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  • Author or Editor: Harry A. Mills x
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Abstract

The effectiveness of the s-triazines simazine [2-chloro-6-bis (ethylamino)-s-triazine] and atrazine [2-chloro-6-(ethylamino)-6-(isopropylamino)-s-triazine and nitrapyrin [2-chloro-6-(trichloromethyl)pyridine] in suppressing denitrification was evaluated in laboratory and greenhouse studies. Parameters used to measure suppression of denitrification were N2 and N2O evolution, soil NO3-N, and plant N (% N × dry weight). Simazine and atrazine significantly reduced N2O evolution in laboratory incubation studies, but had no effect on N2 evolution, while nitrapyrin reduced both N2 and N2O evolution. In greenhouse studies, 0.5 mg kg-1 soil of simazine and atrazine, and 2.0 mg kg-1 soil of nitrapyrin increased soil NO3-N and plant N as compared to the control. It is concluded that simazine and atrazine inhibited denitrification under greenhouse and laboratory conditions and, therefore, that increased media NO3-N availability is the most likely explanation why N concentration in the plant tissue was higher.

Open Access

As a result of long-term application, some fungicides may accumulate in the soil to levels that can affect soil N transformations and plant growth. Studies were initiated to compare benomyl, captan, and lime-sulfur fungicides with the biological nitrification inhibitors (NI) nitrapyrin and terrazole for their effects on biological nitrification and denitrification, and tomato (Lycopersicon esculentum Mill.) growth and N uptake. In laboratory studies, inhibition of nitrification was less than 5% in a Tifton l.s. soil incubated with 10 μg g -1 a.i. of benomyl but was about 51%, 72%, and more than 85% when amended with lime-sulfur, captan, and NI, respectively. Similarly, increased inhibitory effects on denitrification of NO3 were obtained in a liquid media incubated anaerobically with either NI (37%) than captan or lime-sulfur (25%) while benomyl had no significant effect. In greenhouse studies with tomato plants, weekly drench applications of 0.25 μg a.i. g -1 soil of the appropriate chemical for 4 weeks with three NH4:NO3 ratios showed that the NI and captan produced the greatest plant biomass and N uptake, but benomyl and lime-sulfur had no main effect while all fungicides interacted with the N ratio to affect plant growth and N uptake.

Free access

Abstract

Consumption of spinach (Spinacia oleracea L.) with high NO3-N contents may be a health hazard to infants. Spinach leaves accumulate NO3-N when the plants are grown in a soil with high NO3-N availability. Experiments designed to evaluate the influence of nitrapyrin, a nitrification suppressor (2-chloro-6-(trichloromethyl)pyridine), on NO3-N concentrations in ‘America’ spinach and to develop a means of fertilization for maximum growth and minimum NO3-N levels in spinach were conducted. Nitrate accumulation in whole leaves and leaf fresh weights were lower with (NH4)2SO4 fertilization than with KNO3 fertilization. Nitrapyrin caused a further depression of NO3-N concentrations and plant growth with (NH4)2SO4 but had no effect on NO3-N accumulation and little effect on yield of plants fertilized with KNO3. The lesser growth with (NH4)2SO4 was apparently due to NH4-N toxicity. When half of the N was supplied as NH4-N and half as NO3-N, growth was equivalent to that of plants receiving only NO3-N, and NO3-N accumulation in the leaves was reduced by 35% without nitrapyrin and by over 50% with nitrapyrin. With this fertilizer combination, no toxicity to plant growth resulted from nitrapyrin applied at its recommended rate.

Open Access

Abstract

Tomato (Lycopersicon esculentum Mill. ‘Floradel’) plants were grown under greenhouse conditions in a modified Hoagland’s solution to determine the influence of NO3:NH4 ratio (100:0, 75:25, 50:50, 25:75) on vegetative growth, fruit development, and tissue levels of N, P, K, Ca, and Mg at 3 stages of maturity. Vegetative growth prior to fruit set was increased significantly by adding 25% of the N as NH4, although higher NH4 ratios reduced vegetative growth. During flower and fruit development, the number of fruit formed with each flower cluster was not influenced by the NO3:NO4 ratio, although fruit weights were reduced significantly when NH4 supplied any part of the N form. With each increment of NH4 in the N ratio, tissue P increased whereas K, Ca, and Mg decreased. Kjeldahl N (less NO3-N) in the vegetative tissue at all harvests increased with each increment of NH4 in the N ratio. It is concluded that the use of Kjeldahl N as an indicator of the N status of the plant without consideration of the effect of N form on the percentage of N as well as the uptake and distribution of other essential elements could be misleading and potentially a misuse of this diagnostic tool.

Open Access

Abstract

Eighteen spinach cultivars were found to vary considerably in NO3 concentrations in their leaves. Smooth-leafed cultivars were lower in NO3 concentration than heavily savoyed cultivars. Some medium or semisavoyed cultivars were low NO3 accumulators, and others were high accumulators. A low degree of savoyedness appears to be a useful factor in the selection of spinach cultivars with tendencies for low NO3 accumulation.

Open Access

Tomatillo (Physalis ixocarpa Brot. ex Hornem) is a popular crop in Mexico and other Latin American countries. There is an increasing demand for this vegetable in the United States, particularly from the growing Latino population. However, there is limited information about tomatillo production. The objectives of this study were to determine the effects of plastic mulches on plant growth, yield, and root zone temperature in two cultivars of tomatillo. The study was conducted in Spring and Summer 2000. The design was a randomized complete block with a split plot arrangement, where plastic film mulch (black, gray, and silver mulches, and bare soil) was the main plot and cultivar (`Toma Verde' and `Verde Puebla]) the subplot. In the spring, mulch treatments had little effect on plant growth during the first 30 days after transplanting and there were no significant differences in fruit yields. In the summer planting, both early growth and fruit yields were greatest with the silver and gray mulch treatments and lowest on bare soil. Plant growth during the establishment was related with subsequent plant growth and yield. In mature plants, vegetative top fresh weight and total fruit yield were higher (P < 0.01) in the spring than in the summer. Total fruit yield (both seasons), marketable yield (spring) and cull yield (spring) were lower in `Toma Verde' than in `Verde Puebla'. Root zone temperatures (RZTs) in the spring (mean = 26.4 °C) were lower than in the summer (mean = 29.3 °C). In both seasons, mean RZT was highest under black mulch and lowest in bare soil. In the summer, plant growth and fruit yields tended to decrease with increasing RZTs. Tomatillo plants grown on mulches with a mean seasonal RZT of 30 °C had fruit yields that were 65% (`Toma Verde') or 50% (`Verde Puebla') lower respectively than those of plants on mulches with a RZT of 27 °C. There were no significant differences in foliar concentrations of N, Ca, Mg, S, B, Zn, Cu and Na among mulches. Foliar concentrations of the majority of mineral nutrients were not related with the mean RZT for the season.

Free access

Ilex crenata `Helleri' (Helleri holly) can experience landscape establishment problems in the Southeast. Since aluminum toxicity is a major problem in acid soils of the Southeast, this experiment studied the effects of aluminum on Helleri holly grown in solution culture. A modified Hoagland's solution contained low phosphorus concentrations (32 μM), a 1:1 NH4+:NO3 - nitrogen ratio, and aluminum treatments consisting of 0, 222, 444, 889, and 1332 μM Al supplied at equal ratios from AlCl3·6H2O and Al2(SO4)3·18H2O. The MINTEQA2 (version 3.11) chemical speciation model was used to predict activity of ions in solution. Shoot growth and root length were not affected by aluminum after 12 weeks in solution culture. Total plant nutrient uptake was monitored weekly. Results indicate that Helleri holly does not take up aluminum ions even though NH4 + is the preferred nitrogen source. Other studies have shown increased aluminum toxicity effects when NH4 + is the preferred nitrogen source.

Free access

Ilex crenata `Helleri' (Helleri holly) can experience landscape establishment problems in the Southeast. Since aluminum toxicity is a major problem in acid soils of the Southeast, this experiment studied the effects of aluminum on Helleri holly grown in solution culture. A modified Hoagland's solution contained low phosphorus concentrations (32 μm), a 1:1 NH4 +:NO3 - nitrogen ratio, and aluminum treatments consisting of 0, 222, 444, 889, and 1332 μm Al supplied at equal ratios from AlCl3·6H2O and Al2(SO4)3·18H2O. The MINTEQA2 (version 3.11) chemical speciation model was used to predict activity of ions in solution. Shoot growth and root length were not affected by aluminum after 12 weeks in solution culture. Total plant nutrient uptake was monitored weekly. Preliminary results suggest that Helleri holly does not take up aluminum ions even though NH4 + is the preferred nitrogen source. Other studies have shown increased aluminum toxicity effects when NH4 + uptake exceeded NO3 - uptake.

Free access