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 <li" 

 sandy loam soil. 



Table VIII. — Average available soil moisture to a depth of S feet in sandy 

 loam (Vivienda grove) and, in clay loam, (Victoria grove) after irrigation. 



Soil treatments. 



Clay 

 loam. 



Sandy 

 loam. 



Soil treatments. 



Clay 

 loam. 



Sandy 



loam. 



Manure: 



Per cent. 

 7.3 

 7.6 



6.6 



8.8 



Per cent. 

 6.9 

 7.9 



6.0 

 7.3 



Sweet clover: 



Per cent. 

 4.2 

 5.2 



2.2 

 1.4 

 4.0 



Per cent. 

 8.2 







6.7 



Alfalfa: 



Barley: 



7.5 







6.5 







0.5 









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 Belief ourche 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 



