Joost Brouwer

Bio: Joost Brouwer is an academic researcher. The author has contributed to research in topics: Nutrient management & Agriculture. The author has an hindex of 1, co-authored 1 publications receiving 114 citations.

Science in agroforestry

Abstract: Agroforestry research is being transformed from a collection of largely descriptive studies into more scientific approaches, based on process-oriented research. The development of agroforestry as a science should be based on four key features: competition, complexity, profitability and sustainability. Managing the competition between trees and crops for light, water and nutrients to the farmers’ benefit is the biophysical determinant of successful agroforestry systems. Simultaneous agroforestry systems are more susceptible to competition than sequential ones. A tree-crop interaction equation helps quantify competition vs. complementary effects on fertility. Alley cropping, a simultaneous agroforestry system, has limited applicability because the competition factor usually exceeds the beneficial fertility effects. The Faidherbia albida parkland, another simultaneous system, is almost always beneficial since the reverse phenology of F. albida minimizes competition while enhancing the fertility effect. Sequential systems such as relay intercropping and improved fallows also minimize competition but the processes responsible for crop yield increases are largely unquantified. New methodologies for reliably measuring complex below-ground interactions are being developed.

Soil Fertility in Africa Is at Stake

Abstract: Soil fertility in Africa is under pressure as an increasing number of farmers attempt to make a living based on what the land can offer to growing plants. Studies in Africa from about 1989 have focused on different spatial scales, i.e., subcontinental, subnational, and farm. This chapter reviews the results obtained at these three levels and compares methodologies and implications. For N, annual depletion was recorded at all levels at rates of 22 kg ha−1 (sub-Saharan Africa), 112 kg ha−1 (Kisii District, Kenya), and 71 kg ha−1 (average for 26 farms in Kisii, Kakamega, and Embu Districts). If the soil nutrient balance is to become a suitable land quality indicator for wider use as a policy instrument, increased sophistication is required, including data on soil nutrient stocks and availability. The advantage of the nutrient balance approach over traditional rate-response research on fertilizers is that it includes all possible nutrient flows at the spatial scales discussed. A drawback, however, is the lack of hard data on flows that are difficult to measure (leaching, gaseous losses, and erosion), and the fact that the balance comprises several inputs minus the sum of several outputs. Nonetheless, the message comes out clearly that improved soil nutrient management is crucial for maintaining and improving soil productivity in Africa.

Soil improvement by trees in sub-Saharan Africa

Abstract: Trees can influence both the supply and availability of nutrients in the soil. Trees increase the supply of nutrients within the rooting zone of crops through (1) input of N by biological N2 fixation, (2) retrieval of nutrients from below the rooting zone of crops and (3) reduction in nutrient losses from processes such as leaching and erosion. Trees can increase the availability of nutrients through increased release of nutrients from soil organic matter (SOM) and recycled organic residues.