Impact of tillage and nitrogen fertilization on yield, nitrogen use efficiency of tef (Eragrostis tef (Zucc.) Trotter) and soil properties

A 3-yr (2003–2005) study was conducted to assess the effect of two tillage methods: conventional tillage (CT, with four ploughings using a traditional plough, maresha) and minimum tillage (MT, with a single pass prior to sowing) and of N-fertilization, on tef yield, nitrogen use efficiency (NUE), weed infestation and soil properties at two locations in the rainfed semiarid conditions of Ethiopia. The experimental design was a split plot with three replications, with tillage treatments as main plots and N-rates as subplots. The N-fertilization rates were 0 kg N ha−1 (ZN), 30 kg N ha−1 (LN), 60 kg N ha−1 (MN) and 90 kg N ha−1 (HN). The minimum tillage practice produced as high yields as conventional tillage. Both total dry matter (DM) and grain yields were increased by N-fertilization. At both locations and in all years, there was a linear increase in dry matter production when N was increased from ZN to HN. The grain yield showed a similar increasing trend up to MN level but decreased from MN to HN. Available moisture content was relatively higher for minimum till (MT) than for conventional till (CT). In the dry years of the 2003 and 2004 cropping seasons, the average available moisture content in the plough layer was higher in MT than in CT by 0.004 m (2003) and 0.003 m (2004). Weed infestation was significantly higher in MT than in CT, with weed numbers 96 higher and weights 102 g m−2 higher in MT. Nitrogen use efficiency decreased with increased N but was not affected by tillage methods. Average N recoveries for CT and MT were generally similar (about 43%). Nitrogen fertilization significantly affected the soil total N and C/N ratio at lower depth (0.15–0.30 m). Average total N at the lower depth increased by 35.2 kg ha−1 yr−1 (203%) when N application rate was increased from MN to HN, suggesting that higher N levels are to be avoided to reduce excessive leaching to lower depths. Thus, the adoption of MT in the semiarid conditions could benefit soil and moisture conservations and reduce costs for resource poor farmers in Ethiopia without significantly affecting yield.