Irrigation levels affects biomass yields and morphometric characteristics of range grasses in arid rangelands of Kenya

BACKGROUND Production of range grasses under irrigation has been widely adopted in the arid environments of Kenya as a strategy for seasonal forage supply gap. However, their productivity has only been done under conventional methods without an evaluation of their performance at varied soil moisture conditions. This information is needed for making sustainable management of irrigation water and also increased pasture productivity at the current intensification of the production systems. METHODS Aboveground biomass of six rangeland grasses (Chloris roxburghiana, Eragrostis superba, Enteropogon macrostachyus, Cenchrus ciliaris, Chloris gayana, and Sorghum sudanense) in pure and mixed stands at 80, 50 and 30 % soil moisture field capacity (FC), and control under rainfed as main plots. The main plots were divided into 30 subplots and randomly allocated ten grass species in three replicates. The moisture content was monitored by gypsum blocks which aided in irrigation times and levels. Seeds were sown by broadcast method in tractor ploughed and harrowed to fine tilt land. Biomass and growth morphometric characteristics were measured at phenological growth stages of 10, 12 and 14 weeks, representing vegetative stage, flowering and seed setting and mature with ripened seed stages for the studied range grasses. RESULTS All the irrigated treatment yielded significantly (p ≤ 0.05) higher above ground dry matter than the rainfed. S. sudanense had the highest yields at 80 % FC (13.7 t ha-1), though not significantly different from the 50 and 30 % FC (11.6 and 7.7 t ha-1), respectively. C. gayana and C. roxbhurghiana yields were not significantly affected by changes in soil moisture content with yields ranging between 10.1 and 10.8 t ha-1. C. ciliaris performed better at 50 % FC (9.1 t ha-1). Differences in tiller numbers across the watering treatments and grass species were not significant, but very low under rainfed conditions. The tiller heights in all the species were lower under rainfed than irrigated treatments. S. sudanense had the highest tiller height and biomass followed by C. gayana and E. Macrostachyus, respectively. CONCLUSION Here we demonstrate that the production of range pastures under irrigation in the arid environments should consider individual species' responses to different soil moisture content for better yields and water conservation. The results show the species of importance for consideration under irrigation systems are S. sudanense and C. gayana.