L. H. Stolzy

Influence of soil oxygen and soil water on the accumulation of nutrients in avocado seedlings (Persea Americana mill.)

SummaryThis experiment was conducted in a greenhouse to study the influence of 2 soil-oxygen levels and 4 irrigation levels on the plant response, root decay, concentrations of 12 nutrients, as well as on total amounts of nutrients per avocado seedling (Persea americana Mill.).Reduced soil-oxygen supply to the roots significantly reduced the amount of dry weight per seedling, increased percentage of root decay, and reduced the concentrations of N, P, K, Ca, Mg, and B in the tops, while Na and Fe were increased. Concentrations of K, Mg, Na, and Cl in the roots were decreased, while N and Ca were increased with decreased soil oxygen supply to the roots. Total amounts of N, P, Ca, Mg, Na, and Cl per seedling were decreased with the low soil-oxygen supply to the roots.Only slight differences in dry weight of the tops of seedlings were found. The highest degree of root decay was caused by the irrigation treatment where a water table was present. In the tops, concentrations of N, P, K, Mg, Na, Zn, Cu, Mn, B, and Fe were significantly influenced by differential irrigation treatments; in the roots, concentrations of P, K, Ca, Mg, Na, and Cl were also significantly influenced; and total amounts of N, P, Mg, and Cl the whole seedling were likewise significantly influenced.Significant interactions were noted between the soil-oxygen and irrigation treatments on the dry weight of tops, roots, and total amounts of dry weight produced per seedling. The lowest amount of dry weight of roots and the highest degree of root decay were found in the avocado seedlings grown under low soil-oxygen supply and the irrigation treatment where a water table was present. Several significant interactions between soil oxygen and irrigation on the concentrations of N, P, K, Ca, Zn, and Mn are discussed.

GROWTH AND NUTRIENT UPTAKE OF NEWPORT BLUEGRASS AS AFFECTED BY SOIL OXYGEN

SummaryAn oxygen diffusion rate of 20×10−8 g cm−2 min−1 is required for root growth of Newport bluegrass. The optimum O.D.R. is in a range above 40.During the first growth period, the vegetative growth was not greatly affected by oxygen treatment except during the <1% treatment which did not permit root growth. After clipping, the growth increased with increasing oxygen to a maximum at the 10% treatment and then exhibited a lower growth under the 21% treatment. The plants survived through all oxygen treatments.The concentration of N, P, and K in the leaves generally increased with increased oxygen supply. Na accumulated to a high concentration under the lowest oxygen treatment.

INFLUENCE OF SOIL-OXYGEN DIFFUSION RATES ON SUSCEPTIBILITY OF TOMATO PLANTS TO AIR-BORNE OXIDANTS

Tomato plants established in containers of soil with different oxygen diffusion rates were subjected to airborne oxidants for short periods of time. The supply of oxygen to plant roots, or the oxygen diffusion rate, influenced the susceptibility of plants to airborne oxidants. Plants growing in soils with oxygen diffusion rates of 16 to 24 x 10/sup -8/ g. cm./sup -2/ min./sup -1/ were not damaged by peroxyacetyl nitrate (PAN) or ozone. Plants growing in soils with oxygen diffusion rates of 34 to 90 x 10/sup -8/ g. cm./sup -2/ min./sup -1/ were moderately to severely damaged by both PAN and ozone. Water-use data and plant symptoms were an indication of reduced plant vigor at the lower-oxygen treatments. Soil oxygen diffusion rates taken in field plots show that limited oxygen supply to plants could affect the susceptibility of plants to airborne oxidant damage under field conditions. 9 references, 3 figures, 2 tables.

Impact of potassium, sodium, and salinity on the protein-and free amino acid content of wheat grain

A lysimeter study was conducted on Cajeme wheat (Triticum aestivum L.) to investigate the impact of salinity on protein and free amino acid content of the grain. Cross correlations were obtained between 16 different soil-plant-water based parameters and the concentration and total accumulation of amino acids.The results indicated that after 3 years of irrigation, the majority of protein bound and free amino acids increased in concentration in the grain. However, both free tryptophan and free proline revealed decreasing concentrations with increasing salinity. Free tryptophan showed a synergism between total accumulation, yield and concentration. Free proline concentrations decreased in association with increasing protein concentrations.Cross correlations of the 16 soil-plant-water based parameters with free and protein bound amino acids revealed significant correlations for free aspartic acid and glycine with total accumulation but not with concentrations. Only methionine plus cystine was lower than suggested FAO levels for essential amino acids and was lower in the third year than in the first year.

EFFECT OF ROOT INFECTION BY PHYTOPHTHORA CINNAMOMI ON NUTRIENT UPTAKE AND TRANSLOCATION BY AVOCADO SEEDLINGS

Infection of avocado seedling roots by Phytophthora cinnamomi greatly increased the root decay, decreased the dry weight of roots by 86 percent, stems by 89 percent, and leaves by 82 percent as compared with the values obtained from the uninfected plants. Presence of the fungus in the roots of avocado seedlings caused drastic changes in nutrient concentrations found in the roots, stems, and leaves. This indicated that the fungus in the roots of the plants not only influenced nutrient uptake from the soil but, also, the distribution of nutrients within the plant parts. Regardless of the concentrations of various nutrients found in the avocado plant tissues, the total amounts of each nutrient/plant under consideration were found to be significantly less in infected plants than in noninfected.

Soil carbon dioxide and mineral accumulation in citrus seedlings (Citrus sinensis var. Bessie)

SummaryThis experiment was conducted in a greenhouse to study the influence of soil CO2 differential treatments on plant response, concentrations of nutrients in soils and plants, and total nutrients per plant (Citrus sinensis var. Bessie).Higher levels of soil CO2, applied to the roots, significantly increased the amount of dry weight per seedling, the height of seedling, and decreased the concentrations of N, P, Ca, Mg, and Mn in the tops. The dry weight of roots supplied with high soil CO2 was decreased, while the concentrations of Mg and Mn were increased. Concentrations of N, P, K, and B in the roots were also reduced due to high level of soil CO2. Only total K and Mg per plant were increased with an increased soil CO2 supply. No significant interactions were found between the soil CO2 treatments and years of experiment.

NUTRITIONAL RESPONSES AND ROOT ROT OF CITRUS LIMON AND CITRUS SINENSIS UNDER HIGH AND LOW SOIL OXYGEN SUPPLIES IN THE PRESENCE AND ABSENCE OF PHYTOPHTHORA SPP

Scions of lemon and orange were grafted on sweet orange rootstocks, Citrus sinensis Osbeck “Bessie” grown in fumigated sandy loam. After the plants were well established, half of their number were inoculated with Phytophthora parasitica Dastur and P. citrophthora (Sm. and Sm.) Leonian. Oxygen supply to the root soil environment was controlled by having sealed containers in which oxygen concentrations over the soil surface could be reduced from atmospheric oxygen (20.93 percent) by mixing nitrogen with air. Total dry weights of leaves, stems, and roots were significantly reduced by the presence of Phytophthora spp. while only dry weight of roots was significantly reduced due to low oxygen supply. Even though the dry weight of the lemon tops was greater than that of orange the vigor of the top had no effect on root growth or root rot due to Phytophthora spp. Plants in infested soil had leaves with significantly lower concentrations of P, Ca, Mn, and Fe and significantly higher concentrations of K, Na, and Cl than those from plants grown in noninfested soil. However, supplying oxygen to the root zone at concentrations less than that in air significantly reduced concentrations of N, P, K, Ca, Mg, B, and Fe in leaves. Concentrations of K, Mg, Na, Cl, Zn, and Mn in roots were decreased in the presence of Phytophthora spp., while concentrations of N, P, K, Mg, Na, and Cl in roots were decreased by low oxygen supply. There were significantly higher concentrations of N, K, Ca, Na, Cl, and B in leaves of orange than in leaves of lemon, while in roots of orange there were significantly lower concentrations of Mg, Zn, Mn, and Fe than in lemon roots.