Showing papers by "Philip C. Brookes published in 2000"

Development of an Indicator for Risk of Phosphorus Leaching

Abstract: Previous work showed that at soil P concentrations below 57 mg 0.5 M NaHCO 3 -extractable P (Olsen P) kg -1 soil, little P was found in drainage waters collected from tile drains set 65 cm below the soil surface in soils from the Broadbalk Continuous Wheat Experiment. Above this soil P concentration (termed the Change-Point) both total P and molybdate-reactive P (MRP) in drainage waters were linearly related to soil Olsen P concentrations. We now need to know if the Change-Point measured on Broadbalk occurs on other soils, and if so, whether a common value applies or if it varies depending upon soil type, management, and site hydrology. We investigated the possibility of 0.01 M CaCl 2 -extractable P being an indicator of the Change-Point. In all the soils studied, we found that the dynamics of P solubility in CaCl 2 dosely resembled the dynamics of P solubility in drainage waters of Broadbalk, since very distinct Change-Points occurred under both conditions. However, Change-Points measured following extraction with CaCl 2 varied widely between soils, from 10 to 119 mg Olsen P kg -1 soil. Lysimeter studies showed, with some exceptions, good agreement between Change-Points measured in drainage water and in 0.01 M CaCl 2 . We therefore suggest that this approach may provide a valid indicator of the soil Olsen P concentration at which significant amounts of P begin to leach from soil to water, provided preferential pathways exist in the subsoil to permit P leaching down the soil profile in drainage water.

Temperature changes and the ATP concentration of the soil microbial biomass.

Abstract: Two soils from temperate sites (UK; arable and grassland) were incubated aerobically at 0, 5, 15 or 25°C for up to 23 days. During this period both soils were analysed for soil microbial biomass carbon (biomass C) and adenosine 5′ triphosphate contents (ATP). Biomass C did not change significantly in either soil at any temperature throughout, except during days 0 to 1 in the grassland soil. Soil ATP contents increased slowly throughout the 23 days of incubation, from 2.2 to a maximum of 3.1 nmol ATP g −1 soil in the arable soil (a 40% increase) and from 6.2 to a maximum of 11.2 nmol ATP g −1 soil in the grassland soil (an increase of 81%), both at 25°C. Since biomass C did not change either with increasing temperature or increasing time of incubation, it was concluded that an increase in ATP was either due to an increase in adenylate energy charge or de novo synthesis of ATP, or both. During the incubation, biomass ATP concentrations ranged from about 5 to 12 μmol ATP g −1 biomass C but trends between biomass ATP and incubation temperatures were not very obvious until about day 13. On day 23, biomass ATP concentrations were positively and linearly related to temperature: (μmol ATP g −1 biomass C = 6.98 ± 0.35 + 0.134 ± 0.023 T 0 ( r 2 = 0.77) with no significant difference in the slope between the grassland and arable soils. At 25°C the biomass ATP concentration was 10.3 μmol g −1 biomass C, remarkably close to many other published values. It was concluded that, although the biomass increased its ATP concentration in response to increasing temperature, the increase was comparatively small. Also, at all temperatures tested, the biomass maintained its ATP concentration within the range commonly reported for micro-organisms growing expontentially in vitro. This is despite the fact that the biomass normally exhibits other features more typical of a “resting” or dormant population — a paradox which still is not resolved.

Changes in soil microbial properties as indicators of adverse effects of heavy metals

Abstract: In high-productivity agricultural ecosystems, natural soil fertility is commonly supplemented by applications of nutrients, either as inorganic fertilizer or organic manures, and occasionally both. However, the activities of the soil micro-organisms (collectively the soil microbial biomass) in decomposing plant and animal residues and in the formation and mineralization of soil organic matter still underpins the fertility of these managed systems. In natural ecosystems these natural processes determine, almost entirely, the fertility of their soils. Any decline in natural soil fertility will therefore have disproportionately large effects in natural systems but still cannot be ignored in managed ones. The soil-plant ecosystem may be damaged, either in the longor short-term, by agents that inhibit or stop the natural functioning of the soil micro-organisms. The heavy metals, e.g. Cu, Ni, Cd, Cr, Zn, Pb, are by far the most important inorganic pollutants of soil. They differ from organic pollutants in that, once they have entered soil they persist, for all practical purposes, indefinitely. Currently, the only practical means of their removal is to remove the soil itself, hardly a practical proposition in most cases. Mandatory European Union (EU) limits are designed to stop the accumulation of heavy metals above ‘safe’ soil metal concentrations. The limits are based upon known effects of heavy metals on plant and animal health. Until recently, they took no account of possible effects on soil micro-organisms or microbial actvities despite their essential role in maintaining soil fertility.