The effect of cutting frequency and nitrogen fertilizer rates on dry matter production, nitrogen uptake and herbage nitrate content.

In 3 trials with perennial ryegrass given N in the range 0-1000 kg/ha and from 3 to 28 times/yr, DM production, N uptake and NO3 content in relation to N application rates and cutting frequencies of herbage were compared. Higher N application rates increased the herbage yield more at longer growing periods than at higher cutting frequencies. N uptake was positively affected by the application rate and not or only slightly by the cutting frequency. Consistent with this, appreciably high N conc. (max. 5.4%) were found on av. in the herbage at high fertilizer N rates and frequent cutting than at lower rates and less frequent cutting (1.6%). NO3 content increased during the growing season, especially as the N application rate was higher and the growing periods longer. (Abstract retrieved from CAB Abstracts by CABI’s permission

Distribution of dry matter and nitrogen between the different plant parts in intact and depodded soyabean plants after flowering.

Soyabeans were grown in nutrient sol. in a controlled environment. 50% developed normally but the rest were depodded once a wk. During 9 wk of seed development, growth of roots, shoots, leaves and pods as well as their total percentage N was monitored by weekly harvests. In the normal plants, only the pods continued to increase in dry wt. after the 2nd harvest and the wt. of the other plant parts remained nearly constant. N in roots and stems decreased slightly during pod filling and N in the leaves decreased considerably. Increase in N in the pods was relatively greater than the increase in total dry wt. The amount of N taken up from the nutrient sol. and that redistributed between plant parts was calculated. In the depodded plants, DM continued to accumulate in all plant parts throughout the experiment including the detached pods. The amount of N also increased in all plant parts. N uptake/unit DM produced was about the same for both groups of plants. The results are discussed in relation to the hypothesis that in leguminous plants the fixation or uptake of N by the roots cannot cope with the demand of the developing pods so that the necessary withdrawal from other plants parts, especially the leaves, causes the plants to die prematurely. (Abstract retrieved from CAB Abstracts by CABI’s permission

Self-Assembly of Supramolecular Triblock Copolymer Complexes

Four different poly(tert-butoxystyrene)-b-polystyrene-b-poly(4-vinylpyridine) (PtBOS-b-PS-b-P4VP) linear triblock copolymers, with the P4VP weight fraction varying from 0.08 to 0.39, were synthesized via sequential anionic polymerization. The values of the unknown interaction parameters between styrene and tert-butoxystyrene and between tert-butoxystyrene and 4-vinylpyridine were determined from random copolymer blend miscibility studies and found to satisfy 0.031<χS,tBOS<0.034 and 0.39<χ4VP,tBOS<0.43, the latter being slightly larger than the known 0.30<χS,4VP≤0.35 value range. All triblock copolymers synthesized adopted a P4VP/PS core/shell cylindrical self-assembled morphology. From these four triblock copolymers supramolecular complexes were prepared by hydrogen bonding a stoichiometric amount of pentadecylphenol (PDP) to the P4VP blocks. Three of these complexes formed a triple lamellar ordered state with additional short length scale ordering inside the P4VP(PDP) layers. The self-assembled state of the supramolecular complex based on the triblock copolymer with the largest fraction of P4VP consisted of alternating layers of PtBOS and P4VP(PDP) layers with PS cylinders inside the latter layers. The difference in morphology between the triblock copolymers and the supramolecular complexes is due to two effects: (i) a change in effective composition and, (ii) a reduction in interfacial tension between the PS and P4VP containing domains. The small angle X-ray scattering patterns of the supramolecules systems are very temperature sensitive. A striking feature is the disappearance of the first order scattering peak of the triple lamellar state in certain temperature intervals, while the higher order peaks (including the third order) remain. This is argued to be due to the thermal sensitivity of the hydrogen bonding and thus directly related to the very nature of these systems.