Doyle A. Smittle

A comparison of analytical methods for nitrogen analysis in plant tissues

Abstract Automated Dumas methods could replace Kjeldahl digestions for the analysis of nitrogen (N), but few comparisons of these methods for plant tissue are available. Because N nutrition usually affects tissue levels of N, the influence of analytical method (Dumas and a modified micro‐Kjeldahl without salicylic acid pre‐treatment) on N determination in leaves and petioles of ‘Shogoin’ turnips grown under different N regimes was investigated. Dumas‐ and Kjeldahl‐N ranged from 1.31 to 6.70% and 1.22 to 5.77% in leaves and petioles, respectively, and Dumas‐N was significantly (p<0.01) higher than Kjeldahl‐N. This resulted in a tendency to overrate N status when available thresholds developed with Kjeldahl‐N values were use with Dumas‐N data. However, for turnip, Kjeldahl‐N could be estimated from Dumas‐N in the 1–6% range as: Kjeldahl‐N = ‐0.015 (p=0.82) + 0.858 (p<0.001) Dumas‐N (p<0.01, R2 = 0.98) , and developing new interpretative data for Dumas N was not necessary.

Ammonium reduces growth, fruit yield and fruit quality of watermelon

Abstract Watermelon (Citrullus lunatus Thunb.) plants cv ‘Sugar Baby’ were grown hydroponically in a greenhouse under NO3:NH4 ratios of 3:1, 1:1, and 1:3. Plants receiving the high ammonium treatment expressed symptoms of NH4‐toxicity and declined rapidly after bloom. Reducing NO3:NH4 from 3:1 to 1:1 significantly reduced growth, water use, fruit yield, flesh soluble solids and uptake of NO3, NH4, K, Ca and Mg.

Influence of catalyst, sample weight, and digestion conditions on Kjeldahl nitrogen

Abstract The influence of catalyst (containing K2SO4/Cu/Ti, K2SO4/Se or Se alone), sample weight (0.2 or 0.4 g), and digestion blocks (Tecator DS 1015–20 or Tecator DS 1016‐ 40) on the Kjeldahl‐nitrogen (N) determination in pecan, corn, and turnip leaves was evaluated. Mean Kjeldahl‐N values were 1.84, 2.43, and 3.72 % for the pecan, corn, and turnip samples, respectively, which were significantly higher ( = 0.05) using K2SO4/Se as a catalyst, a 0.4 g aliquot of the sample, and a DS 1015–20 digestion block. The magnitude of the differences due to catalyst, sample weight, or digestion conditions did not affect the N diagnosis status when applying interpretative data for the selected crops. The higher standard deviation (SD) for the turnip leaves compared to the pecan or corn leaves may be due to a higher nitrate (NO3) level in the turnip leaves. Selected catalyst, sample weight, and digestion conditions did not affect the SD, and therefore any combination of these factors could be used to determine Kjeldah...

Turnip growth, leaf yield, and leaf nutrient composition responses to nitrogen forms

Abstract ’Shogoin’ turnip plants (Brassica rapa L.) were grown in sand culture under five nitrate:ammonium (NO3:NH4) ratios (N:N of 1:0, 3:1, 1:1, 1:3, 0:1). The leaves expressed symptoms of NH4 toxicity (reduced growth and curly leaves with dark‐green areas surrounding yellow spots) when NH4 was the dominant nitrogen (N) form. Increasing NO3 in the nutrient solution significantly (p<0.01) increased leaf and root fresh weight and dry weight. Leaf nutrient concentration and composition of all elements analyzed, except N and calcium (Ca), responded quadratically (p<0.01) to NO3:NH4 ratios, and the highest values were observed with the 1:0 [for molybdenum (Mo)], 3:1 ([or magnesium (Mg)], 1:1 [for boron (B), coper (Cu), iron (Fe), manganese (Mn ), and zinc (Zn)] or 1:3 [for phosphorus (P) and potassium (K)] treatments. Nitrogen and Ca leaf concentration responses were linear and highest at 0:1 and at 1:0, respectively. Cultural practices and fertilizer applications should maintain NO3 as the dominant N form i...

Influence of irrigation on dry matter production, leaf composition, and nutrient removal by turnip

Abstract Irrigation scheduling of leafy greens generally consists of applying 19 mm of water every four days, which leads to irrigation depths that exceed the soil water deficit, and requires fertilizer applications higher than recommended rates. We determined the influence of irrigation scheduled by class A pan evaporation and a variable crop factor on leaf tissue composition and nutrient removal by turnips using a continuous moisture gradient and different N fertilizer conditions. Irrigation maintained foliar concentrations of N, P, K, Ca, and Mg in the sufficiency range. During dry periods, increasing irrigation increased P, decreased Mg, and had little effect on N, Ca, or K foliar concentrations. Micro‐nutrient concentrations in the leaves responded to irrigation rates, but within a narrow range. Excessive water applications, due to rainfall or to irrigation rates higher than the model rate, consistently reduced nutrient crop removal. Since a combination of water applications that did not exceed soil ...

Effects of nitrogen fertilization method and tillage system on squash growth, nutrient uptake and fruit yield

Abstract Squash, cv Dixie, grown on a Lakeland sand was subjected to factorial combinations of 3 tillage systems and 2 N application methods during 1979 and 1980. Fruit yield was greatest with a combination of moldboard plow tillage and application of 22 kg N/ha preplant and 18 kg/ha increments of N by fertigation 2, 3, 4, 5 and 6 weeks after planting. Plant growth and nutrient uptake were greatest and N available for potential contamination of the ground‐water was least with subsoil‐bed tillage and N application by fertigation. Disc harrow tillage with 67 kg N/ha preplant and 45 kg N/ha 4 weeks after planting resulted in 42% less yield, 61% less plant growth, 29 to 64% less nutrient uptake and more than 5 times as much N available for potential contamination of the groundwater as the best practices.