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Abstract. -- The Rio Grande is a major source of water for agricultural and municipal uses in Texas and northern Mexico. Water shortages in the Rio Grande have been significantly [...]

The effects of radiata pine (Pinus radiata D. Don.) seedlings and ryegrass (Lolium perenne L.) on the mineralisation of orthophosphate monoesters in 7 grassland soils were assessed in a 10-month pot trial using NaOH-EDTA extraction and solution [sup.31]p NMR spectroscopy. Extraction with NaOH EDTA recovered 46-86% of the total soil P, and NaOH EDTA-extractable organic P determined by molybdate colourimetry ranged between 194 and 715 mg/kg soil, representing 34 85% of the total soil organic P. Orthophosphate monoesters were the predominant species of the extracted organic P in all soils, with much smaller concentrations of orthophosphate diesters, and traces of phosphonates. Concentrations of orthophosphate monoesters were consistently lower in soils under pine (103-480 mg P/kg soil) compared with the initial soils (142-598 mg P/kg soil) and most soils under grass (122-679 mg/kg soil). Mineralisation of myo-inositol hexakisphosphate accounted for 18-100% of the total mineralisation of orthophosphate monoesters in most soils under radiata pine. This suggests that supposedly recalcitrant inositol phosphates are available for uptake by radiata pine, although the extent of this varies among soils. Additional keywords: Pinus radiata, Lolium perenne, solution [sup.31]p NMR spectroscopy, myo-inositol hexakisphosphate, spectral deconvolution., Introduction Continued advances in our understanding of the chemical nature and associated dynamics of soil phosphorus (P) are important to ensure that agricultural and forest ecosystems are managed in a [...]

Abstract.--Aerial color-infrared (CIR) photography was used to detect and catalog unauthorized solid waste disposal sites around Donna Reservoir in the Lower Rio Grande Valley (LRGV) of southern Texas. Qualitative visual [...]

Afforestation of grassland provides an opportunity for partial mitigation of increasing carbon dioxide ([CO.sub.2]) levels in the atmosphere through carbon (C) fixation in biomass, but little is known of the impact of afforestation on soil C. To determine the impact of afforestation on soil C levels, data from published papers, theses, and unpublished studies of paired adjoining grassland and afforested sites in New Zealand were assembled and compared. The forest sites within each pair were planted into grassland rather than some other land use, and were a minimum of 10 years old. A total of 28 paired sites had information on both mineral soil C concentration and bulk density, 17 with the forest part of the pair aged 10-20 years, and 11 with the forest aged more than 20 years. Forest floor C information was available for 9 sites. Only 3 of the forest stands had been harvested. Results indicated that afforestation of grassland soils reduces upper mineral soil (mainly 0-10 cm layer) C levels by about 4.5 t/ha or 9.5% in the short-term; however, beyond forest age 20 years there was no difference mineral in soil C between the two systems. Soil bulk density in the 0-10 cm layer was unaffected by afforestation during the first rotation. This allowed comparison of a larger number of sites (27 with forest aged 10-20 years, 18 with forest aged >20 years) that had C concentration data only. Analysis of this larger data set confirmed results obtained from the C mass data alone. Effects of afforestation on mineral soil C were most pronounced in the upper soil and declined rapidly with depth to the extent that at most sites there was no influence of afforestation on soil C below the 0-10 cm layer. At some sites, however, the impact of afforestation proceeded to greater depths, and further study is required to determine reasons for differences between sites in this regard. The impacts of afforestation on soil C observed from the paired-site studies agree well with those of recent analyses for the upper soil layer using New Zealand national soils databases. At greater depths, however, analyses using the databases appear to greatly overestimate the influence of afforestation on soil C. The available data indicate that C accumulating in the forest floor is likely to exceed any short-term reduction in mineral soil C arising from grassland afforestation. Additional keywords: bulk density, forest floor, carbon, paired sites, afforestation, grassland., Introduction Afforestation of grassland is an important and continuing land use change in New Zealand. Approximately 440 000 ha of grassland and scrub were planted to exotic forest species (predominantly [...]