MULCIIED-BASIN SYSTEM OF IRRIGATED CTTRUS CULTURE. 

 FURROW IRRIGATION OFTEN NOT ADEQUATE. 



13 



The furrow system of irrigation often fails to provide the moisl lire 

 necessary for good growing conditions for orange trees in the heavier 

 types of soil. This was strikingly shown dining the season of l!)lfi, 

 many orange groves wilting between irrigations. At one time dur- 

 ing the summer a grove adjoining the Victoria grove showed wilt- 

 ing for several days before irrigation. Soil samples were taken at the 

 time to determine the percentage of moisture present. The results 

 are shown in Table VI, the moisture-determination figures represent- 

 ing the average moisture content to a depth of 3 feet of soil. 



Table VI. — Moisture conditions under wilted orange trees. 





Moisture 

 equiva- 

 lent. 



Wilting 

 coeffi- 

 cient. 



Av rage moisture. 



Condition of leaves. 



In soil. 



Availa- 

 ble. 





15.6 

 15.1 



8.5 

 8.2 



Per cent. 

 6.9 



7.1 



Per cent. 

 —1.6 



Leaves on top third of tree badly wilted, lower two-thirds not 



- .1 







The moisture determinations include the dry surface soil, which 

 through surface evaporation dries out to about one-half the wilting 

 coefficient, so that the average moisture content of the 3-foot section 

 is about nine-tenths that of the soil actually occupied by the tree 

 roots. The second tree mentioned in Table VI had been wilted for 

 several days preceding the sampling. These observations, on heavy 

 soil and similar observations on light soil show that the wilting 

 coefficient determined indirectly from the moisture equivalent of a 

 soil agrees satisfactorily with direct determinations made in the 

 groves. 



LATERAL MOVEMENT OF SOIL MOISTURE VERY SLIGHT. 



The lateral movement of moisture in the heavy soils of the Vic- 

 toria tract is very slight. After an irrigation considered sufficient 

 to last about 28 days, the moisture was found to have penetrated 

 laterally only about 18 inches from the irrigation furrow. In other 

 words, there is practically no lateral movement of water toward 

 the tree, the feeding roots being confined to the soil below the irri- 

 gation furrows. 



The lateral movement of water was also found to be very slight in 

 a basined grove at Redlands located on the same type of soil as the 

 Victoria grove just discussed. Soil samples were taken on May 26, 

 before the first spring irrigation, and the day after the grove was 

 irrigated samples were again taken within a few inches of the first 

 samples. Alfalfa was being grown in the furrows between the 



