Soil Nutrient Dynamics under Long Term Application of Mineral Fertilizer Micro-Dosing to Pearl Millet [Pennisetum Glaucum (L)] on a Sahelian Sandy Soil of Niger Republic

Abstract

Low soil fertility and insufficient rainfall are the major constraints limiting pearl millet yields in Niger. Thus, to address these striking constraints, institutions working in Sahel joined forces through a collaborative research programme and developed an effective technique known as fertilizer micro-dosing (application of small doses of fertilizer in the hill of the target grain crop at planting) in order to tackle these issues. Reports from the implantation of the technology have shown up to 120% of yield increase. However, the question is whether the application of this technology would not lead to soil nutrients mining in the long-term. A study was set at ICRISAT which aims at evaluating the sustainability of the technology in the long-term with regard to pearl millet productivity and with emphasis on soil nutrient dynamics. As a long-term experiment, the study started since 2008 and was laid out in a randomized complete block design that involved two pearl millet varieties, three planting densities, and four nutrients management options. For the purpose the present research, a sub-set of the treatments from this long term experiment was used. The nutrient management options considered include the control, 2kg.ha-1 of DAP+ 1kg.ha-1 of Urea at elongation stem period, 30 kg. ha-1 of NPK and 60 kg. ha-1 of NPK. Soil survey was carried out in each of the corresponding plots, soil samples were collected both between and on the planting hills. A total of 36 soil samples were collected and analyzed at Soil Lab of ICRISAT-Sahelian Centre Sadore. The results showed significant decline in soil nutrient over years. The change in soil nutrient was markedly different on the planting hills and that from between hill spaces. The change in soil pH-H2O values on the planting was -7.06% for the control plots and -9.57% for the plots treated with NPK. Hence, this negative change resulted in possible acidification of the experimental site. The total nitrogen content dropped in both the control plots and the plots that received NPK as micro dose. The percentage of change decreased with the application of NPK microdosing on the planting hills with respectively -5.11% and -12.45% in the control plots and the plots receiving NPK. Positive significant change in available P was observed (P≤0.05%) in soil between hill with 1.08% in the control plots and 15.97% in the plots amended with NPK. Whereas on the planting hills, the change was higher in plots treated with NPK compared to the control plots with respectively 88.19% and -6.27%. Further, the trend of the change observed in soil organic carbon content on the planting hills was -21.85% and -26.71% in micro-dosing plots and in the control plots respectively. Both stover yield and total biomass showed similar trend in which decreased yield was obvious over the years. In 2009, Average stover yield of 4053 Kg. ha-1, 5867 Kg. ha-1, 6667 Kg. ha-1 and 5360 Kg. ha-1 was obtained respectively for the control plots, 2g DAP +1g Urea plots, 3g NPK plots and 6g NPK plots. Whereas in 2010, the stover yield decreased by 31%; 18.47%; 13% and 26.12% respectively for the control plots, the plots applied with 20Kg.ha-1of DAP plus 10Kg. ha-1 of Urea, 30Kg.ha-1 of NPK plots and 60Kg.ha-1 of NPK. Grain yield also dropped in 2010 compared to 2009 by 36% for the control plots, 62.6% for the plots applied with 20Kg. ha-1 DAP plus 10 Kg. ha-1 Urea and 43.65% for the plots applied with 60Kg. ha-1 of NPK. These findings showed that in the Sahel low-input based millet cropping systems, for the micro-dosing fertilizer technology to be sustainable in the long term, the improvement and maintenance of soil fertility should be considered as the cornerstone.