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- Author or Editor: Peter L. Minotti x
Abstract
Sand culture experiments showed that lambsquarters (Chenopodium album L.) required greater amounts of K in the nutrient media for optimum growth than did tomato (Lycopersicon esculentum Mill.). When grown in competition, the ratio of tomato to lambsquarters decreased with increasing K level in the media. At all 5 K levels employed, lambsquarter shoots contained a greater percentage of dry matter and a greater K concentration than did tomato shoots. Optimum growth for lambsquarter required shoot K concentration twice as high as tomato. In contrast to shoots, lambsquarter roots had a higher concentration of K only at lower media K levels while tomato roots had a higher concentration of K at higher K levels. Total K accumulation per unit of root mass was greater for lambsquarters at lower K levels but equal for the species at high K levels.
Abstract
Seedlings of tomato (Lycopersicon esculentum Mill.) (15 to 22 days old) exposed to unbuffered solutions containing N solely in the NH4 form showed poorly developed, thickened, less branched, discolored root systems, marginal necrosis of some leaves, wilting, particularly dark green foliage, and restricted growth. Calcium carbonate at 0.5 g/liter alleviated NH4 toxicity and restricted the accumulation of free NH4 in roots, bleeding sap, and shoots even though NH4 uptake rates were accelerated by CaCO3. Thus, the beneficial effect was related to enhanced NH4 assimilation. Roots contained an active NADH-specific L-glutamate dehydrogenase, but in vitro activity was correlated with internal NH4 content and, therefore, did not reflect actual NH4 assimilation rates during experimental periods.
Experiments were conducted at Freeville, NY and Riverhead, NY with 0-280 kg/ha of N banded. Tissue samples (both petioles and whole leaves) were taken 5 times starting 32 days from planting. There was a marked increase in yield and specific gravity from the first 112 kg/ha of N and in most cases from an additional 56 kg/ha of N. Both petiole and whole leaf nitrate were sensitive to changes in fertilizer rate that resulted in yield changes. We were encouraged by results obtained with “quick” tests on fresh sap since the pattern paralleled that obtained with traditional lab analysis of dried ground petioles. Although nitrate concentrations did not vary markedly across the varieties used there were substantial differences due to location even when the yield response curve was similar. Rate of N for rate of N, the Freeville samples were substantially higher in nitrate than those from Long Island, except at the 0 N rate, suggesting that the difference is not due to soil residual N.
Abstract
Various postharvest temperature-time combinations on nitrate-nitrite conversion in fresh spinach (Spinacia oleracea L.) were investigated. At 0°C spinach could be held as long as 40 days without significant changes in these nitrogen components. Substantial loss of nitrate-N and accumulation of nitrite-N occurred in spinach held for 3 to 7 days at 20°. Simulated transit periods of 2 weeks at 0 and 5° and simulated marketing periods of 3 days at 10° were imposed separately and in sequence to spinach in pretransit storage for 15 hours at 21° or to spinach without a pretransit storage period. Accumulations of nitrite-N exceeding 2 ppm fresh weight were found only if the simulated transit period was 5°. In this instance pre- and posttransit storage further increased nitrite accumulation. Nitrite-N levels exceeding 10 ppm were found only in visibly decayed samples.
Abstract
Tomatoes (Lycopersicon esculentum Mill.) were sampled for laboratory analysis of nitrate nitrogen (NO3-N) in one greenhouse and four field experiments. A ratio of about 3:1 (petiole NO3-N to whole leaf NO3-N) was found over a wide range of conditions for the third leaf below the growing tip and leaves further below this point. The ratio was higher for the very youngest leaves. Nitrate-N increased with leaf age and then remained relatively constant. Whole leaves proved just as effective as petioles for reflecting changes in available N.