Alois Kornher

Modelling non-structural carbohydrates in forage grasses with weather data

Abstract A weather-based dynamic model was formulated to simulate the concentration of water-soluble carbohydrates (WSC) in harvestable dry matter of forage grasses. The main aim of the model development was to describe and quantify the response of photoperiod (daylength), incoming shortwave radiation, air temperature and plant-available soil water on WSC content in a simple functional approach with widely available weather data. In co-operation with a regional or national agrometeorological service, farmers can, in the future, get information about the WSC content of their herbage in order to optimize the cutting date for pastures and temporary grassland due to the demands of animal nutrition and silage management. The response of meteorological factors on WSC content was modelled in two steps. Firstly, the general trend of WSC content was calculated, describing indirect weather effects on WSC content concerning phenological development of the plants. Secondly, direct influences of weather factors on WSC content were added, reflecting photosynthesis and respiration processes on a short time scale. The modelling approach was parameterized on a set of data from northern Germany, which were collected daily in different growing periods in the years 1990, 1991 and 1994 in stands of Lolium perenne L. The model fitted the WSC content of the presented data with a mean root mean square error of 2.74% units (cv: 11.3% ). The potential of the model is discussed in relation to weather sensitivity and adaptability to different genotypes, sward types and nitrogen fertilization levels.

Predicting silage maize yield and quality in Sweden as influenced by climate change and variability

Abstract In recent decades European silage maize production has extended northwards, into Scandinavia, and the importance of maize in fodder production has increased substantially. For the northward expansion of maize production it is of interest to evaluate both the role of climate change that has occurred already, and scenarios for possible future climate change. The aim of this study was to assess for Swedish climatic conditions, the annual variation in silage maize yield and quality (dry weight and starch contents) of cultivars currently grown in Germany. The MAISPROQ simulation model currently used in German maize production was applied to evaluate the effects of (i) cultivar differences (four cultivars; four sites; 2003–2009), (ii) intra-regional variation among ten sites representing three regions (two cultivars; 2003–2009), and (iii) climatic variability among two historical periods during 1961–2009 and three future periods during 2011–2100 using A2-emission climate scenarios and the Delta-method (two cultivars; four sites). Forage quality assessments strongly influenced the assessments of harvest time and thereby the yield. Changes in simulated yield of the tested cultivars were high for the past climate, but relatively small under future climatic conditions due to earlier harvest caused by improved forage quality. By the end of the 21st century an appropriate fodder quality would be achieved every year in the south of Sweden, whereas in the middle of Sweden (60°N) about 30% of the years would not be successful, even for the earliest cultivar. In the east, increased water stress counteracted the positive effect of a prolonged growing season. It was concluded that adaptation of field experiments to model calibration requirements remains to be done, in order to enable extrapolation of observations from Swedish field trials to a changing future climate.

Über die bestimmung der strahlungsenergie im wellenlängenbereich von 0,3–0,7 μ in pflanzenbeständen

Abstract A method and equipment for measuring the global radiation in the range 0.3–0.7μ (L-radiation) in crops are described. The L-radiation is obtained as a difference from measurements with two pyranometers: one with clear glass (global radiation 0.3–3μ) and the other with a dome of RG 8 (R-radiation, 0.7–3μ). The pyranometers are moved along a horizontal track through the stand. Thereby the global and R-radiation are registered. It is shown that the relation between the transmission of the L- and R-radiation for stands of Festuca pratensis Huds , may be approximately expressed by a simple power. It is also shown how, by using this relation, the L-radiation is computed from measurements of the global radiation in and over the stand.

Crop genotype-environment modelling to evaluate forage maize cultivars under climate variability

A crop model and environmental data were used to simulate genotype-environment interactions for commercial forage maize cultivars. Genotype parameters defined by the MAISPROQ model were calibrated to observed aboveground dry matter (DM) yield and quality (concentrations of DM and starch) data from Swedish field experiments 2009–2011 on four forage maize cultivars with different maturation rates (Avenir, Isberi, Jasmic and Burli). The model calibration predictability (coefficient of determination, R2) ranged from 0.18 to 0.45 for yield and 0.40 to 0.86 for quality. The corresponding values for validation were in a similar range for the growth model but less for the quality model (0.36–0.38 and 0.25–0.54, respectively). Thereafter the model was used to assess the cultivar performance for different locations and future climate conditions. The simulated DM yield averaged for 2003–2009 varied between 5% and 25% among nine locations in Sweden due to differences in weather conditions, depending on cultivar. The proportion of years with successful harvest (34% DM concentration being achieved by 31 October) varied between 60% and 100% for the early cultivar (Avenir) and 0% and 70% for the late cultivar (Jasmic). Under future climate conditions, harvest of the early-maturing cultivar (Avenir) will occur earlier (by up to 19 days in Lund [55.6°N] and 24 days in Uppsala [59.8°N] by 2085), but with unchanged or even slightly decreased DM yields compared with current levels. The starch concentration will remain almost unchanged in Lund but increase in Uppsala, especially for the late-maturing cultivar. We regard the model predictions of quality to be reasonably satisfactory, whereas those of DM yields are less reliable due to observations for calibration being available only for the period after flowering. Therefore, more frequent sampling in the early growing season is required to improve the predictive power of the model, especially for DM yield.