Nutrient response and nutrient retention efficiency and free-living N₂ fixation in large-scale oil palm plantation with different agricultural management practices

My research focuses on the effects of management practices on the efficiency with which soil nutrients are used and retained in oil palm plantations in the province of Jambi, Sumatra. The traditional management practices in the studied plantation are high rates of fertilization and herbicides application, and these practices resulted in high nutrient losses both via gas emissions and leaching. I investigate if reduced fertilization rates and manual weeding could result in higher nutrient retention efficiency and decreased nutrient losses, without decreasing the yield of the plantation. The research will have fertilization rate (i.e. conventional and reduced) and weeding (i.e. herbicide application and manual) as treatments, resulting in four treatments combinations.
I will study how nitrogen is used and retained in the soil by assessing:

• Nutrient response efficiency = yield / plant available N
• Nutrient retention efficiency = 1 - (leaching losses / N availability in the soil)
• Rates of free-living N₂ fixation in the soil

These parameters will be analyzed in three different sampling spots that have been selected in order to characterize the spatial variability associated with the agricultural practices: the fertilized area around the palm at 1m distance from the palm base, the unfertilized area between palm rows and below the frond stacks on the inter-rows.