UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 499 



Contribution from the Bureau of Plant Industry 

 WM. A. TAYLOR, Chief 



Washington, D. C. 



PROFESSIONAL PAPER 



February 12, 1917 



THE MULCHED-BASIN SYSTEM OF IRRIGATED 

 CITRUS CULTURE AND ITS BEARING ON THE 

 CONTROL OF MOTTLE-LEAF. 1 



By Lyman J. Briggs, Biophysieist in Charge, C. A. Jensen, Assistant in Plant 

 Malnutrition Investigations, and J. W. McLane, Laboratory Assistant, Office 

 of Biophysical Investigations. 



CONTENTS. 



Page. 



Introduction 1 



Cultural practice in the citrus districts of Cali- 

 fornia 3 



Plowsole 4 



Organic mulching 4 



The mulched basin 6 



Moisture determinations in the Sunny Moun- 

 tain grove 7 



Soil-moisture measurements in basins, under 

 cover crops and under a soil mulch in tho Viv- 



ienda grove 8 



Basin and cover-crop experiments in the Vic- 

 toria grove 11 



Furrow irrigation often not adequate 13 



Lateral movement of soil moisture very slight. . 13 

 Summer cover crops in orange groves not prac- 

 ticable withoutan increased water supply 14 



Page. 

 Organic mulches more effective than soil 



mulches in conserving water 14 



Effect of basining on tree growth 15 



The mulched basin in relation to soil type 1G 



Effect of the mulched basins on soil conditions 



and root growth 17 



Fruit setting and tree growth as influenced by 



the mulching material 18 



Size of basins 23 



Cost of preparing and maintaining the basins 



and the mulch 24 



Limitations of the mulched-basin system 25 



Humus content of the basins and the check 



soils 26 



Summary 28 



INTRODUCTION. 



Orange and lemon trees in California are subject to a functional 

 disturbance known as mottle-leaf, which in its advanced stages 

 results in a marked reduction in the yield and quality of the fruit. 

 The characteristics of mottle-leaf have been discussed in a recent 



1 The writers take this opportunity to express their obligation to the University of 

 California Citrus Experiment Station and Graduate School of Tropical Agriculture at 

 Riverside for the courtesies and facilities extended during the course of this work, 

 and to the growers who have placed groves at the disposal of the Government for 

 experimental purposes and who have provided the labor and materials necessary for 

 the prosecution of the field experiments. 

 68279°— Bull. 499—17 1 



