Effect of Zai Soil and Water Conservation Technique on Water Balance and the Fate of Nitrate from Organic Amendments Applied: A Case of Degraded Crusted Soils in Niger

Abstract

Experiments were conducted on degraded crusted soils to study water status and nitrogen release in the soil during the dry seasons of 1999 at ICRISAT research station and on-farm during the rainy seasons of 1999 and 2000 in Niger. Zai is a technology applied on degraded crusted soil, which creates conditions for runoff water harvesting in small pits. The harvested water accumulates in the soil and constitutes a reservoir for plants. The organic amendment applied in the Zai pits releases nutrients for the plants. Soil water status was monitored through weekly measurement with neutron probe; access tubes were installed for the purpose. Nutrient leaching was measured as soil samples were collected three times throughout the cropping season. A rapid progress of the wetting front during the cropping period was observed. It was below 125 cm in the Zai-treated plots 26 days after the rain started versus 60 cm in the non-treated plots. Applying cattle manure leads to shallower water profile due to increased biomass production. Total nitrate content increased throughout the profile compared to the initial status, suggesting possible loss below the plant rooting system due to drainage, which was less pronounced when cattle manure was applied. This study shows that the system improves soil water status allowing plants to escape from dry spells. However, at the same time it can lead to loss of nutrients, particularly nitrogen.