Martti Esala

National and regional net nitrogen balances in Finland in 1990-2005

Nitrogen (N) balance has been identified as a principal agri-environmental indicator. In addition to national N balances, calculation of N balances for different agricultural regions is also recommended. In this study, national and regional net N balances for Finland were calculated. The net N balance is the result of deducting the NH3-N losses from manure and fertilisers from the gross N balance. The N balance calculation was based on data for Finnish Rural Centres and calculated per cultivated hectare. The main data inputs for the calculations were agricultural and environmental statistics, coefficients of manure excretion and crop N concentrations. Finnish national net N balance decreased from 90 kg ha –1 in 1990 to 50 kg ha –1 in 2005. The decrease in regional N balances was of the same magnitude. The main reason for the lower N balances was reduced use of mineral N fertilisers. Variation in the N balances was due to yield levels varying according to growing season conditions. The Rural Centres with intensive animal production tended to generate the highest N balances.

Tillage and crop residue management methods had minor effects on the stock and stabilization of topsoil carbon in a 30-year field experiment

We studied the effects of tillage and straw management on soil aggregation and soil carbon sequestration in a 30-year split-plot experiment on clay soil in southern Finland. The experimental plots were under conventional or reduced tillage with straw retained, removed or burnt. Wet sieving was done to study organic carbon and soil composition divided in four fractions: 1) large macroaggregates, 2) small macroaggregates, 3) microaggregates and 4) silt and clay. To further estimate the stability of carbon in the soil, coarse particulate organic matter, microaggregates and silt and clay were isolated from the macroaggregates. Total carbon stock in the topsoil (equivalent to 200 kg m(-2)) was slightly lower under reduced tillage (5.0 kg m(-2)) than under conventional tillage (5.2 kg m(-2)). Reduced tillage changed the soil composition by increasing the percentage of macroaggregates and decreasing the percentage of microaggregates. There was no evidence of differences in the composition of the macroaggregates or carbon content in the macroaggregate-occluded fractions. However, due to the higher total amount of macroaggregates in the soil, more carbon was bound to the macroaggregate-occluded microaggregates in reduced tillage. Compared with plowed soil, the density of deep burrowing earthworms (Lumbricus terrestris) was considerably higher under reduced tillage and positively associated with the percentage of large macroaggregates. The total amount of microbial biomass carbon did not differ between the treatments. Straw management did not have discernible effects either on soil aggregation or soil carbon stock. We conclude that although reduced tillage can improve clay soil structure, generally the chances to increase topsoil carbon sequestration by reduced tillage or straw management practices appear limited in cereal monoculture systems of the boreal region. This may be related to the already high C content of soils, the precipitation level favoring decomposition and aggregate turnover in the winter with topsoil frost.

Plant recovery of 15N-labelled nitrogen applied to reed canary grass grown for biomass

Reed canary grass (Phalaris arundinacea L.) is apotential crop for production of bioenergy and biomass in northern Europe. In this study labelled 15N was used to follow the fate of applied N in roots and shoots of reed canary grass during a year. Two rates of15N fertiliser were applied in spring 1995 and 1996 to a clay (50 kg ha−1 and 100 kg ha−1) and an organic soil (30 kg ha−1 and 60 kg ha−1). The data did not indicate significant differences between recoveries of nitrogen following application of fertiliser at recommended and half of the recommended rates. The recovery of added N in shoots was highest at midsummer. The median values were 68% and 58% inorganic soil and 42% and 65% in clay soil, in 1995 and 1996respectively. Some of the N utilised by shoots was remobilised to the roots during autumn. The highest median recovery of applied N in roots was 19%in clay soil in October 1996, corresponding to a 13 percentage unit increase in recovery during autumn. In contrast, the lowest remobilisation was recorded after a rainy spring in clay soil, being only 3 percentage units. During winter the loss of N and fertiliser N from the shoots continued, and consequently the total N content in shoots was about half of that for autumn. In spring, one year after N application, the shoots contained 9–20% of applied N. The data suggest both intensive uptake and remobilisation of fertiliser N during over a year, following delayed harvest, and indicate the importance of the rhizome system in N turnover.