Subirrigation Research Articles

Introduction Production of sugarbeets on highly organic soi ls of the Delta region at the mouths of the Sacramento and San Joaquin Rivers of California poses some special problems not encountered on mineral valley soils. The water table is generally within 3 or 4 feet of the ground surface, the topography is very flat and both the moisture and nutrient-supplying characteristics are markedly different from those of mineral soi ls. The high permeability of the organic soils prevents furrow irrigation, and the most com mon practice is to su hirriga te by controll ing the water ta bl e level 'w'ithin narrow limits throughout the season. Previous experiments and observations have pointed to the need for simultaneous improvements In both moisture and nutrient supply. In 1953, an experiment comparing subirrigation alone 'with subirrigation plus supplemental sprinkling was con ducted. There ,as no response to supplemental sprinkling, but analysis of petioles taken at regular intervals indicated a severe phosphorus deficiency by mId-season. Field trials in 1936, 1959 and 1960 indicated that fertilize'r phosphorus was readily taken up by sugarbeets under supplemental sprinkler irrigation . There' were yield responses as well as increases in petiole phosphorus when phosphorus deficient soils were fertilized . A fi~ld experi ment in 1961 demonstrated uptake of phosphorus placed 10 or 16 inches deep by plants grown with su birrigation only. Evalua tion was by petiole analysis. In this trial, howevff, drough t, uitrogen deficiency and virus yellows resulted in lo'w yields for all treatments. It had been observed that under subirrigation an appreciable depth of soil became quite dry and that beets lost older leaves and ,viI ted occasionally on hot days. Because of virtual lack of detailed information on soil moisture conditions and soil char acteristics important in supplying plants ,vith water, a detailed evaluation was undertaken. The importance of this was further

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