Maija Paasonen-Kivekäs

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

Application of a two-dimensional model to calculate water balance of an agricultural hillslope

Abstract The objective was to simulate runoff production on an agricultural hillslope in Southern Finland. Water balance was calculated using a quasi-two-dimensional model describing vertical soil moisture distribution and horizontal water movement along a hillslope strip. The model accounted for the production of saturated overland flow on the exfiltration part of the hillslope. The model results were assessed against measurements of surface runoff, subsurface drainage flow, and water table level, which were available at individual field sections for years 1995-96. Intensive runoff events during summer and autumn rainfalls were the primary focus in the modeling application. The model performed well during wet periods when water table remained close to the soil surface, but the results were less satisfactory during dry periods.

Simulating water balance and evapotranspiration in a subsurface drained clayey agricultural field in high-latitude conditions

Secondary drainage impact of groundwater outflow can affect drainage design and form a pathway for nutrient loading in agricultural areas. Holistic assessment of water balance and all outflow pathways can benefit design of sustainable drainage in a changing climate. In this study, three-dimensional, hydrological FLUSH model was applied to investigate a field-scale data set and to produce a closure of water balance throughout all seasons in a clayey subsurface drained agricultural field in high-latitude conditions. Description of evapotranspiration (ET)-groundwater interactions using a three-dimensional hydrological model provides a new approach for evaluating standard computational methods to estimate ET with limited crop data. Different ET estimates were tested in the context of total water balance, and the coupling of ET and groundwater outflow was assessed. Comparison of measured and simulated water balance components demonstrated that reference ET (Penman–Monteith method) overestimated ET in the cropped field in high latitude conditions. The FAO-56 single crop coefficient approach was also noted to overestimate ET in the studied conditions. A calibrated constant crop coefficient satisfactorily described ET in spring and in autumn, but underestimated it during summer periods. The results suggest that care should be taken when applying standard methods in high-latitude conditions. Groundwater outflow and ET were shown to be interlinked, but even a relatively high potential ET affected the amount of groundwater outflow only slightly. The results demonstrate that groundwater outflow can form an important component of the water balance in clayey subsurface drained fields. The strength of the 3D model was demonstrated in showing how ET had an impact on all outflow components of drained field sections. Such a modelling tool is useful for generating scenarios that show how changes in climate forcing and thereby ET can alter the partitioning of the field-scale water balance.

Development and application of a solute transport model to describe field-scale nitrogen processes during autumn rains

A new generic, three-dimensional, solute transport component was developed into FLUSH, which is a hydrological model developed for Nordic conditions. Water flow and solute transport descriptions in FLUSH follow the dual-permeability concept, which divides the total soil pore space into mobile soil matrix and macropore systems. The solute transport model was parameterized to simulate the main processes of nitrogen (N) cycle in clayey, subsurface-drained soils during autumn periods after the harvest. The model simulates transport of nitrate and ammonium N, as well as mineralization, nitrification, and denitrification. Reactions in soil are affected by temperature and moisture, as simulated by FLUSH. Ammonium can adsorb on soil particles in both pore systems, while organic N is described in simulations as an immobile solute in the soil matrix. One-dimensional version of the model was applied to two subdrained field sections (1.3 and 3.4 ha) in the Nummela experimental field in southern Finland during two autumn periods (2008 and 2011). The model was able to replicate the measured dynamics of nitrate N concentrations in drain discharge during both the periods. Concentrations were the most dependent on drain discharge dynamics and the rate of nitrification. Measured and simulated ammonium concentrations in drain discharge were about 10 times smaller than nitrate concentrations, even though the levels of N input with initial values and deposition for both inorganic fractions were similar. Successful solute transport simulation results further increase the confidence in the description of the water flow processes in FLUSH.

Nutrient Load from Two Drainage Systems on Clay Soil

In the southern and the south-western parts of Finland 75% of the arable land has subsurface drainage. The Finnish state subsidizes subsurface drainage on certain conditions including for example different envelope materials, drain depth and total drain length per hectare. The typical drain depth is 1.0-1.2 m and the drain spacing varies mostly between 12 and 26 meters depending on the soil type. Gravel is the most common envelope, but also synthetic and semisynthetic textile, cocos fibre and wood chips are used. The aim of this study is to find out how two different kind of drainage methods affect crop production and nutrient load in both drainage waters and surface runoff. In the method I gravel is used as an envelope and the drain spacing is 8 m. In the method II very thin textile (<1 mm) is used as an envelope and drain spacing is 6 m. The research is carried out on a field at Jokioinen in south-western Finland. The soil is heavy clay and the mean slope is 1%. The existing tile drainage pipes were laid in 1954 using 16 m spacing and an average depth of 1 m. The size of the field is 6 ha and it consists of 3 field sections each with a separate drainage system. In the summer of 2008, the additional drainage systems were built into two of the field sections using the methods I and II . The third one was left as a control plot. Runoff volume and water quality of subsurface and surface waters and crop yield from each field section have been measured. Concentrations of total phosphorus, dissolved orthophosphate, total nitrogen, ammonium nitrate, nitrate nitrogen and solid substances have been determined from the samples. In the paper runoff, nutrient load and crop yield from the calibration and testing periods are presented. The feasibility of the two drainage methods is evaluated from the point of view of crop production and nutrient loading to surface waters.