Markku Yli-Halla

Assessment of soluble phosphorus load in surface runoff by soil analyses

Abstract A series of laboratory experiments was carried out to quantify physical and chemical factors that control the level of soluble P in soil suspensions. The objective was to identify the variables needed in models simulating the load of dissolved reactive P (DRP) in the surface runoff from cultivated land. Release of soil P as a function of water-to-soil ratio and ionic strength was investigated with soil samples collected from two experimental fields. The dynamic relationship between soil and solution P was studied by sorption-desorption isotherms. The results of the laboratory tests were compared with the mean flow-weighted concentration of DRP in the runoff water from the fields. The DRP concentration was too high to have originated solely from the eroded soil material transported in the runoff. It was concluded that DRP arose mainly by the desorption of P from the surface soil during a rain or snow-melt period. The mean DRP concentration seems to be primarily controlled by the P status of the surface soil. The DRP concentration of soil extracts obtained at wate-to-soil ratios of 250–1001 kg −1 (soil concentration range of 4–10 g l −1 ) corresponded to the flow-weighted mean DRP concentrations of surface runoff water and may thus be used to quantify the removal of DRP by surface runoff. The variations in the ionic strength and water-to-soil ratio in the surface soil may control the temporal variation of the DRP in the runoff water. In the present soils, a series of water extractions at different water-to-soil ratios was found to be a more reliable procedure in assessing the potential P load than the parameters derived from sorption-desorption isotherms.

Oxidation-induced leaching of sulphate and cations from acid sulphate soils

Leaching of sulphate and cations from horizon samples of two acid sulphate soils (0.9 to 1.6% S in subsoil) was studied in the laboratory. Samples were incubated and eluted with water at 20 °C and 5 °C until apparent exhaustion of leachable S resources. The leachates were analyzed for pH, SO4-S, Fe, Al, Mn, K, Ca, Mg, and Na.Oxidation of sulphide was retarded at the lower temperature. From all the originally water-logged samples the sulphate formed was initially washed out with base cations (mainly with Mg), but the proportion of acid counter ions (predominantly Al) increased with proceeding oxidation and acid formation. In the most acid leachates, pH was 2.6 to 2.8. In the transition layer between reduced and oxidized horizons, sulphide oxidation had been going on for some time, and acid cations were the main counter ions for sulphate already at the beginning of the experiment. In the totally oxidized surface horizons, sulphate was leached only in moderate quantities, and the sum of cation equivalents (mainly base species) exceeded that of sulphate, suggesting some removal of other anions.Leaching losses in the laboratory experiment, corresponding to drainage-induced loading of waters in field experiments during the course of many decades, point out the environmental danger associated with deep drainage of potentially acid sulphate soils.

Land Improvements under Land Tenure Insecurity: The Case of pH and Phosphate in Finland

This study analyses whether the land tenure insecurity problem decreases long-term land improvements (liming and phosphorus fertilization) under the Common Agricultural Policy (CAP) and Nordic production conditions in the European Union (EU) countries, such as Finland. Our study suggests that under the traditional cash lease contracts, which are encouraged by the existing land leasing regulations and agricultural subsidy programs, the land tenure insecurity problem on leased land decreases land improvements that have a long pay-back period. In particular, soil pH was found to be significantly lower in the land cultivated under a lease contract compared to land owned by the farmers themselves. (JEL Q15, Q24, Q28)

Response of pore water Al, Fe and S concentrations to waterlogging in a boreal acid sulphate soil.

Environmental hazards caused by acid sulphate (AS) soils are of worldwide concern. Among various mitigation measures, waterlogging has mainly been studied in subtropical and tropical conditions. To assess the environmental relevance of waterlogging as a mitigation option in boreal AS soils, we arranged a 2.5-year experiment with monolithic lysimeters to monitor changes in the soil redox potential, pH and the concentrations of aluminium (Al), iron (Fe) and sulphur (S) in pore water in response to low and high groundwater levels in four AS soil horizons. The monoliths consisted of acidic oxidized B horizons and a reduced C horizon containing sulphidic material. Eight lysimeters were cropped (reed canary grass, Phalaris arundinacea) and two were bare without a crop. Waterlogging was conducive to reduction reactions causing a slight rise in pH, a substantial increase in Fe (Fepw) and a decrease in Al (Alpw) in the pore water. The increase in Fepw was decisively higher in the cropped waterlogged lysimeters than in the bare ones, which was attributable to the microbiologically catalysed reductive dissolution of poorly ordered iron oxides and secondary minerals. In contrast to warmer climates, Fepw concentrations remained high throughout the experiment, indicating that the reduction was poised in the iron range, while sulphate was not reduced to sulphide. Therefore, the precipitation of iron sulphide was negligible in the environment with a low pH and abundant with poorly ordered Fe oxides. Increased Fe in pore water counteracts the positive effects of waterlogging, when water is flushed from fields to watercourses, where re-oxidation of Fe causes acidity and oxygen depletion. However, waterlogging prevented further oxidation of sulphidic materials and decreased Alpw to one-tenth of the initial concentrations, and even to one-hundredth of the levels in the low water table lysimeters.

A comparison of nitrogen and carbon reserves in acid sulphate and non acid sulphate soils in western Finland

Previous studies suggest that nitrogen (N) loads from acid sulphate soil (AS soil) catchments in Finland are higher than those from other agricultural catchments. This study seeks to explain this difference by measuring carbon (C) and N profiles in both an AS soil and a neighbouring non AS soil. In Lapua, western Finland, two adjacent fields (Dystric Cambisols), subjected to similar agricultural practices, were analysed to the depth of 240 cm for pH, total C (Ctot), total N (Ntot), NH4 + -N, NO3 -N, sulphur and bulk density. Field A, an AS soil, contained sulfidic materials and 0.9% Ctot below 170 cm, while Field B, not an AS soil, had 0.3% Ctot in the subsoil and no sulfides. In these soils, the groundwater level declined below 200 cm in summer, subjecting the subsoil to oxidation. This study revealed large stocks of Ctot, Ntot, and mineral N in the subsoil, particularly in the AS soil. At 20–240 cm, Field A contained 292 tons of Ctot ha -1 and 25 tons of Ntot ha -1 , while Field B had 152 tons of Ctot ha -1 and 11 tons of Ntot ha -1

The microbial communities and potential greenhouse gas production in boreal acid sulphate, non-acid sulphate, and reedy sulphidic soils.

Acid sulphate (AS) soils along the Baltic coasts contain significant amounts of organic carbon and nitrogen in their subsoils. The abundance, composition, and activity of microbial communities throughout the AS soil profile were analysed. The data from a drained AS soil were compared with those from a drained non-AS soil and a pristine wetland soil from the same region. Moreover, the potential production of methane, carbon dioxide, and nitrous oxide from the soils was determined under laboratory conditions. Direct microscopic counting, glucose-induced respiration (GIR), whole cell hybridisation, and extended phospholipid fatty acid (PLFA) analysis confirmed the presence of abundant microbial communities in the topsoil and also in the deepest Cg2 horizon of the AS soil. The patterns of microbial counts, biomass and activity in the profile of the AS soil and partly also in the non-AS soil therefore differed from the general tendency of gradual decreases in soil profiles. High respiration in the deepest Cg2 horizon of the AS soil (5.66 μg Cg(-1)h(-1), as compared to 2.71 μg Cg(-1)h(-1) in a top Ap horizon) is unusual but reasonable given the large amount of organic carbon in this horizon. Nitrous oxide production peaked in the BCgc horizon of the AS and in the BC horizon of the non-AS soil, but the peak value was ten-fold higher in the AS soil than in the non-AS soil (82.3 vs. 8.6 ng Ng(-1)d(-1)). The data suggest that boreal AS soils on the Baltic coast contain high microbial abundance and activity. This, together with the abundant carbon and total and mineral nitrogen in the deep layers of AS soils, may result in substantial gas production. Consequently, high GHG emissions could occur, for example, when the generally high water table is lowered because of arable farming.

Pre-crop effects on the nutrient composition and utilization efficiency of faba bean ( Vicia faba L.) and narrow-leafed lupin ( Lupinus angustifolius L.)

Legumes are key components of cropping systems due to their biological nitrogen fixation ability. The beneficial role of legumes as pre-crops for cereals in cereal-based rotations is well studied, but the evaluation of pre-crops for legumes is not. This study aims to identify which is the best pre-crop for faba bean and narrow-leafed lupin by comparing various nutrient utilization indices for 11 elements. The elemental composition of the two grain legumes was significantly different. There was a significant and positive pre-crop effect of barley, and to a lesser extent oat, on the nutrient composition and indices of both grain legumes, but not on their yield and protein concentration. Barley as a pre-crop was associated with higher concentrations of Mg, Mn and Zn in narrow-leafed lupin seeds and of S in faba bean seeds. Principal component analysis demonstrated similarities in the nutrient uptake of both legumes, and also revealed a consistent association between Fe and Si in narrow-leafed lupin. Use of different nutrient utilization indices allows the detection of pre-crop effects in rotations and the assessment of nutrient cycling of different crop sequences. The mineral utilization index was particularly informative. Attention to the appropriate pre-crop can further increase the sustainability of legume-supported cropping systems.

Groundwater management of acid sulfate soils using controlled drainage, by-pass flow prevention, and subsurface irrigation on a boreal farmland

Sulfide-bearing anoxic sediments are found in coastal regions around the world including Australia and the Baltic. Upon lowering of the groundwater by drainage, they are oxidized and form acid sulfate soils (pH < 4) that mobilize plenty of potentially toxic metals into watercourses with serious environmental consequences. Being highly valued for their excellent crop yields, there is an urgent need to find management solutions that minimize the oxidation. In this study, possibilities to manage the groundwater with controlled subsurface drainage (CD) and subsurface irrigation (CDI), which included a vertical plastic sheet to prevent by-pass flow into the main drain, was examined on a Boreal farmland in Western Finland. During a 3-year study, the groundwater in the reference field (Ref) with conventional subsurface drainage pipes at 1.1–1.4 m depth typically dropped down to almost 2 m in the end of summers (September) due to evapotranspiration exceeding precipitation. CD delayed the groundwater drop, shortening the time of oxidation. In CDI system, the groundwater could be kept at c. 1 m or shallower throughout the summers, thereby preventing oxidation of critical sulfide horizons in the lower subsoil. Differences in total discharge and soil geochemistry features were small during the course of the study period. Salt accumulation seemed to be a small risk for crop growth but the capillary rise of acidity to the surface horizon may be increased in CDI, possibly increasing the need for surface liming. A “floating groundwater antenna,” indicating groundwater fluctuations, proved to be an easy and reliable tool to farmers for proper management of controlled drainage.

Measured and simulated effects of sophisticated drainage techniques on groundwater level and runoff hydrochemistry in areas of boreal acid sulphate soils

To abate the environmental problems caused by the severe acidity and high metal concentrations in rivers draining acid sulphate (AS) soils of Western Finland, control drainage (CD) and lime filter drainage (LFD), and their combination, were investigated. The effectiveness of these best management practices (BMP’s) on drainage water quality was studied on plot scale in two locations. In Ilmajoki, where the sulphidic materials are more than 2 m below the soil surface, CD efficiently reduced the concentrations of sulphate, aluminium, manganese and iron concentrations and to some extent also increased the pH of the drainage waters. LFD, in contrast, effectively reduced the drainage water acidity and raised the pH level. Decrease of the groundwater level owing to strong evapotranspiration in summer could, however, not be properly prevented by CD. In Mustasaari where sulphidic materials were as shallow as 1 m below soil surface, the positive effects of LFD recognised in Ilmajoki were hardly seen. This shows, that the tested BMP’s work properly, and can thus be recommended, for intensively artificially drained AS soils like in Ilmajoki where most of the acidity has already been transported to watercourses. LFD can, however, not be recommended for as yet poorly leached and thus particularly problematic AS soils like in Mustasaari. This is, of course, a drawback of the tested BMP, as it is not effective for the soils which would need it most. The field data were tentatively utilised to test the performance of the HAPSU (Ionic Flow Model for Acid Sulphate Soils) simulation model developed to estimate the loads of harmful substances from AS soils.

Phosphorus status, inorganic phosphorus forms, and other physicochemical properties of acid soils of Farta District, Northwestern Highlands of Ethiopia

Soil acidity and low availability of P limit crop production in the highlands of Ethiopia. The objective of this study was to determine the P status, distribution and forms of inorganic P and relate them to selected chemical properties of eight representative acidic surface soil samples from Farta District. Soil pH (H2O) varied between 4.74 and 5.50. The moderate to high CEC suggests that besides kaolinite, the soils also contain expandable 2 : 1 clay minerals. Though the total P content was high, the available Olsen P content was very low or low in all soils except one. In most soils, the abundance of inorganic P fractions was as follows: P bound by oxalate extractable iron (-P) reductant soluble Fe-P occluded Al-Fe-P P bound by oxalate extractable aluminum (-P) calcium bound P (Ca-P). Olsen P had a very strong positive correlation () with -P (), -P (), and oxalate extractable P (). Though Fe bound P reserves were quite abundant and the degree of P saturation of