effective in producing this increase in humus. 
Barley cover crops produced a marked increase in the humus content 
of the soil 50 days after being disked into the soil. 
The use of an organic mulch moderates the rise in soil temperature 
during the day. The advantages of the mulch, however, are not 
wholly attributable to this fact nor to the conservation of moisture. 
Wood shavings when used as mulching material afforded as much 
protection in this respect as alfalfa or bean straw, yet trees mulched 
with pine shavings gave yields less than half those obtained with 
mulches of alfalfa or bean straw. 
Surface mulching with organic material, especially when available 
in quantities sufficient to cover the entire surface, may in the long 
run prove fully as effective as the use of the mulching material in 
basins. A more immediate response from the mulched basin may be 
expected, however, owing to the fact that each time the basins are 
flooded the soluble portions of the decaying mulch are carried with 
the irrigation water directly into the soil. In this respect the 
mulched basin resembles a surface organic mulch in humid regions 
where the rainfall first passes through the mulch before entering the 
soil. Many of the citrus soils of California contain so little active 
organic matter that it is essential to secure the advantages of the 
applied organic material at the earliest possible date, and this ap- 
pears to be brought about more quickly by the use of the mulched 
basin than by organic mulches with furrow irrigation. The mulched 
basin also appears to be the most effective means of using a limited 
quantity of mulching material. 
The marked response of citrus trees in the experimental tracts 
under the mulched-basin system justifies its serious consideration by 
citrus growers. It is still in the experimental stage, and its suitabil- 
ity to local conditions in any instance should be thoroughly tested 
in an experimental way before installing basins on a large scale. Its 
final value in the industry can be determined only after it has been 
so tested in comparison with other systems in commercial practice. 
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