Jørgen Berntsen

Comparison of methods for simulating effects of nitrogen on green area index and dry matter growth in winter wheat

Abstract Crop simulation models are increasingly being used to simulate the response of crop production to variation in input use. Current and widely used crop models differ strongly in the way in which green area index (GAI) and radiation use efficiency (RUE) is affected by nitrogen (N) supply. Three different methods of simulating effect of N on development of GAI were tested in combination with three different methods of simulating effects of N on RUE. The methods tested represent functions applied in three existing wheat simulation models: FASSET, Sirius and DAISY. GAI depends in FASSET on crop dry weight, temperature and N uptake, in Sirius on temperature and N uptake, and in DAISY GAI depends on dry weight and temperature. Sirius has no effect of N on RUE, DAISY uses a segmented linear response function, and FASSET uses a curvilinear response. The different methods were implemented in the FASSET model framework, and maximum RUE at optimal N supply was calibrated for each model combination using 4 years of growth analysis data from an experiment in winter wheat with three rates of mineral N fertiliser at Research Centre Foulum, Denmark. The model combinations were validated using 2 years of growth analysis data from an experiment at Research Centre Foulum with different timing of N application. The model combinations were tested against grain yield response to increasing N supply from a series of N fertiliser experiments in Denmark. The observed development of GAI and dry weight over time in the calibration and validation data sets could be reproduced by all combinations of GAI and RUE models. This shows that a large variation in N supply rates is more important than detailed sampling over time when validating and testing crop response to N supply. The observed response of grain yield to increasing rates of mineral N fertiliser could be reproduced by most of the model combinations. However, the yield increase was overestimated with the use of a segmented linear response of RUE to N supply, and the optimal N rate was underestimated when the N response of RUE was ignored.

Estimated N leaching losses for organic and conventional farming in Denmark

The impact of organic compared to conventional farming practices on N leaching loss was studied for Danish mixed dairy and arable farms using an N balance approach based on representative data. On mixed dairy farms a simple N balance method was used to estimate N surplus and N leaching loss. On arable farms the simple N balance method was unreliable due to changes in the soil N pool. Consequently, the FASSET simulation model was used to estimate N surplus, N leaching loss and the changes in the soil N pool. The study found a lower N leaching loss from organic than conventional mixed dairy farms, primarily due to lower N inputs. On organic arable farms the soil N pool was increasing over years but the N leaching loss was comparable to conventional arable farms. The soil N pool was primarily increased by organic farming practices and incorporation of straw. The highest increase in the soil N pool was seen on soils with a low level of soil organic matter. The level of N leaching loss was dependent on soil type, the use of catch crops and the level of soil organic matter, whereas incorporation of straw had a minor effect. N leaching was highest on sandy soils with a high level of soil organic matter and no catch crops. The study stresses the importance of using representative data of organic and conventional farming practices in comparative studies of N leaching loss.

Simulating trends in crop yield and soil carbon in a long-term experiment—effects of rising CO2, N deposition and improved cultivation

Measurements of crop yield and soil carbon in the Bad Lauchstädt long-term fertiliser experiment were analysed with the FASSET model. The model satisfactorily predicted yield and soil carbon development in four treatments: no fertiliser, mineral fertiliser, farmyard manure and farmyard manure plus mineral fertiliser. However, there was a residual between the observed and simulated yield, which was correlated with year. This could be attributed to an increase in observed yields during the last six decades. Scenario analysis showed that the most probable explanation for this yield increase was the use of new crop varieties and/or pesticides, while the increase in atmospheric CO2 and changes in local N deposition were of lesser importance. The rise in CO2 thus only explained 9–37% of the yield increase. The observed and simulated developments in soil carbon were quite different in the four treatments. However, the changes within each treatment for different scenarios were much smaller than the substantial difference between treatments. Thus, it was concluded that the type of nutrient applied was more important than development in CO2 concentration or N deposition in determining soil carbon.

Simulating residual effects of animal manures using 15N isotopes

An estimation of the residual nitrogen effects of animal manure is important when optimizing crop rotations and fertiliser applications. The residual effect of animal manure was studied with the dynamic simulation model FASSET. The model was tested on experiments with 15N-labelled animal manures, where the fate of labelled manure N had been studied. Three field experiments differing in animal manure type, the labelled fraction of the manure, soil type and application techniques were analysed. The duration of the experiments varied between one and three years. In general, the model simulations agreed well with the observations. At the end of the experimental periods, the model captured 74% of the observed variation in soil 15N, whereas some systematic difference was found between measured and simulated plant uptake of 15N. The model was used to evaluate the impact of soil types, soil fertility, manure type, climate and crop type on the 15N residual effect of animal manure. These scenarios showed that wet climates, sandy soils and crops with a short growing season reduce the residual effects of animal manures. The type of the manure also influenced the residual effect of the manure such that the residual effect increased from pig slurry and cattle slurry to deep litter. The soil organic matter level had little influence on the 15N residual effect of the manure.

Performance of spring barley varieties and variety mixtures as affected by manure application and their order in an organic crop rotation

Abstract In order to obtain a high and stable yield of organic spring barley, production should be optimized according to the specific environment. To test the performance of spring barley varieties under varying cropping conditions, a field experiment was carried out in 2003 and 2004 in a six-field mixed organic crop rotation. We investigated the choice of variety, the order in a rotation, and the application of manure (slurry and farmyard manure; 0 to 120 total-N ha−1) on grain yields of six selected varieties with different characteristics grown in either pure stands or in two spring barley mixtures, each consisting of three varieties. Average grain yield of the barley varieties varied between 3.3 t DM ha−1 and 4.1 t DM ha−1. Grain yields of the two mixtures were 4.0 and 3.6 t DM ha−1, respectively. The varieties/mixtures interacted with crop order and year. Foliar diseases were more severe in the barley following grass-clover with large annual differences in the individual diseases. Despite different rooting depths and nutrient uptake patterns, there was no interaction between variety/mixture and the manure input regarding grain yield. In the 1st year after grass-clover, one of the two mixtures gave higher grain yield than the average yield of the individual varieties in the mixture. This was not the case in the 4th year after grass-clover and for the second variety mixture. Thus, although the present results did not indicate that some barley varieties were better adapted to conditions with low manure input than others, variety mixtures that give a robust and stable organic production may potentially be developed.