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Nitrogen fertilization is a required production practice for cotton (Gossypium hirsutum L.) with risks arising from under- and over-fertilization. Tissue testing for diagnosing N deficiencies in crops can use leaf blades and the total N concentration, but this practice has not been rigorously examined in cotton. The primary objective of these experiments was to determine the leaf-N concentration of the uppermost, fully mature leaf blade below which yield loss could be expected. Nitrogen-rate field experiments were conducted at 12 research station and farm sites in the Midsouth USA in Louisiana, Arkansas, Mississippi, and Alabama in 1996 and 1997. Leaf-blade total N concentrations associated with yield loss were 43% N at early bloom (R 2 = 0.50) and 4.1% N at mid-bloom (3 wk after early bloom, R 2 = 0.32). The likelihood of applying N when not needed could be reduced by lowering the early bloom critical value to 3.9%. Only 4% of all samples sufficient in N would have been incorrectly diagnosed N deficient at that critical value, but 44% of all deficient samples would have been misidentified as N sufficient. Reduced yields due to over application of N were evident in some samples with leaf N between 4.6 and 4.8% at early bloom These concentrations were also common for N-sufficient plants, making accurate diagnoses of the over application of N unlikely. Our leaf-N critical values probably differ from previously established values because earlier values were derived via survey techniques and because faster fruiting cultivars may require higher leaf N.

Chelator-buffered hydroponic solutions provide low and buffered free-metal concentrations and allow the easy calculation of nutrient species expected in these solutions. Some researchers suspect that the solutions allow plant uptake of chelates and that this uptake explains the failure of the free-ion activity model using these solutions. To determine the amount and method of chelate uptake, swiss chard was grown in solution culture in growth chambers for about three wks and then transferred to solutions containing 14C-EDTA, 14C-citrate, or 14C-L-histidine for a 21-hour assay. Much higher root and shoot 14C were found from treatments containing metabolites histidine (2706 097 shoot Bq 14C) or citrate (2241 953 shoot Bq 14C) than EDTA (280 110 shoot Bq 14C). Passive transpirational flow could explain all of the EDTA uptake, but active uptake would be required to explain most of the citrate and histidine uptake even assuming some adsorption of ligand bound to roots. Swiss chard grown in solutions with the same total EDTA concentrations, but different amounts of Fe bound to EDTA, had ≥3-fold differences in root and shoot 14C concentrations. In a second experiment, swiss chard roots removed more EDTA from solutions containing mostly M-EDTA0 than M-EDTA1- or M-EDTA2- (288 140, 245 051, and 192 559 Bq 14C, respectively) suggesting plant selectivity for EDTA and a non-apoplastic route of uptake or an effect resulting from root cell-wall adsorption. Results indicated buffering of metals by ligands allowed some ligand uptake with much more uptake occurring with metabolites citrate and histidine than EDTA. A passive or indiscriminate form of uptake does not appear to explain all EDTA uptake with a selectivity by swiss chard for M-EDTA complexes of lower charge.

Pearl millet [Pennisetum glaucum (R) Br.] is a promising alternative grain crop for the Southeast and mid-South regions of the USA, but additional N fertility information is needed to optimize its production. Identification of a critical tissue N level at early growth stages is necessary to determine the need for subsequent applications of N. Field experiments were conducted to determine the response of hybrid 'HGM 100' grain yield, protein yield, and shoot N concentration to N application rate and to determine the relationship of grain yield and protein yield with shoot N concentration at different growth stages. Grain yield response to N fertilizer applications from 0 to 168 kg ha -1 , in 34-kg increments, varied among five field environments ranging from sandy loam to silty clay loam soils and resulted in a moderately low correlation (r 2 = 0.36). Relative total protein yield was more consistent (r 2 = 0.67). Tissue N concentration of shoots harvested 44 ± 4 d after seeding [early boot(EB)] was related to relative grain yield (r 2 = 0.65). A critical N concentration of 31 kg -1 dry matter (dm), determined by regression and old Cate-Nelson procedures, resulted in optimum grain yield. On a per hectare basis, total relative protein yield also correlated moderately high with shoot tissue N concentration at EB (r 2 = 0.70). The use of Cate-Nelson procedures determined a critical N concentration in shoot tissue at EB of 32 g kg -1 dm. Determination of a critical N level at an earlier growth stage resulted in low correlations with yield parameters. On the basis of critical values at the EB stage, N amendments could possibly be applied in time to enhance some yield components, although the effective application window is narrow.

Nitrogen (N) is applied to golf course fairways at rates similar to that applied to corn. This appears excessive since N fertilization of corn is approximately equal to the amount of N removed at h...

A survey ofthe nutrient status ofthe citrus groves of Louisiana was conducted to determine the extent of possible deficient or toxic areas of the region and to help determine the accuracy of critical values developed in the major citrus-growing regions of the world and their relevance to a region where critical values had not been developed. The nutrient status of 29 orchards of Washington navel orange (Citrus sinensis) and satsuma mandarin (Citrus unshiu) trees on P. trifoliate rootstock representing 90% of the citrus region in Louisiana were determined using critical values from the literature. Twenty percent of survey samples ranked excessively high in chloride indicating possible toxicity from recent salt-water intrusion. Chloride contents were higher in groves closer to the Gulf of Mexico. More than 60% of the leaf samples analyzed were diagnosed as having very low concentrations of zinc (Zn) and manganese (Mn). Soil tests of surface soils to a 15-cm depth did not prove useful in predicting Zn and Mn nutrition oftrees, as all soil samples had medium or high levels of DTPA-extractable Zn and Mn. Phosphorus (P) and potassium (K) were low in more than 20% of the leaf samples and high in less than 5% of the samples. Calcium (Ca) in the young leaves was low or very low in 95% of the samples, but no samples from older leaves were low or very low in Ca. These results indicate possible transient effects, errors in the critical values used, or environmental conditions that inhibit Ca uptake.

The shoots of primary Se-accumulating plant species can accrue Se to several thousand micrograms per gram of dry weight, even when growing in gypsiferous soils, yet no detailed studies of the mutual antagonism between SeO4 and SO4 during plant uptake have been conducted with these species. In a comparative study, we grew a nonaccumulator (alfalfa, [Medicago sativa L.]) and a primary Se accumulator [Astragalus bisulcatus (Hook.) A. Gray] in identical nutrient solutions with varied SeO4 (2-80 and SO4 (0.5-15.5 mM) concentrations for 21 (alfalfa) or 32 to 35 d (A. bisulcatus). Shoot S concentrations in alfalfa were increased by increases in solution SeO4, but only when shoot Se was above 20 g, suggesting that SeO4induced stimulation of S uptake may be a result of incipient Se toxicity. Similar stimulations of S uptake were less apparent in A. bisulcatus. Alfalfa shoot Se concentrations ranged from 4 to 154 g, while the same treatments resulted in shoot levels of 175 to 1200 g 1 in A. bisulcatus. Uptake of SeO4 by alfalfa was profoundly inhibited by increases in solution SO4, while Se uptake by A. bisulcatus was much less, although still significantly, affected. Comparison of molar Se/S ratios in plants and nutrient solutions indicated discrimination against Se by alfalfa, but preferential accumulation of Se by A. bisulcatus. A reevaluation of previously published results was in general agreement with our findings, and suggested that primary Se accumulators have a unique ability to accumulate SeO4 in the face of competition from SO4. These species could thus prove useful in efforts to remediate Se-contaminated soils or sediments that are also enriched in SO4. Overall plant discrimination between SeO4 and SO4 may be related to (i) discrimination between the two analogues during initial absorption, or (ii) differential retranslocation of these elements to the root with subsequent afflux to the external solution. View complete article To view this complete article, insert Disc 5 then click button8

Tomato plants (Lycopersicum esculentum Mill.) were grown for 21-days in a complete hydroponic nutrient solution including Fe(3+)-ethylenediamine-di(o-hydroxyphenylacetate) and subsequently switched to nutrient solution withholding Fe for 8 days to induce Fe stress. The roots of Fe-stressed plants reduced chelated Fe at rates sevenfold higher than roots of plants grown under Fe-sufficient conditions. The response in intact Fe-deficient roots was localized to root hairs, which developed on secondary roots during the period of Fe stress. Plasma membranes (PM) isolated by aqueous two-phase partitioning from tomato roots grown under Fe stress exhibited a 94% increase in rates of NADH-dependent Fe(3+)-citrate reduction compared to PM isolated from roots of Fe-sufficient plants. Optimal detection of the reductase activity required the presence of detergent indicating structural latency. In contrast, NADPH-dependent Fe(3+)-citrate reduction was not significantly different in root PM isolated from Fe-deficient versus Fe-sufficient plants and proceeded at substantially lower rates than NADH-dependent reduction. Mg(2+)-ATPase activity was increased 22% in PM from roots of Fe-deficient plants compared to PM isolated from roots of Fe-sufficient plants. The results localized the increase in Fe reductase activity in roots grown under Fe stress to the PM.