In situ ion exchange resin membrane (IEM) technique to measure soil mineral nitrogen dynamics in grazed pastures

This paper explored the potential of application of in situ ion exchange resin membrane (IEM) technique for assessing soil nitrogen (N) availability and spatial distribution in New Zealand grazed pastures. Field and incubation experiments conducted to test the technique proved IEM technique to be a useful approach to monitoring the continuous changes in soil mineral N in pasture soils. The field testing showed that the IEM technique reflects both differences in pool size and mineral N flux, while 2-M KCl extraction reflects only pool size at the sampling. Testing the effects of residence time, temperature, soil inorganic N content, and soil water content through diffusion modeling offers further support for using IEM to explore the complex dynamics of nitrogen availability in pasture soils.     

Use of index selection in recurrent selection programs in maize

Summary Phenotypic and genotypic correlations were examined for four traits in seven populations of maize (Zea mays L.) undergoing recurrent selection. Correlations among grain yield and percentage of grain moisture, root lodging, and stalk lodging were low (|r|<0.3) except for the correlation between grain yield and stalk lodging, which was high and negative. The phenotypic and genotypic correlations agreed well from cycle to cycle within populations. Variation of correlations among populations was not significantly larger than variation among cycles. Heritabilities of these traits generally were high (h²>0.5). Two indices, one that used heritabilities as index weights and one that used relative economic weights (base index) as index weights, were compared with the Smith-Hazel index (optimim index). Relative efficiencies of the two indices, in terms of predicted gains for the individual traits and the composite trait, compared with the Smith-Hazel index, were high. The use of an index in which heritabilities were used as index weights was recommended because:1) the heritabilities were the same as the optimum weights when the traits were uncorrelated, and for the data examined the correlations were low; and 2) heritabilities were computed in routine data analyses and were available at no additional cost.Joint contribution: USDA-SEA-AR and Journal Paper No. 10152 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project 2194.     

Thermal oxidation of 9'-cis-neoxanthin in a model system containing peroxyacetic acid leads to the potent odorant beta-damascenone

The potent odorant beta-damascenone was formed directly from 9'-cis-neoxanthin in a model system by peroxyacetic acid oxidation and two-phase thermal degradation without the involvement of enzymatic activity. Beta-damascenone formation was heavily dependent on pH (optimum at 5.0) and temperature, occurring over the two sequential phases. The first was incubation with peroxyacetic acid at 60 degrees C for 90 min, and the second was at above 90 degrees C for 20 min. Only traces of beta-damascenone were formed on application of only one of the two phases. Formate and citrate solutions produced a much better environment for beta-damascenone formation than acetate and phosphate. About 7 microg/L beta-damascenone was formed from 5.8 mg/L 9'-cis-neoxanthin under optimal experimental condition. The detailed pathway by which beta-damascenone is formed remains to be elucidated.     

The effect of crop residue incorporation date on soil inorganic nitrogen, nitrate leaching and nitrogen mineralization

 Delaying cultivation and incorporation of arable crop residues may delay the release of NO₃ ^– and hence reduce leaching. The objective of this study was to investigate the effect of timing of cultivation on the mineralization and leaching of NO₃ ^– from an arable crop residue. Overwinter N leaching and periodic measurements of soil inorganic N were combined to estimate net N mineralized after ploughing a crop residue into a free-draining loamy sand soil in central England on six dates from June 1994 to January 1995. The crop residue was whole green barley with approximately 2% N. N leaching in the two following winters was increased by the addition of crop residues. Early residue application also tended to increase N leached in the first winter, largely as a consequence of relatively large losses early in the drainage period. Thus, early incorporation of crop residues presents a greater leaching risk. The amount of N leached in the second (drier) winter was similar for all dates of incorporation. At the end of the first winter, inorganic N derived from the crop residue was greatest for earlier additions: June (40% N applied) > September (30% N applied) > August (20% N applied) > October (19% N applied) > November (11% N applied) > January (3% N applied). However, at the end of the experiment, there was no evidence that the residues which had mineralized least by the end of the first winter had, to any significant degree, caught up, and this was confirmed by the parameters of the equation for first-order decomposition in thermal time. These results indicate that the effect of temperature, particularly in the early stages of residue mineralization, is complex and interacts with other soil processes in terms of the fate of the N mineralized. Received: 19 July 1999     

Phytoextraction Potential of Indian Mustard at Various Levels of Zinc Exposure

ABSTRACT

Indian mustard (Brassica juncea Czern.) has the potential to extract zinc (Zn) and other metals from contaminated soils, but the potential to accumulate metals at different levels of exposure is not well documented. The objectives of this research were to assess plant growth and Zn accumulation for different metal-accumulating accessions of Indian mustard grown with various Zn concentrations. In the experiment, three accessions of Indian mustard (426308, 182921, and 211000) were supplied with 12 levels of Zn (ranging from 0.0 to 7.0 mg L^?1) for three weeks in solution culture. Accession 426308 had a greater capacity for dry-mass accumulation than the others, but differences among accessions lessened as the concentration of Zn in solution increased. Accessions did not differ in Zn concentrations in shoots, but accession 426308 had a greater potential to accumulate Zn than the other accessions. Elevating the Zn supply in solutions had a limited effect on increasing the total Zn accumulation of shoots. Plants suffered Zn-induced iron (Fe) deficiency if the Zn concentration in solution exceeded 2.0 mg Zn L^?1. The level of Zn tolerance of Indian mustard accessions was: 211000 > 182921 > 426308. Maximum Zn accumulation in shoots was approximately 5.0 mg Zn per plant. The phytoextraction potential of Indian mustard may be limited under Zn-contaminated conditions by nutrient disorders and toxic effects of Zn that suppress growth.     

A Potential Solution to Mitigate Phosphorus Release Following Clearfelling in Peatland Forest Catchments

Since the 1950s, large areas of upland peat have been afforested in northern European countries. Due to the poor phosphorus (P) adsorption capacity and low hydraulic permeability in blanket peat soil and increased labile P sources, harvesting these blanket peat forests can significantly increase P concentrations in the receiving aquatic systems. This paper briefly reviews the current management practices on the control of P releases from forestry in Ireland and the UK, and proposes a possible novel practice??grass seeding clearfelled areas immediately after harvesting, which should reduce P release from blanket peat forest harvesting. The study was conducted in the Burrishoole Catchment in the west of Ireland. A field trial was carried out to identify the successful native grass species that could grow quickly in the blanket peat forest. The two successful grass species??Holcus lanatus and Agrostis capillaris??were sown in three blanket peat forest study plots with areas of 100, 360, and 660 m² immediately after harvesting. Areas without grass seeding were used as controls. One year later, the P content in the aboveground vegetation biomass of the three study plots were 2.83, 0.65, and 3.07 kg P?ha^?1, respectively, which were significantly higher than the value of 0.02 kg P?ha^?1 in the control areas. The water extractable phosphorus in the three study plots were 8.44, 9.83, and 6.04 mg?(kg dry soil)^?1, respectively, which were lower than the value of 25.72 mg?(kg dry soil)^?1 in the control sites. The results indicate that grass seeding of the peatland immediately after harvesting can quickly immobilize significant amounts of P and warrants additional research as a new Best Management Practice following harvesting in the blanket peatland forest to mitigate P release.     

Development of a crop knowledge base for Europe

This paper describes the development of a Crop Knowledge Base System for use in crop modelling and yield forecasting. The inherent limitations of databases can cause problems for dealing effectively with geo-referenced data sets. The system described here includes all the normal database operations but also handles richer types of data. Values of queried attributes can be deduced through the use of heritability within hierarchies and by the application of rules that summarise sets of empirical observations. The system is able to reason about similar locations, so that where no information exists in the knowledge base for a particular location, then an alternative location, subject to similar meteorological and agricultural conditions, will be sought.     

Allometric biomass equations for tree species used in agroforestry systems in Uganda

Estimates of above-ground biomass are required for better planning, sustainable management and monitoring of changes in carbon stocks in agroforestry systems. The objective of this study was to develop and compare biomass equations for Markhamia lutea, Casuarina equisetifolia, Maesopsis eminii and Grevillea robusta grown in a linear simultaneous agroforestry system in Uganda. These species were established in single rows in the middle of fields in 1995 from four-month old seedlings. A total of 57 trees were sampled for this study, 13 for M. lutea, 12 for C. equisetifolia, 16 for M. eminii and 16 for G. robusta. Biomass values of the various tree components (stem, branches and foliage) as well as the total above-ground biomass were fitted to linear and non-linear allometric models using total height, diameter-at-breast height (DBH), crown width as predictor variables. Although both DBH and height are typically used as independent variables for predicting above-ground biomass, the addition of height in biomass equations did not significantly improve model performance for M. eminii, M. lutea and G. robusta. However, addition of height significantly increased the proportion of variation explained in above-ground biomass for C. equisetifolia, while DBH did not significantly improve the prediction of biomass. The study confirmed the need for developing species-specific biomass equations.     

Physiological variation among western redcedar (Thuja plicata Donn ex D. Don) populations in response to short-term drought

? Variation in the ability of western redcedar (Thuja plicata Donn ex D. Don) populations to withstand water stress may exist because this species is found in coastal and interior biogeoclimatic subzones representing the full range of precipitation regimes in British Columbia, Canada.

? Seven western redcedar populations from locations in British Columbia, representing a wide range of habitat types, were assessed for their gas exchange and water relations response to controlled drought.

? Before drought, population variation occurred in stomatal conductance, net CO₂ assimilation rate and intrinsic water use efficiency and the relative water content at turgor loss point. During drought, populations had different responses of net CO₂ assimilation to decreasing predawn shoot water potential. After drought, populations differed in stomatal conductance and intrinsic water use efficiency, plus osmotic potential at turgor loss point, osmotic potential at saturation and apparent cuticular transpiration. Western redcedar populations from drier-inland habitats had a lower osmotic potential at turgor loss point, lower relative water content at turgor loss point and lower apparent cuticular transpiration in response to drought than populations from coastal origin with temperate maritime habitat.

? Reduction of cuticular water loss and adjustments of cellular water relations in response to drought was found to occur among seven western redcedar populations originating along a precipitation gradient while; there were minimal population differences in the gas exchange response to drought.