Salt effects on transplant mortality, growth and rubber yields of guayule

Summary

Because of the strategic and industrial importance of natural rubber, there has been renewed interest in cultivating guayule (Parthenium argentatum). This study was performed for assessing feasibility of guayule cultivation with waters high in dissolved salts. The test materials included six USDA selections (11591, 11605, 11619, 11646, 12229 and N576), one cultivar (593) and one hybrid (4265XF). Seedlings were grown for l0 weeks in a greenhouse and transplanted in the spring and in the summer into lysimeters (unit surface dimension of 6 x 7 m) containing loamy sand or silt loam. They were grown with simulated irrigation waters having four levels of salinity (0.8, 2.4, 4.6 and 7.2 dSm⁻¹ with SAR < 13) and an additional water containing 5 mmol L⁻¹ of Mg at 2.4 dSm⁻¹. In the spring planting, over 90% of the transplants survived when furrow irrigated weekly with waters of 4.6 dSm⁻¹ or less. However, transplant growth for the first several months was reduced by half at irrigation water salinity of 4.6 dSm⁻¹. In the summer planting, several fold increases in mortality and growth reduction occurred. Dry top Shrub yields after the two growing seasons following the spring planting averaged 10 Mg ha⁻¹ at 0.8 dSm⁻¹ and declined on the average 15 and 51 % when irrigated with waters of 4.6 and 7.2 dSm⁻¹ respectively. The amount of water used to produce one ton of dry shrub was 1,600 m³ with waters of 0.8 and 4.6 dSm⁻¹, and 1,900 m³ with water of 7.2 dSm⁻¹. The contents of rubber in the shrubs averaged 61 g kg⁻¹ at 0.8 dSm⁻¹ and increased to 70 g kg⁻¹ at 7.2 dSm⁻¹. whereas resin contents were not affected by the salt treatments. Resulting rubber yields were reduced on the average by 8.5 and 44% at 4.6 and 7.2 dSm⁻¹. respectively, because of the reduction in shrub yields. Selection N576 produced the largest rubber yields with the highest rubber content at all levels of salinity. Increasing Mg concentrations from 0.5 to 5 mmol L⁻¹ in the irrigation waters reduced neither yields nor transplant survival. Yield reductions observed here appeared to be related to Na, but not Mg.