Showing papers by "Philip C. Brookes published in 1998"

Temperature effects on organic matter and microbial biomass dynamics in temperate and tropical soils

Abstract: The aim was to investigate whether soils developed under tropical conditions had different organic matter and microbial biomass dynamics than soils developed under temperate ones. Three soils formed under temperate climatic conditions (U.K.) and three under tropical conditions (Brazilian) were selected to be as comparable as possible in terms of organic matter, clay content and pH. They were then incubated moist at 15°C or 35°C for 150 d. Carbon dioxide evolution and microbial biomass were measured at intervals during the incubation. The biomasses in the tropical soils declined more slowly at both temperatures than in the temperate soils, although at 15°C the differences were mainly small. At 35°C the decline was generally much more marked in the temperate soils (60–75% of the initial value) than in the tropical ones (15, 40 and 60%). Soil organic matter was mineralised more rapidly in the temperate than the tropical soils: at 35°C up to 9–10 times more CO 2 –C was evolved than was contained in the temperate biomasses during the 150 d incubation. The comparable maximum value for the tropical soils was 4.5 times. These results seem to indicate that the organic matter in the tropical soils was more degraded, or humified, than that in the temperate soils. An attempt to quantify the extent of humification was made using differential thermal analysis (DTA) and thermogravimetric analysis (TG). Both methods also indicated that the organic matter was generally more humified in the tropical than temperate soils. It was concluded that DTA and TG may both be useful techniques in studying soil organic matter dynamics, especially when linked to studies of soil microbial dynamics.

Microbial biomass and soil organic matter dynamics in oil palm (Elaeis guineensis Jacq.) plantations, West Malaysia

Abstract: We used the chloroform fumigation-extraction method to investigate relationships between microbial biomass C and total organic C, and between microbial biomass ninhydrin-N and total organic N, in areas within oil palm plantations receiving different amounts of organic matter over 5, 10 and 20 y. The avenues and weeded circles beneath the palms, which comprised 65% and 15% and of the area respectively, had mean organic concentrations of 0.82% at 5 y, 1.76% at 10 y and 2.21% at 20 y. These areas received negligible inputs of litter from above-ground during the life of the plantation and the increments in soil organic matter must have been largely derived from root material. In contrast, windrows of pruned fronds, occupying 20% of the area, received annual inputs of up to 10 t ha−1 of organic matter (equivalent to 4.8 t C ha−1 y−1) but the carbon content of the underlying soils only increased from 0.82% at 5 y, to 2.47% at 10 y and 3.09% at 20 y. Values for biomass C varied from 109 to 390 μg C g−1 with highest values under the palm fronds. Biomass ninhydrin-N (Nnin), varying between 2.2 and 14.3 μg N g−1, was significantly correlated with biomass C (Cmic), soil organic C (Corg) and organic N, and was shown to be a reliable alternative to biomass C determinations for estimating microbial biomass in these soils. The C-to-N ratio of microbial biomass (Cmic:Nnin) varied between 26 and 50 with a mean of 31; no trends were evident in relation to age of site or location within sites. At 5 y % Cmic in Corg was larger (2.40%) under the frond piles than in the avenues (1.70%) and the weeded circles (1.36%). In the 10 and 20 y-old plantations, however, % Cmic in Corg declined under the frond piles relative to other treatments. It was concluded that microbial biomass C generally increased as a function of increasing total organic C related to the age of the plantation but was not consistently higher under frond piles which received much higher inputs of organic matter than the avenues and circles. This suggested that most of the frond material decomposed on the soil surface and did not significantly affect soil microbial biomass.

Chlordane transport in a sandy soil: effects of suspended soil material and pig slurry

Abstract: Summary In experiments in lysimeters of sandy soil chlordane was transported in water flows only when sorbed on suspended soil material. A chlordane ‘concentration’ was calculated by dividing this sorbed chlordane by the volume of the water sample in which the suspended matter was carried. In all but one lysimeter the first peak in this ‘concentration’ appeared in the drainage well ahead of the first peak in the concentration of bromide applied at the same time as the chlordane. Chlordane also persisted in the drainage for less time than bromide. The transport of chlordane was most closely associated with that of the largest category of suspended soil material (> 1.2 μm), possibly because that category contained the most organic matter. It was not associated with the transport of colloidal matter for either of the two possible size limits applied to the latter (< 0.22 μm or < 0.45 μm). In the lysimeters to which pig slurry was applied the evidence that it enhanced the transport of chlordane was limited and equivocal; the chlordane was probably sorbed strongly by the soil's organic matter before the slurry was applied. The application of chlordane was 100 times greater than in normal agricultural practice and it was followed by a substantial volume of water. Nevertheless, only 0.00002% of it was transported from the lysimeters, and its ‘concentration’, calculated as above, never exceeded the EU limit of 0.1 μg1−1 for any one pesticide.

Phosphorus movement in drainage water from the Broadbalk Experiment

Abstract: Phosphorus (P) may be lost from agricultural land to water by several processes. These include erosion, surface runoff and subsurface flow (leaching). As most soils have a very high absorption capacity for P, usually far exceeding the quantities of P added as manures or fertilizers, it has long been considered that leaching losses of P from soil to water are negligible in most cases. While this is certainly true in terms of economic losses to the farmer, the concentrations of P required to trigger eutrophication in freshwater are extremely small (as low as 0.02 to 0.035 mg P l). Indeed, the quality of surface waters throughout Europe, in terms of risk of eutrophication, is a major current concern because of the increasing concentrations of P. In much work it is difficult to precisely relate P loss to soil P concentrations, either in the plough layer or subsoil, simply because such data are either not given or are insufficient. Here, we report the results of systematic studies of the relationships between soil P status and P losses to drainage water, in silty loam soils of the Broadbalk Continuous Wheat Experiment, UK given mainly inorganic fertilizer. We also assess some of the possible mechanisms involved.