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- Author or Editor: H.A. Mills x
Suppression of denitrification with multiple, banded applications of nitrapyrin totaling 206 g/ha increased N percentage in plants and yield of field-grown sweet corn. Lower (41 g/ha) concentration of banded nitrapyrin and all broadcast applications of nitrapyrin did not increase N percentage or yield consistently.
Responses of two hydroponically grown marigold species, Tagetes erects L. `pumpkin Crush' and T. patula L. `Janie Yellow', to Mn concentrations of 0.5 mg·liter-1 or 10 mg·liter-1 with KNO3 and Ca(NO3)2 (NO3 source) or NH4N O3 as the N source were investigated. In both species, Mn uptake was enhanced with the NO3 source while reduced with NH4NO3. With Mn supplied at 0.5 mg·liter-1 and NO3 as the N source, T. erects absorbed twice the Mn per gram of dry matter as T. patula. T. erecta accumulated higher concentration of Mn in the shoot than in the root irrespective of the N source. T. patula accumulated higher concentration of Mn in the roots with the NO3 source while NH4NO3 shifted the Mn accumulation to the shoot. Growth of both species was suppressed with 10 mg Mn/liter and the suppression was greater with the NO3 source than with the NH4NO3. These results indicate an interspecific response to Mn concentration as well as an N source influence on the uptake of Mn in marigold grown under hydroponic conditions.
Nitrapyrin at 50 ppm, increased dry weights of tomato (Lycopersicon esculentum Mill.) and total N when pine bark comprised part of the medium and NH4 was part of the N treatment. If the medium consisted only of pine bark, nitrapyrin increased dry weights and total plant N with NO3–N and/or NH4–N treatments. The NO3–N level in the medium was higher with all N treatments when nitrapyrin was incorporated. The increase in plant growth is directly related to the higher NO3–N levels in each medium where nitrapyrin was incorporated. The higher media NO3–N with nitrapyrin are attributed to inhibition of the nitrification process and a subsequent inhibitory effect on NO3–N loss.
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.
A shift in the form of Ν in the nutrient solution to all NH4 after initial bloom significantly reduced pod yield as much as 50%, depending on the prebloom NO3/NH4 ratio. Pod yield was unaffected by prebloom NO3/NH4 ratio if at least half of the Ν in the nutrient solution was NO3, or if NO3 supplied all of the Ν during postbloom development. Therefore, for maximum pod yield, NO3 should be the primary Ν form supplied to snapbean plants after bloom. Kjeldahl Ν values were consistently high in the vegetative tissue with NH4 as the predominant Ν form, indicating that the use of Kjeldahl Ν values as an indicator of the Ν status of the plant in relationship to pod yield would be a misuse of this diagnostic tool without knowing the predominant Ν form being absorbed by the plant. The NO3 content in upper mature leaves at pod maturity was significantly correlated (r = 0.88***) to NO3 level applied, with a value of 7000 ppm in the leaves associated with highest pod yield. Total Ν (Kjeldahl Ν + NO3) of at least 5.50% in upper mature leaves at pod maturity was associated with highest pod yield.
The effect of N source (
With recent advances in N analyzers, the Dumas method becomes more attractive as a replacement for Kjeldahl N. Kjeldahl N (K_N):Dumas N (D_N) ratios were determined for anthurium (A), orchid (O), fern (F) and turf (T). Dry tissues were ground to pass a 20-mesh seive. D_N was determined using 0.2 g of sample and a Leco FP-428. K_N was determined by digesting 0.4 g tissue with a CuO/TiO/K2SO4 catalyst and 10 mL H2SO4 at 450°C for 2 hr. Ammonium in the digest was assayed by colorimetry (Lachat analyzer). Overall (n=397 obs.), D_N was a good estimator of K_N: K_N = 0.90(p<0.01) D_N + 0.09(p=0.03), R2=0.93, over the 0.4-6.6 N range. K_N:D_N ratio was significantly (p<0.01) affected by plant type. Ratios of 0.85 for A, 0.92 for T, 0.99 for O, and 1.00 for F may be used to estimate K-N from D-N for the diagnosis of N nutrition, along with existing interpretative data.
Yields of `Granex 33' and `Behairy' onions (Allium cepa) closely correlated with the weight of the seeds used to establish the stand. Elemental content was consistently higher in heavier seeds, but elemental concentrations in the seeds were generally negatively related to seed weight, onion growth, and yield. A combined size-aspiration grading was an effective means of eliminating seed with low-yield potential.
Nitrogen applied as NH4-N or NO3-N (75 mg·liter-1) affected onion (AIlium cepa L.) plant growth when grown in solution culture. Nitrate alone or in combination with NH4-N increased leaf fresh and dry weight, leaf area, root fresh and dry weight, and bulb dry weight when compared to growth with NH4-N as the sole N source. Bulb fresh weight was highest with an NH4-N: NO3-N ratio between 1:3 and 3:1. Maximum leaf fresh weight was not necessary to produce maximum bulb fresh weight when onions were subjected to different N-form ratios. Precocious bulbing resulted when NH4-N was the sole N source; however, high bulbing ratios early in plant development were not correlated with final bulb fresh weight. Nitrogen form also influenced water uptake and pungency, as measured by enzymatically developed pyruvate concentration, but did not affect bulb sugar concentration.