Chemical changes in an irrigated soil during 28 years of differential fertilization

Abstract

Abstract does not appear. First page follows. Introduction One of the most extensive long-term fertility trials on irrigated soils in a semiarid region is the fertilizer experiment with citrus being conducted at Riverside. The purposes of the experiment were to study the effects of a variety of fertility levels and treatments on yield, growth, and behavior of trees, to measure the cumulative and secondary effects of fertilizers on the trees, and to study the effects of fertilizers, soil amendments, and irrigation on properties of the soil. The purpose of this paper is to report changes in the chemical properties of the soil that have resulted from irrigation and differential fertilization. Description of the experiment Washington Navel oranges on sweet orange rootstocks were planted for this experiment in 1917. The land had been previously dry-farmed but had not been fertilized or irrigated. During the first ten years of the growth of the trees fertilizers were not used. During this period winter covercrops of yellow bitter clover or of purple vetch were grown annually, and during the first six years, summer covercrops of cowpeas were grown. The winter cover-crops used since 1927 have been dominantly vetch with barley. In 1927, differential treatments of the plots were begun. (Parker and Batchelor (1932))6 described the method of distributing the plots to the various treatments. Each plot consisted of a row of eight Washington Navel