Harry A. Mills

Could the Dumas Method Replace the Kjeldahl Digestion for Nitrogen and Crude Protein Determinations in Foods

Increased demand for determinations of nitrogen (N), and hence crude protein (CP), has led to wider use of the Dumas method in place of the traditional Kjeldahl methods. Although Kjeldahl N (KN) and Dumas N (DN) represent different N fractions, published studies on infant formula, animal feed and meat products have indicated that DN could replace KN with little practical impact on the reliability of the N values obtained. This study was conducted to establish whether DN determination could replace that of KN in a broader range of foods for CP calculation. Statistical analysis was performed on in-house assayed KN and DN values together with published KN and DN values for selected food products. In the range 0.05-6.8% N, KN may be estimated from DN with the equation : KN = 1.00 (P<0.01) x DN - 0.09 (P=0.50) (n = 101, R 2 = 0.98, P-regression < 0.01). Because N levels in individual groups of food did not span the entire range of N contents, KN : DN ratios were calculated for each food group. KN : DN ratios differed significantly (R 2 = 0.25, P <0.01) from group to group. Ratios of 1.01 for dairy, 1.00 for oilseeds, 0.99 for feed, 0.98 for infant formulas, 0.95 for cereals, 0.94 for meats, 0.89 for vegetables, 0.80 for fish and 0.73 for fruits were valid for the estimation of KN and CP using DN data. CP was independently calculated as CP1 = H x KN or CP2 = H x KN : DN x DN, where H is the nitrogen to protein conversion factor for the food group. Mean differences between CPI and CP2 values were 0% for dairy, oilseeds, feed, infant formulas and baby foods, cereals, meat and meat products, vegetables and vegetable products and fruit, and 1% for fish. These results suggest that DN may replace KN for the determination of N and CP in selected food groups when appropriate coefficients are used.

Nutrient deficiencies and toxicities in plants: nitrogen

Current literature review and discussion of the N status of plants as related to their growth and yield and quality of produced product.

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.

Effect of nitrogen form during the flowering period on zucchini squash growth and nutrient element uptake

Abstract Zucchini squash (Cucurbita pepo L. cv. Green Magic) plants were grown hydroponically with nitrate (NO3):ammonium (NH4) ratio of 3:1 until the onset of flowering when the plants were assigned to four NO3:NH4 ratio (1:0, 1:1, 1:3, or 3:1) treatments. Changing the original nitrogen (N) form ratio significantly affected plant growth, fruit yield, nutrient element, and water uptake. Growth of plants was better when NO3‐N (1:0) was the sole form of N than when NH4‐N was part of the N treatment. Fruit yields for plants fertilized with 1:0 or 1:3 N‐form ratio were double those of plants grown continuously with 3:1 N ratio. The largest leaf area and plant water use were obtained with 1:0 N ratio treatment Total uptake of calcium (Ca), magnesium (Mg), and potassium (K) decreased with increasing NH4‐N proportion in the nutrient solution which suggest NH4‐N was competing with these cations for uptake. The results also demonstrated that growers may increase fruit yield by using a predominantly NO3‐N source fe...

STUDIES ON THE EFFECT OF ZINC SUPPLY ON GROWTH AND NUTRIENT UPTAKE IN PECAN

ABSTRACT Zinc (Zn) deficiency is a nutrient disorder observed in pecan (Carya illinoinensis Wangenh. K. Koch) under field conditions, and can cause distorted leaf growth and severe rosetting of shoots. Conducting Zn studies with pecan in the field have been problematic because Zn nutrition is difficult to control. In this study, Zn nutrient disorders were induced in greenhouse-grown pecan seedlings using hydroponic culture. Zinc efficiency was compared in two pecan seedstocks, ‘Stuart’ and ‘Curtis’ by evaluating growth response, nutrient uptake, and leaf nutrient analysis. Zinc deficiency symptoms appeared in plants grown in the absence of Zn after six weeks. Deficiency symptoms were characterized by interveinal mottling, followed by interveinal chlorosis, interveinal necrosis, and marginal curling. Symptoms were confined to the youngest most distal three to five leaves. Differences in Zn efficiency between the two seedstock were observed. “Stuart” exhibited more severe deficiency ratings than “Curtis”. Zinc supply also had a differential effect on the foliar concentration and content of Zn and other nutrient. “Stuart” seedstocks grown under minus Zn vs. plus Zn conditions exhibited significantly higher foliar concentration of phosphorus (P), calcium (Ca), magnesium (Mg), and copper (Cu), while “Curtis” leaves contained significantly higher manganese (Mn) and lower sulfur (S). Results of this study concur with the observed frequency of Zn deficiencies of the cultivars in the field, i.e., “Stuart” shows Zn deficiency more frequently then “Curtis”. This study verifies that in pecan, there are genotypic differences in Zn efficiency, and that hydroponic culture can be utilized for screening and selection.

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.

Nutrient Accumulation in Leaf Tissue of Rapid-cycling Brassuca Oleracea Responds to Increasing Sodium Selenate Concentrations

Abstract Brassica oleracea L. are important economic vegetables, and are capable of selenium (Se) enrichment to enhance human nutrition and health. Because Se enrichment may influence the nutrient balance of this crop, a study was done to test the effects of selenate‐Se on plant nutrients. Plants of a rapid‐cycling B. oleracea population were grown in nutrient solutions amended with Na2SeO4at 0.0, 3.0, 6.0, and 9.0 mg L‐1. Leaf tissue was then analyzed for nutrient content. Boron (B) (P=0.01), iron (Fe) (P=0.01), and phosphorus (P) (P=0.01) content decreased, while Se (P=0.01), sulfur (S) (P=0.01), and potassium (K) content (P=0.01) increased with increasing selenate‐Se treatments. Significant quadratic responses were found for magnesium (P=0.01) and molybdenum (P=0.01). No significant differences in leaf fresh or dry weight were detected. Changes in plant nutrient content can be expected when Brassicas are enhanced for delivery of beneficial organic Se.

Poinsettia growth, tissue nutrient concentration, and nutrient uptake as influenced by nitrogen form and stage of growth

Abstract Growth, development, and uptake of essential nutrients as influenced by nitrogen (N) form and growth stage was evaluated for ‘Freedom’ poinsettias (Euphorbia pulcherrima Willd. Ex Klotz.). Treatments consisted of five nitrate (NH4 +):ammonium (NO3 ‐) ratios (% NH4 +:% NO3 ‐) of 100:0, 75:25, 50:50, 25:75, and 0:100 with a total N concentration of 150 mg L‐1. Plants were grown in solution culture for ten weeks under greenhouse conditions. Nutrient uptake data was combined into three physiological growth stages. Growth stage I (GSI) included early vegetative growth (long days). Growth stage II (GSII) began at floral induction and leaf and bract expansion (short days). Growth stage III (GSIII) was from visible bud through anthesis and harvest. Dry weights for all plant parts and height increased as the ratio of NO3 ‐ increased. Leaf area and bract area were maximized with 25:75 and 50:50 N treatments, respectively. Nitrogen treatments significantly affected foliar nutrient concentrations with calciu...

STUDIES ON EFFECTS OF NITROGEN FORM ON GROWTH, DEVELOPMENT, AND NUTRIENT UPTAKE IN PECAN

Leaf nutrient analysis coupled with fertilizer applications are routinely used in commercial pecan production. Nitrogen can be applied in a range of formulations. However, definitive studies to establish nitrogen (N) uptake preference in pecan are lacking, as are definitive studies on the effects of N form on plant biomass production. In this study, we evaluated the effects of N form on plant growth and nutrient uptake in pecan (Carya illinoinensis Wangenh. K. Koch) using hydroponic cultures. Plants were grown under three N ratios of ammonium:nitrate (25 : 75, 50 : 50, and 75 : 25). Results from this study indicate that in-_creasing ammonium nutrition inhibited seedling growth. Plants grown with the 75 : 25 ratio (ammonium:nitrate) exhibited sig-_nificantly lower biomass, decreased root/shoot ratio, and lower specific leaf weight than observed in the other treatments. The highest root growth was observed in the 50 : 50 ratio treatment (ammonium:nitrate). Levels of calcium (Ca), magnesium (Mg), and manganese (Mn) in leaves were higher in plants grown under 25 : 75 (ammonium:nitrate) than in 75 : 25. Total N uptake on a dry weight basis was highest in the 75 : 25 ammonium:nitrate treatment. Plants exhibited preferential uptake of ammonium nitrogen under all nitrogen regimes. Ammonium nitrogen is generally applied in pecan orchard practices. This data suggest that further studies evaluating the effects of nitrogen form are warranted to determine if similar detrimental effects on pecan growth occur in the field. Such studies would be useful for optimizing current fertilization practices.

Influence of Nitrate:Ammonium Ratios on Growth and Elemental Concentration in Two Azalea Cultivars

Abstract Rooted cuttings of Rhododendron canescens “Brook” and Rhododendron austrinum were grown in sand culture with a modified Hoaglands solution under greenhouse conditions. The effect of varying ammonium:nitrate (NO3 −:NH4 +) ratios (100:0, 75:25, 50:50, 25:75, 0:100) on growth, chlorophyll content, plant quality, and elemental tissue concentration were determined. With NO3 − as the nitrogen (N) form, both azalea cultivars exhibited less vegetative growth, lower overall plant quality, with leaves showing visual chlorotic symptoms in comparison to plants receiving NH4 + as the N‐form. Leachate pH was highest with NO3 − as the predominate N‐form and decreased significantly with each increment of NH4 +. With both azalea cultivars, N‐form significantly influenced uptake and utilization of essential plant nutrients. Leaf concentrations of N, potassium (K), calcium (Ca), sulfur (S), boron (B), and molybdenum (Mo) were highest with NO3 −‐N. Leaf elemental concentrations of phosphorous (P), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) increased as NH4 + supplied more of the N‐ratio. Significant differences in Mg, Mn, and Zn were observed between species. Results from this study show that foliar N concentration is not an accurate indicator of plant growth response. Further investigations are needed to determine if foliarchlorosis and low growth rates observed with NO3 − fed plants due to an Fe deficiency, to low nitrate reductase (NR) activity in the leaves, or to a combination of these factors.