SUMMARYThe growth of foxtail millet and clover in soils of varying degrees of salinity (0.5 to 13 mmhos/cm), treated with nitrogen and phosphorus, was studied. Salinity levels were achieved by addition of sodium chloride. Nitrogen (10 to 60 ppm N) and phosphorus (6.4 to 44.8 ppm P) were added as NH4NO8 and I-I3PO4, respectively.The growth of millet decreased sharply with increase in soil salinity, when N -P treatments were not applied. The development of this plant altered under saline conditions, however, when nitrogen and phosphorus were added; various N -P combinations affected plant growth in saline soil differently. Phosphorus, when applied at relatively high rates, significantly improved plant growth.Increased rates of nitrogen in the N -P treatments generally had no significant effect on growth; it was reduced when the N/P ration was highest.Clover ceased to grow when the salinity of the soil exceeded 7 mmhos/cm and no N -P was added. Phosphorus enhanced the growth of clover, and at high rates of its application in the N -P combinations, clover grew even at the highest salinity level tested (13 mmhos/cm). Nitrogen increase had no marked effect on plant development.Comparing enhancement of growth at high salinity levels, clover was somewhat less affected by the N -P treatment than millet.The top/root ratio of clover generally increased with increase of phosphorus in the N -P combinations.
Prolonged commercial irrigation with treated sewage effluents from rural sources resulted in accumulation of heavy metals in the top 10‐ to 15‐cm layer of the soil in three commercial fields. Statistically significant differences were found for total content and extractable fraction of Cd in all three soils, and for Cu, Ni, and Pb in clay soils by comparing these fields and adjacent ones irrigated with normal water. Chromium concentration differences were not statistically significant. As a result, there was some increase in the concentration of these elements in Rhodes grass (Chloris gayana Kunth.) grown in the sewage‐effluent‐irrigated fields as compared with the grass grown in the fields irrigated with normal water. The increase, although statistically significant, was slight, even in the field that had been irrigated with sewage effluents for up to 28 years. The uptake of the various metals, as assessed by the enrichment factor (EF = µg element g−1 plant/µg element g−1 soil), tended to diminish with an increase in the specific surface area of the soil. This was particularly pronounced with the more labile of the elements studied—Cd, Cu, and Ni—and less so for Pb and Cr. The uptake of a given element appears to be largely determined by its solubility in the soil solution and can be generally predicted by its ionic potential. The relative magnitude of the enrichment factor established for Rhodes grass is in the following order: Cu > Cd > Pb > Ni ≫ Cr.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.