Background and aims Organic inputs have a positive effect on the soil organic matter balance. They are therefore an important asset for soil fertility and crop growth. This study quantifies the additional yield effect due to organic inputs for arable crops in Europe when macronutrients are not a limiting factor. Methods A meta-analysis was performed using data from 20 long-term experiments in Europe. Maxima of yield response curves to nitrogen were compared, with and without organic inputs, under abundant P and K supply. Results We were surprised to find that, across all experiments, the mean additional yield effect of organic inputs was not significant (+ 1.4 % ± 1.6 (95 % confidence interval)). In specific cases however, especially for root and tuber crops, spring sown cereals, or for very sandy soils or wet climates, organic inputs did increase attainable yields. A significant correlation was found between increase in attainable yields and increase in soil organic matter content. Conclusions Aggregating data from 20 long-term experiments in Europe, this study shows that organic inputs and/ or soil organic matter do not necessarily increase yields, given sufficient nutrients are supplied by mineral fertilisers. Results show the relevance of some environmental factors for additional yield effect of organic inputs, but no simple relation between organic inputs and crop growth.

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Abstract. Implementation of the Nitrates Directive (NiD) and its environmental impacts were compared for member states in the northwest of the European Union (Ireland, United Kingdom, Denmark, the Netherlands, Belgium, Northern France and Germany). The main sources of data were national reports for the third reporting period for the NiD (2004NiD ( -2007 and results of the MITERRA-EUROPE model. Implementation of the NiD in the considered member states is fairly comparable regarding restrictions for where and when to apply fertilizer and manure, but very different regarding application limits for N fertilization. Issues of concern and improvement of the implementation of the NiD are accounting for the fertilizer value of nitrogen in manure, and relating application limits for total nitrogen (N) to potential crop yield and N removal. The most significant environmental effect of the implementation of the NiD since 1995 is a major contribution to the decrease of the soil N balance (N surplus), particularly in Belgium, Denmark, Ireland, the Netherlands and the United Kingdom. This decrease is accompanied by a modest decrease of nitrate concentrations since 2000 in fresh surface waters in most countries. This decrease is less prominent for groundwater in view of delayed response of nitrate in deep aquifers. In spite of improved fertilization practices, the southeast of the Netherlands, the Flemish Region and Brittany remain to be regions of major concern in view of a combination of a high nitrogen surplus, high leaching fractions to groundwater and tenacious exceedance of the water quality standards. On average the gross N balance in 2008 for the seven member states in EU-ROSTAT and in national reports was about 20 kg N ha −1 yr −1 lower than by MITERRA. The major cause is higher estimates of N removal in national reports which can amount to more than 50 kg N ha −1 yr −1 . Differences between procedures in member states to assess nitrogen balances and waterPublished by Copernicus Publications on behalf of the European Geosciences Union. H. J. M. van Grinsven et al.: Benchmarking the Nitrates Directive in northwestern Europequality and a lack of cross-boundary policy evaluations are handicaps when benchmarking the effectiveness of the NiD. This provides a challenge for the European Commission and its member states, as the NiD remains an important piece of legislation for protecting drinking water quality in regions with many private or small public production facilities and controlling aquatic eutrophication from agricultural sources.

The concept of a constant seepage and percolation ( SP) rate in monitoring the water balance of flooded rice fields, as often used in e.g. irrigation system design and management, was investigated. First, magnitude and variability of percolation rate were studied for different combinations of soilhydraulic properties and hydrologic conditions using the validated water balance model SAW AH.Percolation losses from fields with relatively low subsoil permeability ( ks,sub < 10- Only in the latter case, percolation rates are largely affected by the depth of ponded water. Next, the constancy of combined SP rates was studied in a field experiment on a permeable subsoil. Simple book-keeping of the water balance using a fixed SP rate proved accurate to predict the depth of ponded water in time in case of a poorly permeable plow sole and a small seepage component. A decision tree was suggested based on soil-hydraulic properties and characteristics ofbunds to estimate the magnitude and variation of SP rates, and to decide whether book-keeping with a fixed SP rate is an appropriate tool in monitoring the water balance of paddy fields.

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The water use efficiency of a flooded puddled rice field was studied through analysis of the components of the water balance in the field and through simulation modelling. Seepage and percolation ( SP) losses were the main determinants of water use efficiency in a field experiment conducted in the Philippines. Seepage through and underneath bunds can greatly increase total water loss. Seepage and percolation rates in well-puddled soil varied from 0.4 em· d -I without seepage to 3.62 em· d-1 with seepage, and cumulative SP losses varied between 90 and 350 em per crop cycle, respectively. The vertical profile of an irrigated puddled rice soil can schematically be described by a layer of ponded water, a muddy layer with little resistance to water flow, a plow sole with large resistance to water flow, and the non-puddled subsoil. Using this concept, the one-dimensional flow model SAW AH (Simulation Algorithm for Water flow in Aquic Habitats) accurately simulated ponded water depth and pressure head gradients within the soil profile for the test field without seepage, using measured soil-hydraulic input data.

Mineral carbonation of basic silicate minerals regulates atmospheric CO2 on geological time scales by locking up carbon. Mining and spreading onto the earth's surface of fast-weathering silicates, such as olivine, has been proposed to speed up this natural CO2 sequestration (‘enhanced weathering’). While agriculture may offer an existing infrastructure, weathering rate and impacts on soil and plant are largely unknown. Our objectives were to assess weathering of olivine in soil, and its effects on plant growth and nutrient uptake. In a pot experiment with perennial ryegrass (Lolium perenne L.), weathering during 32 weeks was inferred from bioavailability of magnesium (Mg) in soil and plant. Olivine doses were equivalent to 1630 (OLIV1), 8150, 40700 and 204000 (OLIV4) kg ha−1. Alternatively, the soluble Mg salt kieserite was applied for reference. Olivine increased plant growth (+15.6%) and plant K concentration (+16.5%) in OLIV4. At all doses, olivine increased bioavailability of Mg and Ni in soil, as well as uptake of Mg, Si and Ni in plants. Olivine suppressed Ca uptake. Weathering estimated from a Mg balance was equivalent to 240 kg ha−1 (14.8% of dose, OLIV1) to 2240 kg ha−1 (1.1%, OLIV4). This corresponds to gross CO2 sequestration of 290 to 2690 kg ha−1 (29 103 to 269 103 kg km−2.) Alternatively, weathering estimated from similarity with kieserite treatments ranged from 13% to 58% for OLIV1. The Olsen model for olivine carbonation predicted 4.0% to 9.0% weathering for our case, independent of olivine dose. Our % values observed at high doses were smaller than this, suggesting negative feedbacks in soil. Yet, weathering appears fast enough to support the ‘enhanced weathering’ concept. In agriculture, olivine doses must remain within limits to avoid imbalances in plant nutrition, notably at low Ca availability; and to avoid Ni accumulation in soil and crop.