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  • Author or Editor: Harry A. Mills x
  • Journal of the American Society for Horticultural Science x
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Abstract

A commercial formulation of 2-chloro-6-(trichloromethyl)-pyridine (nitrapyrin) was incorporated within the N-fertilizer band in 2 consecutive years under widely different environmental conditions to evaluate the effect of nitrapyrin on denitrification occurring with field-grown sweet corn (Zea mays L.). Nitrapyrin significantly increased soil NO 3–N levels, total plant N, and yield; decreased rates of N2O evolved from the soil with both NH+ 4 and NO 3 forms of N-fertilizer. Denitrification appears to be a significant factor influencing the growth of sweet corn under field conditions, and nitrapyrin effectively inhibits the denitrification process.

Open Access

Abstract

Nitrate and NH 4 + absorption by southernpeas (Vigna unguiculata (L.) Walp.) during the growth cycle was determined in solution culture at 7-day intervals. Dry weight and total mg of N for each plant part were determined at bloom initiation, pod initiation, and seed maturity. When the N concentration was deficient virtually all of the N 3 was absorbed by southernpea plants from the 3rd week until harvest. At sufficient N concentrations a single peak N 3 uptake period occurred in the growth cycle prior to bloom initiation. Nitrate absorption predominated when NH 4 + constituted 50% or more of the N form at both N concentrations. Ammonium had either 1, 2 or 3 absorption peaks depending upon its relative concentration with NO 3 . The first NH 4 + absorption peak was the largest and coincided with the growth cycle just prior to bloom initiation. Dry weight and N accumulation were greatest prior to bloom initiation. Subsequent accumulation occurred primarily in the seed. A reduction in N content and dry weight in the vegetative portions, particularly the leaves, coincided with the accumulation of N and dry weight in the seeds. Use of total mg of N in the vegetative tissue as a means of indicating the N status of the plant and subsequent yield was not accurate.

Open Access

Abstract

Use of electrostatic spray deposition for the control of insect infestation in broccoli (Brassica oleracea L., Italica group) resulted in equal or greater control in comparison to conventional methods, and utilized ½ to 1/3 the quantity of insecticide with an 8-fold reduction in application volume. Laboratory tests documented a 1.86-fold improvement in the quantity of spray tracer deposited electrostatically onto broccoli plants as compared with conventional application.

Open Access

An irrigation scheduling model for turnip (Brassica rapa L.) was validated using a line-source irrigation system in a 2-year field trial. The model used a water balance, a variable root length, and a crop factor function of plant age (i). Evapotranspiration was computed daily as class A pan evaporation times a crop factor [CF(i) = 0.365 + 0.0154i-0.00011i2]. Irrigation according to the model maintained soil water tension at <25 kPa at a 30-cm depth. When rainfall amounts were less than water use, leaf yields responded quadratically to irrigation rates, from 0% to 160% of the model rate, and the highest leaf yield with the lowest water applications corresponded to the model rate. Therefore, this model could replace the “feel or see” methods commonly used for scheduling irrigation of leafy vegetables grown in the southeastern United States.

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