Crop nitrogen demand and canopy area expansion in winter wheat during vegetative growth

The effect of nitrogen (N) on crop growth and productivity is mediated through effects on both light interception (green crop area) and radiation use efficiency (RUE). The effects of N nutrition on these factors were studied using data on green area index (GAI), above-ground dry matter and N uptake from growth analysis measurements in winter wheat from a number of experiments in Denmark with different application rates of N. Only measurements taken prior to anthesis were used in the statistical analyses. The N uptake was found to be proportional to GAI, and to have an additional curvilinear response to dry matter implying decreasing N concentration with increasing dry matter. This supports the hypothesis that nitrogen is associated with both the green surfaces of the crop canopy and with the dry matter component. A model of GAI expansion is presented incorporating three limiting factors: an exponential increase in GAI in thermal time, a minimum leaf area ratio, and a minimum ratio of GAI to N content in above-ground dry matter. This simple function has potential to be used as a tool for targeting timing and rates of N fertilisation in relation to a desired development of GAI. Such N application strategies should also consider the nitrogen nutrition index (NNI), which was defined based on the relationship between N uptake and both GAI and dry matter. The response of RUE to NNI showed a curvilinear response with a tendency for saturation at high NNI. The design of N application strategies should therefore ensure that low NNI is avoided during the most productive periods in the growing season.     

Long-term fate of nitrogen uptake in catch crops

The long-term effects of undersowing a ryegrass catch crop in cereals was analysed with the FASSET simulation model. The model was tested on a 28-year field experiment with ryegrass catch crops in spring barley. The experiment included treatments with nitrogen (N) fertiliser rates, catch crop use and timing of tillage. The modelled effects of these treatments generally agreed with observations on crop production, soil carbon, soil nitrogen and nitrate leaching. Both the observations and the simulations predicted a yield increase of 7 kg N ha⁻¹ and an increase in nitrate leaching of 13 kg N ha⁻¹ due to a prehistory of 24 years with continuous use of catch crops compared to a prehistory without catch crops.

A range of scenarios was constructed to evaluate the fate of the reduced nitrate leaching on crop N uptake, N leaching, gaseous emissions and change in soil organic N, and how this fate interacts with soils and climate and management. These scenarios showed that 22–30% of the reduced nitrate leaching was subsequently leached during the following decades after termination of catch crop use. Between 35 and 40% of the reduced nitrate leaching was harvested in cereals. The exact distribution depended primarily on the soil texture. The scenarios showed that effects of catch crops should be evaluated on the long-term rather than consider short-term effects only.     

Artificial light sources and their influence on physical activity and energy expenditure of laying hens

1. The influence of fluorescent and incandescent artificial lighting in a 16L:8D day/night schedule on number and intensity of movements, and on total, resting and activity‐related energy expenditure was investigated.

2. Fluorescent light showed the same positive correlation between light intensity and physical activity at all activity levels as was found previously for incandescent light.

3. Light‐dependent physical activity under fluorescent light was higher than under incandescent light at illuminances of 5 lux and above, indicating the fowl's ability to perceive qualitative light differences.

4. Total and activity‐related energy expenditure were positively associated with illuminance; resting energy expenditure was not influenced.

5. Total, resting and activity‐related energy expenditure were not statistically significantly different between light sources.

6. The results are discussed in relationship to Teichmuller's concept of adequate lighting and the characteristics of the fowl's visual system.