Influence of Crop Rotation and Soil Fertility Management Strategies on Water Use Efficiency of Wheat in a Changing Climate in Njoro Sub-County in Kenya

Aims: The study determined the effect of soil fertility management (inorganic and organic N sources) and short term crop rotation (cereal – legumes cropping systems) on water use efficiency of wheat in high potential areas. Study Design: A randomized complete block design was used with split-split-plot arrangement replicated three times. Three factors evaluated included water harvesting (WH), crop rotation (CR) and soil fertility management (SFM). The data obtained were subjected to an analysis of variance (ANOVA) using Genstat statistical package while the mean separation was performed using least significance differences (P =.05). Place and Duration of Study: The trial was conducted at the Kenya Agricultural and Livestock Research Organization (KALRO) fields based in Njoro for three years between 2014 and 2016 during rainy seasons. Methodology: Water harvesting was evaluated at consisted of flat beds (WH1) and tied ridges (WH2), crop rotation was tested at four levels comprising of Wheat- Dolichos lablab (Lablab purpureum)-Wheat- L. purpureum (CR1); Wheat-Greenpea (P. sativum) –Wheat (Triticum aestivum L)- P. sativum (CR2); T. aestivum L-potato- P. sativum –Potato (Solanum tuberosum) (CR3); and Wheat-Wheat-Wheat-Wheat) (CR4). Six different soil fertility management (SFM) strategies evaluated included SFM1 = untreated control; SFM2 = Farm Yard Manure at 5 t ha-1; SFM3 = Green manure (L.eucaena triachandra) at 2.5 mt ha-1; SFM4 = Calcium Ammonium Nitrate (CAN) at 25 kg N ha-1; SFM5 = Calcuim Ammonium Nitrate at 50 kg N ha-1; and SFM6 = Ammonium Nitrate (CAN) at 75 kg N ha-1. The Water harvesting (WH) and SFM were fixed on the same plot at the form and rate for the entire period of the study while crops were rotated between seasons. Water use efficiency was derived as a ratio of water use and grain yield and biomass. Results: Results revealed significant (P =.05) effect of crop rotation and soil fertility management on water use efficiency. However, water harvesting did not influence. While interaction of CR and SFM significantly (P =.05) influenced WUE and grain yield. Significant influence was also observed on WUE due to an interaction between WH and SFM. Dolichos lablab (L. purpureum) and green pea as pre-crops resulted in higher yield than when potato was the pre-crop and continuous wheat.  Use of inorganic N fertilizer with L. purpureum as a pre-crop resulted in higher grain yield than all other soil fertility management strategies evaluated. In conclusion, the use of green pea as a pre-crop during the short rain followed by wheat in long rains is a beneficial crop rotation systems and a climate smart strategy. In addition, organic N sources should be recommended for sustainable wheat production because it will positively influence the accumulation and slow release of soil moisture for increased water use efficiency.