The effect of Ni pretreatments on the yield and concentration of Ni in oats and alfalfa grown in four soils in pot tests varied with the rate of added Ni, with lime and phosphate treatments, and with soil properties, notably pH and organic matter content. The concentrations of Ni in the crops showing repressive effects of added Ni were at least 60 ppm in the oat grain, 28 ppm in the oat straw, and 44 ppm in the alfalfa. The amounts of soil-extractable Ni and the concentrations of Ni in the plants were reduced by liming of the acid soils and they tended to be increased by addition of phosphate. The effects of the Ni pretreatments on growth were less severe in a neutral soil and in one containing considerable organic matter than in the others.
The concentrations of Pb in five species of plants were found to increase with proximity of the sampling sites to a well-travelled highway.The Pb content of oats and alfalfa grown in four soils pretreated with PbCl2 in pot tests varied inversely with the organic matter content and pH of the soils. The amounts of Pb taken up by the plants were reduced upon addition of phosphate or of lime to the acid soils. Furthermore, the beneficial effects of organic matter, phosphate and lime in reducing Pb in the plants were usually in accord with corresponding reductions in extractable Pb in the soils as measured in 1 N neutral ammonium acetate and 0.1 M CaCl2.
Foliage of three grasses and three legumes, grown in a greenhouse, was treated with gibberellin solution and yield response evaluated. In general, the first cut yields of these grass and legume species were increased by gibberellin. With legumes the maximum yields were obtained at the highest rate of application. Maximum yields of grasses were obtained with rates less than the highest. Generally speaking there were reductions in second-cut yields of the grasses and legumes tested with higher rates of gibberellin. Treatment of the foliage with gibberellin decreased root weights m every case.There were significant negative correlations between total top and root weights of all species, except two in which there were no correlations. The per cent protein of all grass and legume species was decreased with gibberellin treatments. However, because of increased dry matter, highest yields of protein were generally obtained with treatments producing highest dry matter yields. The per cent ground cover of the species treated decreased progressively with increased rates of gibberellin.
Established stands of three grasses and legumes, grown in a greenhouse, were subjected to flooding treatments consisting of soil moisture tensions of approximately 0, 25 and 40 centimetres of water which were equivalent to field conditions where the water table is at the soil surface, 25 and 40 centimetres below the soil surface, respectively. Herbage and root yields were measured.Grasses were more tolerant to flooding than were the legumes. The order of decreasing tolerance to flooding was: reed canary grass, timothy, brome grass, birdsfoot trefoil, Ladino clover and alfalfa. The yields of grasses tended to increase with increasing moisture levels and with durations of flooding, whereas the yields of legumes tended to decrease with increasing moisture levels and with the duration of flooding.The effect of flooding on yields was more pronounced on the first than on the second harvest. Highly significant positive correlation coefficients were obtained between total top and root weights of reed canary grass, birdsfoot trefoil, Ladino clover and alfalfa. Corresponding correlation coefficients for timothy and brome grass were negative and highly significant.Oxygen diffusion measurements indicated that, in general, the yields of legumes increased with increasing availability of oxygen whereas the yields of grasses showed a tendency to decrease. As the soil temperature under flooding conditions increased from 41° to 80°F. the forage yields usually decreased.
Young seedlings of flax and cereals, grown in a greenhouse, were subjected to 0, 12.5, and 25.0 cm of soil moisture tension for periods of 7, 14, and 21 days The grain, straw, and root yields of all plant species, except barky, increased with increasing soil moisture content was maintained near field capacity during the growth of plants. The yields of oats, winter wheat, and fall rye decreased with increasing duration of flooding, whereas those of barley, flax and spring wheat were variable. Correlation coefficients between yields of tops and roots were positive.
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