Ngoro: an indigenous, sustainable and profitable soil, water and nutrient conservation system in Tanzania for sloping land

Abstract

The Matengo people, in SW Tanzania, developed the ngoro conservation system several hundred years ago and it is a very effective indigenous manual cultivation practice for steep slopes. It deserves wider recognition and investigation to gain a quantitative understanding of the conservation system processes and its management to see whether it can be adapted to be more cost effective with limited land and labour resources. The objective of the study was to evaluate the effects of pit size in the ngoro cultivation system on soil water conservation and yield of maize (Zea mays L.). A field experiment was conducted in 1995/1996 at two sites near Lipumba village on the Matengo highlands in Mbinga District, Ruvuma Region, in southern Tanzania. The ngoro comprise a matrix of pits with surrounding bund walls and this indigenous system is used extensively on the steep slopes (typically 20–50%) of Mbinga District. Grass is cut prior to cultivation and laid out in a matrix, traditionally about 1.5m×1.5m square, soil is then dug from the middle of each square and placed to cover the cut grass to form four bunds surrounding each pit. Crops are planted on these bund walls (ridges), under which buried decomposing plant residues provide nutrients and also ingeniously allow seepage of excessive water across the ngoro system. The ngoro pit size treatments comprised N1 (1m×1m),N1.5 (1.5m×1.5m) and N2 (2m×2m) laid in a randomised complete block design with four replications. Although ngoro profiles were degraded over time, the net loss of soil from the system was negligible as the majority of soil was redeposited in the pit. N2 was found to be the most suitable pit size on steep slopes. Pit size did not significantly influence the soil moisture regime as measured in this study. Increase in pit size generally resulted in decreased soil penetration resistance and improved plant growth resulting in the highest grain yield being obtained from the 2m×2m ngoros. Increasing the pit size reduced labour input requirements and thereby markedly boosted the profitability of the system.