Soil-salinity studies as related to sugarcane growing in southwestern Puerto Rico

Abstract

The salinity problem of Lajas valley in southwestern Puerto Rico has developed from seepage caused by impeded drainage and by surface-soil evaporation because the salts from the salty wells used for irrigation and the run-off drain toward the lowlands. A project is under way in Lajas valley to irrigate about 24,000 acres of good cane land. Salts also affect adversely the growth of sugarcane on about 10,000 acres in addition. The salty lands include saline, saline-alkali, and nonsaline alkaline soils. Saline soils contain excessive salts and alkaline soils contain excessive exchangeable sodium. The excess of salts in the saline and saline-alkali soils can be leached out by fresh water if good drainage is provided, as was shown by three leaching tests performed in the field. The excess of salts in the saline-alkali soils and the excess of sodium in the saline-alkali and nonsaline alkaline soils may be leached out with gypsum or sulfur and fresh water, if good drainage is provided, and if the exchangeable sodium to be removed is not excessive, that is about 5 m.e. per 100 gms. of soil. The high content of extractable or exchangeable calcium generally present in the salty lands of Lajas valley is a good asset for their successful reclamation with fresh water and chemicals such as gypsum or sulfur, if adequate drainage is provided. In a field test, an application of 2 tons of gypsum per acre produced a significant increase in cane yield, but the acid juice of the cane was salty. Sugarcane grows poorly in the salty lands of Lajas valley that contain from 0.75 to 2.00 p.p.m. of available boron, from 0.53 to 1.19 percent of sodium chloride, from 20.0 to 72.9 percent of extractable sodium, from 2.5 to 3.1 calcium-sodium ratios, and the pH of which ranges 8.3 to 9.2. Good sugarcane growth was observed when the salty land contained 4.5 to 11.4 of extractable sodium and the calcium-sodium ratios were 12.0 to 19.4.