Optimizing Tillage and Irrigation Requirements of Sorghum in Sorghum-Pigeonpea Intercrop in Hamelmalo Region of Eritrea

Sorghum (Sorghum bicolor L. Moench) is cultivated as monocrop in Eritrea. Efforts were made to grow sorghum-pigeonpea (Cajanus cajan L. Millspp.) intercrop on the tillage, fertilizers and supplementary irrigations necessary for sorghum. Experiments were conducted in terraced fields at Hamelmalo during 2013-15 to evaluate growth and yield of sorghum-pigeonpea intercrop in split plot design with conventional tillage (CT), reduced tillage (RT) and zero tillage (ZT) in main plots and rainfed (I0), 50% of full irrigation (I1), 75% of full irrigation (I2) and 100% of full irrigation (I3) in subplots. All irrigations were stopped 15 days before sorghum maturity. Full irrigation was 60 mm applied at 50% depletion of available soil water in 1 m profile. Sorghum growth was faster than pigeonpea until 85 days from planting and pigeonpea growth accelerated only after sorghum harvesting. About 80% of sorghum roots were within 0.6 m profile but more than 75% of pigeonpea roots were below 0.60 m depth. This showed a weaker competition between the two crops for nutrients, water and light. Both grain and stover yields of sorghum were optimum in RT + I2 during the 2 years. Highest grain yield was 6900 kg·ha-1 in RT + I3 in 2013, which was at par with that in RT + I2. Mean residual soil moisture at sorghum harvesting was 74 mm·m-1, which decreased to 8 mm·m-1 by pigeonpea harvesting. Residual moisture was more in the irrigated than non-irrigated plots. Pigeonpea yields were optimum (1363 kg·ha-1) in RT + I3 and lowest (297 kg·ha-1) in ZT + I0. Average water use by sorghum-pigeonpea was 374 mm by sorghum harvesting and 438 mm by pigeonpea harvesting, producing total sorghum equivalent yield of 7475 kg·ha-1. This raised average water use efficiency from 12.6 kg·ha-1·mm-1 at sorghum harvesting to 17.1 kg·ha-1·mm-1 at pigeonpea harvesting. Benefit was doubled at 50% of full irrigation and >4 times at 75% of full irrigation.