Cropping system and altitude as drivers of soil Macrobiota and nutrient variability for arabica coffee production in mount Elgon region

Abstract

There is need to produce sufficient food and fuel for the growing population without damaging the ecosystem services. In Uganda, highlands have inherent fertile soil but are rapidly losing quality due intensification. Farmers utilize various management adaptations such as agroforestry systems with other on-farm soil, pest and disease management practices to increase production. A study was carried out to determine how different coffee cropping systems at varying altitudes influence occurrence of the soil dwelling coffee root mealybugs, nutrient cycling macro-fauna, soil nutrients, microclimate, and yield of coffee in the Mt. Elgon Region (MER) of Uganda. The factors investigated were altitude and cropping systems. Three levels of altitude were considered namely; i) low (1300-1499 meters above sea level (m.a.s.l), ii) mid (1500-1679 m.a.s.l) and iii) high (1680-2100 m.a.s.l). Cropping system was demarcated into four categories; i) Coffee monocrop, ii) Coffee-annual crop, iii) coffee-banana, and iv) coffee-banana-shade trees, which were nested within the altitude categories. Data was collected on longitudinal basis on abundance of root mealybugs (Pseudococcidae), ants (Formicidae), millipedes (Diplopoda), and earthworms (Lumbricidae) in the fields. Ambient temperature and relative humidity were obtained on a monthly basis in the study fields. Soil temperature and moisture were taken in situ using sensors. Composite soil samples from the fields were taken for analysis of selected physical and chemical properties. Results showed that cropping system, altitude and their interaction significantly influenced the occurrence of the arthropods in the different functional groups. Soil macrofauna were greatly influenced by cropping system and altitude; earthworms preferred the cooler and more diversified cropping systems while millipedes were common in nitrogen richer soils. Root mealybugs were more severe in coffee monocrops than in shaded systems. The coffee-annual crops systems had low abundance of soil macrofauna, nutrients, high severity of the root mealybug and relatively warmer microclimate. Coffee systems intercropped with shade trees and bananas had cooler temperatures and higher relative humidity. It was noted that more diverse intercrops gave higher coffee berry yields, even at higher altitudes. Diversified coffee systems had enriched soil biota, higher concentrations of soil organic matter and total nitrogen and high moisture content and low soil temperature. This showed that the diversified coffee systems were more linked to soil conservation and productivity, which is crucial in highland areas like the Mt. Elgon region.