Börje Lindén

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.

NIR spectroscopy, mineral nitrogen analysis and soil incubations for the prediction of crop uptake of nitrogen during the growing season

To predict the amount of N taken up in above-ground plant parts during the growing season, initial mineral soil N, a soil incubation method, soil organic matter and NIR data were compared as predictors. Soil samples were taken from 15 plots cropped with winter wheat on a farm in south-western Sweden. The plots were not fertilized with N during the 1997 growing season. N contents in above-ground plant parts were measured in mid-June and in mid-August. All methods were capable of predicting the crop uptake of N reasonably well. NIR data gave at least as good predictions as the best traditional method, initial soil NO3-N. The most important wavelengths, around 1400 and 1700 nm, and above 2000 nm, coincide with the wavelengths reported earlier to be important for the prediction of soil organic matter. However, the data suggest that other soil components influencing mineralization are also spectrally active. Since very few samples were taken, the studies need to be extended in order to be able to use the method in practice. It is recommended that further studies be instigated for the possibility of using the same NIR calibration over several years and to clarify the spatial regions that the calibrations can cover.

Reducing nitrate leaching after winter oilseed rape and peas in mild and cold winters

Nitrate leaching after winter oilseed rape and peas has not been studied at the most northern limits of oilseed rape cultivation where winters vary between being mild, with continuous drainage, and cold, with periods of frozen soil. Here, we studied the effect of N fertilisation to oilseed rape, catch crops after oilseed rape and peas and dired drilling of winter wheat after oilseed rape on N leaching in south-west Sweden. Nitrate leaching was determined in two field experiments, dated 2004–2006 and 2005–2007, respectively, on a sandy loam. Our results show that under oilseed rape nitrate leaching was low, at 16–23 kg N ha−1, in a mild winter with drainage from October to March. In the subsequent mild winter nitrate leaching under wheat was higher, amounting to 35–94 kg N ha−1. Nitrate leaching levels were similar, 32–58 kg N ha−1, for all crops in a cold winter with a long-lasting snow cover and main drainage occurring after snowmelt in March and April. Application of fertiliser N to oilseed rape at the optimum N rate, rather than 50 kg N ha−1 above optimum, reduced leaching in a following winter wheat crop by 25 and 27 kg N ha−1 in a cold and a mild winter, respectively. Spring undersowing of perennial ryegrass as a catch crop reduced leaching by 12 kg N ha−1 after optimally fertilised oilseed rape in a mild winter, despite only growing until mid-September when winter wheat was sown. An undersown catch crop of peas, then grown until November, reduced leaching by 15 kg N ha−1. Direct drilling of winter wheat after oilseed rape had no effect. These findings show that there are risks of enhanced leaching in early spring after a cold winter with a snow cover and superficially frozen soil. Optimising the spring N rate for oilseed rape was the most effective measure to decrease leaching in both mild and cold winters, and this effect was improved by an undersown catch crop in a mild winter.

Simulated and measured nitrogen conditions in a manured and fertilised soil

The governing factors for soil nitrogen dynamics were identified with a simulation model. In addition, the model was used to interpret measurements from a plot fertilisation experiment in southwest Sweden.Simulated moisture and temperature conditions were the driving variables for the simulation of soil nitrogen dynamics and leaching during a 6-year period. The results of the simulation were compared with monthly observations on two plots with grain crops, one with liquid manure and commercial fertilisers applied and one with commercial fertilisers only.Simulated temporal variations of the nitrate and ammonium storages generally agreed with observations. The dominant role of the crops as a determinant of soil nitrogen conditions was demonstrated. A higher leaching loss from the plot with application of commerical fertilisers only occurred both in simulations and measurements compared to the plot with application of both commercial fertilisers and manure. The main reason was the higher N-application in the former treatment.The effect of water flows in macropores was interpreted as a delay of simulated leaching compared to observed leaching on some occasions in summer and early autumn. No direct effect of the macropores on the yearly rates of leaching could be seen.

Enset farming in Ethiopia. I. Soil nutrient status in Shoa and Sidamo regions

Abstract Soil samples were collected from farms in two enset (Ensete ventricosum) growing regions of Ethiopia and analyzed for plant nutrients. For comparative reasons, soil samples were taken both from fields where enset had been continuously cultivated for several decades and from other fields: annual cropping, grazing, or uncultivated. The results reveal that the enset fields studied had higher soil organic matter contents and better nutritional status than fields used otherwise, not only in the topsoil but also in the subsoil. This indicates more sustainable cultivation with maintained fertility in the enset fields. Possible explanations of this are discussed.