Paul L. G. Vlek

Learn More
Article history: Received 29 January 2008 Received in revised form 10 April 2008 Accepted 12 April 2008 This paper presents the concept and theoretical specification of a multi-agent based model for spatio-temporal simulation of a coupled human–landscape system. The model falls into the class of all agents, where the human population and the landscape(More)
For over a hundred years shifting cultivation with slash-and-burn land preparation has been the predominant type of land use by smallholders in the Bragantina region of the Brazilian Eastern Amazon. This study contrasts the nutrient balance of slash-and-burn agriculture with a fire-free cultivation. Therefore, one half of a 3.5-year-old (28.7 t DM ha–1) and(More)
Soil organisms play a central role in the decomposition of organic matter. The activity of soil organisms was comparatively examined in three experimental sites in central Amazonia (Brazil): a peach palm monoculture (Bactris gasipaes) a, rubber tree plantation (Hevea sp.), and an agroforestry system (four tree species planted in rows, the space between(More)
The N2 fixed by Azolla before and after urea application during the rice cycle, the mineralisation of Azolla-N as well as its availability to rice was studied in two greenhouse experiments conducted in 1996 and 1997 and in June 1998 in Goettingen (Germany). Dry matter production of the various rice parts of experiment 1 showed a clear positive synergism(More)
We evaluated the temporal variation of microbial biomass C, β-glucosidase, acid phosphomonoesterase (acP), alkaline phosphomonoesterase (alP), and protease activity over 18 consecutive months. The likely causes for the seasonal variability at a non-degraded and a degraded site in south-western Nigeria were identified. Microbial biomass, alP, and(More)
Soil salinity in the Aral Sea Basin is one of the major limiting factors of sustainable crop production. Leaching of the salts before planting season is usually a prerequisite for crop establishment and predetermined water amounts are applied uniformly to fields often without discerning salinity levels. The use of predetermined water amounts for leaching(More)
African farmers have relied traditionally on fallowing for up to 15 years to restore soil fertility. Leaving land unproductive for such periods is a luxury many regions cannot afford, given the contemporary decline in per capita food production (1%/year). Thus, alternative soil fertility maintenance measures such as agroforestry, novel intercropping(More)
Research was conducted at two sites located in medium and low altitude zones in eastern Uganda. The aim of the study was to evaluate the benefit of Velvet bean (Mucuna pruriens) and inorganic N fertilizer in improving maize production in contrasting agro-ecological zones over two seasons. The medium altitude zone (Bulegeni) is a high-potential agricultural(More)
This study was aimed at quantifying soybean (Glycine max) nitrogen fixation under reduced tillage (RT) and conventional tillage (CT) in a tropical Ferralsol of the sub-humid zone of western Kenya, using the isotope N dilution method. Crop residue (CR) management was a superimposed treatment in soybean-maize rotation and intercropping systems. This study(More)