MULCHED-BASIN SYSTEM OF IRRIGATED CITRUS CULTURE. 17 
clay-loam soils where cover crops are grown or where the soil is 
cultivated. On the other hand, under the basin system the heavy 
soil has a little more available moisture after irrigation than the 
sandy loam soil. 
TABLE VIII.—Average available soil moisture to a depth of 3 feet in sandy 
loam (Vivienda grove) and in clay loam (Victoria grove) after irrigation. 
Soil treatments. eee candy Soil treatments. oe paney 
Manure: Per cent. | Per cent. || Sweet clover: Per cent. | Per cent. 
HIME ASINS\2 32 See ae Seema ae 6.9 Covercropeeesssa-s 42 oee 4.2 8.2 
Same, plus lime......---- 7.6 7.9 Same, pluslime....---..-- 5.2 Os 7 
Alfalfa: : Barley: 
mebaSinS@2es-se oss eee 6.6 6.0 COWeniChO peas eee eee 2h2 de 
Same, pluslime....----.. 8.8 7.3 Same, plus lime........-- 1.4 6.5 
Cultivatedseeecsaa- cose 4.0 6.5 
Where groves are planted on heavy adobe soils, as is the case with 
some groves near Whittier, the use of the mulched basins has been 
found inadvisable. Heavy adobe soil swells when thoroughly 
moistened, and in this condition is practically impervious to water 
and to air. In the case of heavy adobe soils (derived from Pierre 
shale) on the Bellefourche Reclamation Project in South Dakota, 
it has been observed that the irrigation is effective only so long as 
the shrinkage cracks are in evidence. The water is distributed 
through the soil by means of these openings, and when the adobe 
has swelled sufficiently to close the cracks the soil will take no more 
water. ‘The use of mulched basins on heavy adobe results in a more 
nearly uniform moisture condition at the surface and prevents the 
development of surface cracks. These fissures appear to be essential, 
or at least desirable, for the proper irrigation and aeration of heavy 
adobe. On the same ranch near Whittier, Cal., where the difficulty 
with heavy adobe was encountered, lemon trees on soil of a less pro- 
nounced adobe character have shown a most favorable response to 
the mulched-basin treatment. 
EFFECT OF THE MULCHED BASINS ON SOIL CONDITIONS AND 
ROOT GROWTH. 
In all the experiments carried on with mulched basins having an 
area as large as the spread of the tree, irrigation once a month has 
been sufficient to maintain a good soil-moisture condition throughout 
the period between irrigations. The mulch also tends to maintain a 
moderate and more uniform soil temperature, and in this respect it 
is aided materially by the location of the irrigated area largely under 
the tree, where it is shaded by the tree top. The plowsole nearly 
always present in the furrow and cultivation method of treatment 
also disappears in the mulched basin, and so far no plowsole or 
