Transformation of the Hyper-Arid Desert Soils in Arequipa Peru During Four Decades of Irrigated Agriculture

Lucia Zuniga, Purdue University

Abstract

The growth in the human population increases the global demand for food. However, in countries with limited arable land and abundant water, it means expanding into marginal lands or fragile ecosystems and mining non-renewable water resources to meet that demand. Converting deserts into productive agriculture heavily depends on distant water supplies and efficient irrigation methods. In Peru, nearly 32 million people rely heavily on human-made coastal irrigation agricultural hubs that rely on water from melting glaciers, snowpack, and rain transported by rivers and canals from high in the Andes. However, Peru’s water resources are in a vulnerable state as climate change has shifted rainfall patterns causing glacier retreat affecting nearly the loss of onethird of the glaciers. In recent decades, an increase and expansion of irrigation projects in Peru require agriculture practices to consider environmental impacts directly. Now is the time to explore the sustainability of the desert agroecosystems and understand how different water management practices influence the supporting soil’s health so decision-makers can plan for future change in water resources and any feedbacks to the productivity of the soils. The increase in the global population, changing food and goods consumption patterns, and the expansion of irrigated agriculture has drastically increased the global demand for freshwater. In many parts of the world, there are significant spatial and temporal variations between the demand for water for irrigation and cities and its availability, leading to severe water scarcity. In some of these places, a large percentage of national populations rely on water sources like glacial melt, distant high mountain precipitation, and snowpack, which are also disappearing at an alarming rate due to a regional warming climate. In the nation of Peru, these challenges converge 65 % of Peru's 33 million people live where there is only 5% of the nation’s water supply. Over the past 40 years, Peru has led some of the largest scale water management projects on earth to convert infertile coastal desert soils into irrigated agricultural land. Still, these efforts can come at a severe local cost with impacts to groundwater quality, salination of the soil, toxic concentrations of trace metals due to evaporation, and overuse of fertilizer and pesticides. This thesis presents a study to assess how drip irrigation impacts desert soil chemistry within one of Peru’s desert irrigation projects in Arequipa’s southern district. We explored a chronosequence of drip irrigation in vineyards of 9-, 16- and 35- years. Results showed that both soil carbon and salinity accumulated progressively over time but that spatial accumulation patterns were influenced by proximity to the irrigation drip line. By 35 years, salinity levels exceeded what would be tolerances for most crops. Trace metals, such as Mn, Zn, and Ni, increased with time under drip irrigation and have significant relationships with Fe, present in the highest concentrations, seemingly controlling the patterns due to co-precipitation. However, no trace metals were found in quantities that would exceed Peru’s limits for agricultural soils. While drip irrigation is considered a water conservation strategy and widely promoted in the region over other irrigation techniques like high water volume furrow irrigation, its use may accelerate localized negative impacts to surface soil health. These progressive changes highlight the need for effective monitoring and salinity mitigation strategies in the region. This project is part of the bilateral technical program between Purdue University and Universidad Nacional San Agustín (UNSA) called the Arequipa Nexus Institute for Food, Water, Energy, and the Environment.

Degree

M.Sc.

Advisors

Filley, Purdue University.

Subject Area

Agriculture|Climate Change|Agronomy|Aquatic sciences|Civil engineering|Geomorphology|Hydrologic sciences|Latin American Studies|Meteorology|Soil sciences|Water Resources Management

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