Sofia Delin

Relations Between Net Nitrogen Mineralization and Soil Characteristics Within an Arable Field

Within-field variations in plant-available soil nitrogen (N) are likely to be affected by differences in soil characteristics. To study this, a 3- year field investigation was conducted during 1998-2000 on a 15 ha arable field in Sweden with considerable within-field soil texture variability. In 34 plots soil N uptake by crops, net nitrogen mineralization (Nm) during the growing season and soil mineral N in spring and shortly after harvest were determined. Beside these parameters, topography, soil organic matter content (SOM), clay content, pH(H 2 O) and grain yield were recorded. The variations in Nm were considerably large both within the field and between years. The within-field variation in Nm could partly be explained by the variation in SOM and clay content (adjusted coefficient of determination = 0.23, P <0.001). The pattern in Nm differed between years, partly because of seasonal variations in soil moisture. For these reasons, the pattern of Nm is difficult to predict without seasonal adjustments.

Management Zones Classified With Respect to Drought and Waterlogging

Within-field variations in potential grain yield may be due to variations in plant available soil water. Different water holding capacities affect yield differently in different years depending on weather. By estimating plant-water availability in different weathers, scenarios could be created of how yield potential and thereby fertilizer demand may vary within fields. To test this, measured cereal grain yields from a dry, a wet and an intermediate year were compared with different soil moisture related variables in a Swedish arable field consisting of clayey and sandy areas. Soil water budget calculations based on weather data and maximum plant available water (PAW), estimated from soil type and rooting data, were used to assess drought. A reasonable correlation between estimated and measured soil moisture was achieved. In the dry year, drought days explained differences in yield between the clayey and the sandy soil, but yield was better explained directly by maximum PAW, elevation, clay content and soil electrical conductivity (SEC). Yield correlated significantly with SEC and elevation within the sandy soil in the dry year and within the clayey soil in the wet year, probably due to water and nitrogen limitation respectively. Dense SEC, elevation and yield data were therefore used to divide the field into management zones representing different risk levels for drought and waterlogging. These could be used as a decision support tool for site-specific N fertilization, since both drought and waterlogging affect N fertilization demand.

Timing of organic fertiliser application to synchronise nitrogen supply with crop demand

Abstract To achieve high nitrogen (N)-use efficiency, N availability from organic fertilisers must be synchronised with crop uptake. In order to estimate when previously unmineralised N is plant-available in relation to fertilisation time-point, net N mineralisation was studied in incubations under natural temperature conditions. The fertilisers studied were meat and bone meal (Biofer), dairy slurry, dairy manure, chicken manure, and a by-product from yeast production (Vinasse). The fertilisers were mixed with soil and incubated in plastic bottles placed in topsoil in south-west Sweden on different dates throughout the year, simulating fertiliser application in autumn, early spring, spring, and early summer. Bottles were sampled for analysis of NH4-N and NO3-N on three to seven occasions until late autumn and the experiment was repeated in two consecutive years. Dairy slurry and dairy manure had a very slow, almost negligible, net N mineralisation after application. Slurry with rather high ammonium content should therefore be applied as close to crop demand as other circumstances allow, whereas dairy farmyard manure with very low mineral N content can be applied off-season. Chicken manure had a considerable proportion of mineral N initially, but released further mineral N after application. Vinasse and Biofer had almost no mineral N initially, but much of the N present mineralised rapidly. About 65% of total N in Biofer, Vinasse, and chicken manure was in mineral form within 30–50 days or 450 growing degree-days (GDD), after which net mineralisation ceased. This indicates that these three types of fertiliser should be applied at least one month before the end of crop N uptake and that autumn application is associated with a risk of N leaching unless a crop with high N uptake is present during winter.

Performance of Soil Electrical Conductivity and Different Methods for Mapping Soil Data from a Small Dataset

The performance of different methods for making soil maps from a small dataset was assessed. Soil samples obtained at five different depths were taken from 39 locations within an arable field in Sweden and analysed for clay content, soil organic matter content, pH (H2O), K-HCl, P-AL, K-AL and Mg-AL. Detailed and densely sampled soil electrical conductivity (EC) data with a distinct border between two different regions was used for dividing the field into two zones. Averages from these zones gave better prediction for most variables than interpolation without respect to the border. With the border taken into account, cokriging with EC as a covariable improved the prediction, whereas the improvement with ordinary kriging and inverse distance weighting (IDW) was insignificant. Direct interpretation of EC by a simple linear regression model gave reasonable predictions for clay content. In general, even the simplest interpolation method improved the prediction compared to field average.

Simulating site-specific nitrogen mineralization dynamics in a Swedish arable field

Abstract The objective of this work was to test whether a dynamic soil C and N model using site-specific information improved estimates of apparent net N mineralization compared with regressions only based on static soil properties. This comparison was made using data from a 34-point sampling grid within a Swedish arable field during two growing seasons, using a simple carbon balance and nitrogen mineralization model (ICBM/N) for the dynamic approach. Three free model parameters were simultaneously optimized using non-linear regression to obtain the best model fit to the data from all grid points and both years. Calculated annual mean net mineralization (Nm_sim) matched the measured Nm mean exactly, and was 44 and 71 kg N ha−1 for the two growing seasons 1999 and 2000, respectively. However, the variability in calculated Nm_sim values among the 34 grid points was smaller than that measured, and only a small proportion of the variation within a single year was explained by the model. Despite this, the model explained 56% of the total variation in Nm during the two growing seasons, mainly due to the good fit to the seasonal overall difference. Significant factors influencing net mineralization included the soil environment controlling mineralization, total N in soil organic matter and N in crop residues. Uncertainties in estimation of θ fc and θ wp (soil water content at saturation and wilting point) and the possible influence of unknown horizontal and vertical water flows made high-precision calculations of soil water content difficult. The precision and general applicability of the actual measurements thus set limits for estimating critical parameters, and the limitations of both the experimental design and the model are discussed. It is concluded that improvements in precision in sampling and analysis of data from the grid points are needed for more critical hypothesis testing.

Optimal Placement of Meat Bone Meal Pellets to Spring Oats

New technology makes it possible to apply organic fertilizers with higher precision, and organic producers want to know how to exploit these new possibilities to make their production more efficient. This study investigated the effect of band application (in different positions) of pelleted organic fertilizer, compared with broadcasting, on grain yield and weed density in spring oats (Avena sativa L.). Six microplot field experiments were carried out on silty clay and sandy loam in Sweden during the growing season of 2014-2016. In oats seeded at 25 cm row spacing, pelleted meat bone meal was band-applied at one of three distances from the crop row (0, 4, and 12.5 cm) and at two or three incorporation depths (1 and 4 cm on silty clay and 1, 4, and 6 cm on loamy sand). These treatments were compared with broadcast spreading, mineral nitrogen fertilizer, and an unfertilized control. On both soil types, fertilizer placement 4 cm from the crop and 4-6 cm incorporation depth gave the highest yield and crop nitrogen uptake. Yield in this treatment was 800 kg ha-1 higher on clay soil and 1100 kg ha-1 higher on sandy loam compared with the same organic fertilizer applied by broadcasting, an 80-150% yield increase. On the sandy loam, distance from the crop row had a more significant effect on grain yield (p<0.001) than soil incorporation depth (p=0.07). On the silty clay, crop yield was significantly influenced by incorporation depth (p=0.003) and distance from the crop row (p=0.04). In five experiments, mineral N fertilizer equivalent (MFE) increased from on average 63% with broadcasting to 85% with placement 4 cm from the crop row and 4 cm incorporation depth. Weed biomass was significantly affected by fertilizer placement on the clay soil, with higher weed biomass with deeper incorporation (p=0.045) and greater distance from the crop row (p=0.049). On the sandy loam, there was a tendency for larger weed plants at greater distance from the crop row (p=0.13) except when seeds and pellets were placed together, which gave the highest weed weight, probably due to lower competition from the crop in this treatment.