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Asfaw Zelleke, George C. Martin, and John M. Labavitch


A gas chromatograph equipped with a nitrogen-phosphorus detector was used for quantitation of cytokinins. The described system, utilizing permethylated derivatives, will detect as little as 0.1 pg adenine, isopentenyl adenine, benzylamino purine, and kinetin, and 10 pg zeatin. As with all highly sensitive instrumentation, scrupulous procedures for sample preparation are essential.

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Warren E. Copes, Haibo Zhang, Patricia A. Richardson, Bruk E. Belayneh, Andrew Ristvey, John Lea-Cox, and Chuanxue Hong

, especially nitrogen (N) and phosphorus (P), associated with overflow from lakes and stormwater basins ( Burgin and Hamilton, 2007 ; Chiandet and Xenopoulos, 2016 ; Hem, 1985 ; Lea-Cox et al., 2001 ; Song et al., 2015 ). Nitrogen and phosphorus both partly

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Milton D. Taylor*, Stephen J. Klaine, and Ted Whitwell

Mitigation of offsite movement of nutrients in nursery runoff is a serious concern for commercial nurseries with container-grown plants. Wight Nurseries, Cairo, Ga. has operated 3.77 ha of planted constructed wetlands since 1996 to remediate nutrients from runoff. The wetlands receive drainage from a 48.6 ha nursery production area. Monitoring by nursery staff had suggested net export of nitrogen and phosphorus may occur during spring regeneration. Intensive monitoring was conducted between early March and mid-May 2003. There was no net export of nitrogen during the study. Nitrite nitrogen removal remained at 100% in the 1st stage wetland throughout March but declined in April to 89.6% as loading increased 5-fold. However, the 2nd stage wetland removed 100% of the remaining nitrite. Nitrate removal in the 1st stage wetland was high through early April (97.6%) but low in 2nd stage wetlands (16%) until loading increased 10-fold when efficiency rose to 94.9%. Nitrate removal by the 1st stage declined during mid-April but 2nd stage efficiency remained above 95%. For phosphorus, there was net export during March from both stages. However, during April, the wetlands removed phosphorus although loading tripled during the month. In May, net export of phosphorus from the wetlands recommenced with peak 1st stage export of 130% and 2nd stage uptake declining until mid-May when export began again. Neither water temperature nor rainfall appeared correlated with wetland efficiency. While phosphorus was exported by the wetlands during parts of the study, neither nitrate nor nitrite was exported as spring progressed and decomposition of last year's growth accelerated.

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Renae E. Moran and James R. Schupp

'Macoun'/B.9 apple (Malus ×domestica Borkh.) trees were planted in May 1998 in ± compost or ± monoammonium phosphate (MAP) for a total of four preplant treatments: 1) 90 g phosphorus (P) per tree, 2) 128 kg compost per tree, 3) 90 g P and 128 kg compost per tree, and 4) and an untreated control. MAP did not increase tree growth or yield in any year of the study. Compost increased canopy width into the sixth year after planting, and increased tree height and trunk cross-sectional area (TCA) into the seventh year. Annual yield was increased by compost in the fifth and seventh years, but not fourth or sixth year after planting. Compost increased cumulative yield in the sixth and seventh years.

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Raphael Goren, Moshe Huberman, and George C. Martin

Previous studies have demonstrated that phosphorus, which stimulates ethylene biosynthesis, induces abscission of olive leaves directly without the involvement of ethylene. In the present study this possibility was further explored by comparing the effects of an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), and an ethylene action inhibitor, 2,5-norbornadiene (NBD), in olive [Olea europaea (L.) `Manzanillo'] and citrus [Citrus sinensis (L.) Osbeck `Shamouti']. In olive, leaf abscission was always induced in the presence of KH2PO4 with or without AVG and NBD (alone or in combination), but it was much more pronounced when KH2PO4 was applied alone. In citrus, KH2PO4 did not induce leaf abscission in the presence of NBD during the first 48 (detached shoots) or 60 hours (leaf explants) despite the high levels of ethylene production by the tissues. Our results demonstrate that phosphorus can, at least partly, act independently of ethylene action in inducing leaf abscission in olive but not in citrus.

Open access

M. Awada, R. Suehisa, and Y. Kanehiro


Papaya plants, Carica papaya L. cv. Solo, were treated with 3 levels of lime combined with 3 levels of P in a split-plot arrangement. Optimal yield of papaya was maintained when the pH of the surface soil ranged from 5.5 to 6.7. Liming lowered petiole concentrations of Mn, K, and Mg and raised those of Ca and P; petiole P was raised when P was applied only. Phosphorus fertilization increased the growth rate of the tree-trunk circumference only at the early stage of growth, while liming affected growth later than P. Phosphorus fertilization raised the petiole concentrations of P, N, Mn, and Zn and lowered petiole concentrations of K and Cu.

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Hisashi Yamada and George C. Martin

The addition of Al2O3 to 8-hydroxyquinoline citrate (8-HQC) solution did not alter the sensitivity of the leaf abscission zone to external ethylene treatment. Exogenous ethylene at 791 nl·l-1 for 72 to 120h and at 193 nl·l-1 for 120h induced leaf abscission whereas at 47 nl·l-1 for 72 to 120h no leaf abscission occurred. Ethylene treatment at 791 nl·l-1 for 72 to 120h increased ethylene evolution, but the amount of ethylene evolved from the explants does not seem to be enough for leaf abscission induction. Three different ethylene inhibitors, aminooxyacetic acid (AOA), CoCl2 and am inoethoxyvinylglycine (AVG), were used to determine whether phosphorus-induced leaf abscission was mediated through elevated ethylene evolution. Although AOA and CoCl2 failed to inhibit ethylene evolution from the explants stem-fed with NaH2P O4, AVG inhibited ethylene evolution. Each of the inhibitors except for 5 mM CoCl2 promoted leaf abscission when administered alone or with phosphorus. Our results reveal that phosphorus induced olive leaf abscission occurs without elevated ethylene evolution, but that oxygen is required.

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Eric J. Biddinger, Chunming Liu, Robert J. Joly, and K.G. Raghothama

Phosphorus is one of the essential but limiting nutrients in nature. In this study, we link the physiological changes occurring under phosphate (Pi) starvation to gene expression. Roots of aeroponically grown tomato (Lycopersicon esculentum L.) plants were sprayed intermittently with nutrient solutions containing varying concentrations of P. Decreasing the concentration of Pi in the nutrient solution resulted in reduced biomass production and altered the tissue concentration of nutrients in roots and shoots. Phosphorus starvation increased the root:shoot biomass ratio and decreased net CO2 assimilation and stomatal conductance. Phosphorus concentrations in roots and shoots decreased with decreasing concentration of Pi in the nutrient solution. Pi-deficient plants had a higher concentration of Ca in roots and Mg in shoots. Expression of the Pi starvation-induced gene, TPSI1, persisted even after 3 weeks of Pi starvation. The transcript accumulation in leaves was found to be a specific response to Pi starvation and not to the indirect effects of altered N, K, Fe, Mg, or Ca status. Accumulation of transcripts was also observed in stem and petioles, suggesting a global role for TPSI1 during Pi starvation response of tomatoes.

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M.W. van Iersel, R.B. Beverly, P.A. Thomas, J.G. Latimer, and H.A. Mills

Good fertilizer management is important in plug seedling production of bedding plants to prevent nutrient deficiencies and toxicities. We determined the effect of N, P, and K nutrition on the growth of plugs of impatiens (Impatiens wallerana Hook. f.), petunia (Petunia ×hybrida Hort. Vilm.-Andr.), salvia (Salvia splendens F. Sellow ex Roem.& Schult.), and vinca (Catharanthus roseus L.). For all four species, shoot N concentration was correlated linearly with shoot dry mass of the seedlings at transplant. Phosphorus or K concentration in the nutrient solution or shoot tissue had little or no effect on the shoot growth of seedlings, but shoot P levels increased with P concentrations in the fertilizer solution (luxury consumption). Salvia was the only species that also exhibited luxury consumption of K. Results of this study indicate that seedling growth of these species is mainly determined by N and this should probably be the main focus of fertility programs in the plug industry, while P and K applications can be reduced.

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Reuben B. Beverly, Wojciech Florkowski, and John M. Ruter

In response to a mail survey of the landscape maintenance and lawn care (LM-LC) industry in metropolitan Atlanta, we learned that 76% of respondents fertilized lawns and turf and 68% fertilized ornamental beds. Less than one-fourth of those who provided fertilization services offered an organic fertility option; for those who reported an organic option, an average of 25% of their residential customers used such a service. Complete fertilizers (N-P2O5-K2O), ammonium nitrate, urea, and N solutions were the products applied by most respondents. Average amounts of N per application were ≈1.5 lb/1000 ft2 on lawns and 1.1 lb/1000 ft2 on ornamentals. Of firms that provide fertilization services, 88% use a predetermined application schedule, whereas 88% use visual observation and 69% use soil testing to guide fertilizer management. Only 5% reported using tissue analysis as a fertilizer management strategy. Nitrogen fertilizers were applied most frequently in the spring, with nearly equal amounts applied in summer and fall. Phosphorus was applied most commonly in the fall or spring. Relatively few firms reported applying significant amounts of either N or P in winter. Most respondents indicated that they received adequate information about fertilizers, but few received information about organic fertilization. Commercial sales representatives and trade magazines were cited most often as sources of information; university specialists were the least-cited formal source of information concerning fertilization. We have suggested some research and educational issues to be addressed based on these results.