The growth and rubber content of guayule as affected by variations in soil moisture stresses
1946
Hunter, A.S. | Kelley, O.J.
Irrigation experiments on guayule in its second year of growth in the field were conducted on two soil types, the Delano sandy loam and the Sorrento silty clay loam, in the San Joaquin Valley of California. Five similar variations in moisture level, ranging from very high to very low, were maintained on each soil type from the first of April to the first of October. Soil moisture records are presented. Plant samples were taken for dry weight and rubber determination at the beginning of the experiment and at three later dates. There was an inverse relationship between dry weight of shrub and rubber percentage. When all plots are considered, the applications of fertilizers increased the weight of shrub but decreased the percentage and the absolute amount of rubber. On the sandy loam soil, the highest yields of shrub and rubber per acre were given by the plots maintained at the higher levels of moisture; on the silty clay loam, the highest rubber yields were produced on the plots having the lowest moisture levels. Some possible reasons for the discrepancy are discussed. On plots of the highest moisture levels, the rubber percentage was lower at the end of the experiment than at the beginning. Increases in shrub weight during the season ranged from 1,000 to more than 10,000 pounds per acre. Increases in the amount of rubber ranged from 190 to 650 pounds per acre on the sandy loam and from 350 to 515 pounds on the silty clay loam. Moisture treatment had small influences on the percentage of resin in the shrub.
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