Long-term effect of reduced fertilizer rate and integrated soil fertility management practices on soil properties in Sahelian West Africa
Date
2015-12-11
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ORCID
Type
Thesis
Degree Level
Masters
Abstract
Fertilizer microdosing, the application of a reduced fertilizer rate next to the seed within ten days of sowing, and other Integrated Soil Fertility Management (ISFM) techniques including organic matter (OM) application and legume incorporation have shown potential for improving crop production of smallholder farmers in the Sahel of West Africa in short-term research. Little long-term research on the sustainability of these techniques has been conducted thus far, however. The objective of the current research is to determine the long-term effect of the microdosed rate of fertilizer at the Sadore research site in Niger running 16 years, as well as the impact of ISFM techniques at both Sadore and a 50-year running site at Saria, Burkina Faso on SOM dynamics and soil properties including pH, soil organic carbon (C), cation exchange capacity, electrical conductivity, total nitrogen (N) and phosphorus (P), and available P. SOM dynamics were investigated using the X-ray Absorption Near-Edge Structure (XANES) technique for C and N speciation. Yield regression under fertilizer treatments at Sadore was also calculated. Treatments at Sadore included three rates of fertilizer: control, microdosed rate of 15 kg N ha(-1) and 4.4 kg P ha(-1), and 30 kg N ha(-1) and 13.2 kg P ha(-1) with P broadcasted and N applied using point placement. Crop residue and manure were also applied, each at 300, 900, and 2700 kg ha(-1). At Saria, ISFM treatments included two broadcasted fertilizer rates: 1) 100 kg ha(-1) 14-23-14 (NPK) with 50 kg ha(-1) urea and 2) NPK with an additional 50 kg ha(-1) urea and 50 kg ha(-1) KCl, with and without crop residue at 4800 kg ha(-1), or manure at 5000 kg ha(-1) or 40000 kg ha(-1). As well, mixed cereal-cowpea cropping was compared to continuous cropping of millet at Sadore and sorghum at Saria. The microdosed rate at Sadore had significant yield benefits over the unfertilized soil; however, yield declined over time under both the microdosed and recommended fertilizer rates. Possible soil fertility-related drivers of yield decline include soil acidification, low SOM, and mining of nutrients not applied in fertilizer. Soil pH was improved with crop residue at the 2700 kg ha(-1) rate at Sadore and manure at the 40000 kg ha(-1) rate at Saria, which also increased SOC and CEC. C and N XANES data showed that soil treated with higher OM rates and reduced or no fertilizer was more enriched in aromatic-C, pyrrolic-C, N-bonded aromatics and amide-N, organic groups associated with lower levels of SOM degradation and/or greater input of available microbial substrate, and depletion of ketone- and phenol-C groups under continuous cropping also indicated greater levels of SOM breakdown. For sustainable soil fertility management in the Sahel, applying the microdosed rate of fertilizer with manure and crop residue at as a high of rates as possible for smallholders, and including legumes into the cropping mix is recommended.
Description
Keywords
Soil fertility, Sahel, long-term sustainability, fertilizer microdosing, integrated soil fertility management, soil organic matter dynamics, XANES, NEXAFS
Citation
Degree
Master of Science (M.Sc.)
Department
Soil Science
Program
Soil Science