Nutrient recovery, defined as the proportion of nutrients supplied that is taken up by the crop in above-ground parts, varies strongly from field to field. The general mechanisms are known, yet poorly understood in quantitative terms. Fertilizer recommendations, e.g. using QUEFTS, are based on simple rules of thumb for expected recovery fractions. These are typically derived from experiments that may not reflect on-farm field conditions very well. As such, fertilizer recommendations and expectations of crop yields are on average pretty good, yet come with large errors at farm level. Farmers may be more realistically informed about expected yield responses when fertilizer recovery is better understood, especially under poor soil fertility conditions with low yields.
In this project, we seek to better understand the mechanisms and evaluate available modelling approaches that describe plant-microbe competition and nutrient immobilization into organic matter or other pools in the soil. You will review literature and compare and test simple models to formulate hypothesis that help explain the difference between responsive and non-responsive soils. These models will be confronted with data from a long term experiment on 23 farms in Western Kenya.
He, P., S.-Z. Wan, X.-M. Fang, F.-C. Wang and F.-S. Chen (2016). "Exogenous nutrients and carbon resource change the responses of soil organic matter decomposition and nitrogen immobilization to nitrogen deposition." 6: 23717.
Ichami, S. M., K. D. Shepherd, A. M. Sila, J. J. Stoorvogel and E. Hoffland (2019). "Fertilizer response and nitrogen use efficiency in African smallholder maize farms." 113(1).
Nguyen, M. H. (2003). Modelling of K dynamics in soils and K uptake by crops. In: . PhD thesis Wageningen University. Chapter 6.
Njoroge, S., A. G. T. Schut, K. E. Giller and S. Zingore (2019). "Learning from the soil’s memory: Tailoring of fertilizer application based on past manure applications increases fertilizer use efficiency and crop productivity on Kenyan smallholder farms." 105: 52-61.
Njoroge, S., A. G. T. Schut, K. E. Giller and S. Zingore (2017). "Strong spatial-temporal patterns in maize yield response to nutrient additions in African smallholder farms." 214: 321-330.
Wolf, J., C. T. de Wit and H. van Keulen (1989). "Modeling long-term crop response to fertilizer and soil nitrogen. I. Model description and application." .
Van Duivenbooden, N., C. T. de Wit and H. van Keulen (1995). "Nitrogen, phosphorus and potassium relations in five major cereals reviewed in respect to fertilizer recommendations using simulation modelling." 44(1): 37-49.
A successful completion of the course Analysing Sustainability of Farming Systems or QUALUS. Ability to use R or a strong interest in learning it is required.
Time and Location
Tom Schut 0317-482454 email@example.com
Samuel Njoroge Samuel.firstname.lastname@example.org