Determination of the effects of crop rotation, water harvesting and soill fertility management on Nitrogen and water use efficiency of wheat in Njoro Sub-County Kenya.

Abstract

Wheat production in Njoro Sub - County, Nakuru, Kenya is constrained by many problems including low soil moisture and nitrogen (N) levels resulting in low wheat yields. Thus, the experiments to determine the effects of water harvesting (WH), crop rotation (CR) and soil fertility management (SFM) on N use efficiency (NUE), water use efficiency (WUE) and performance of wheat were conducted at Kenya Agricultural and Livestock Research Organization (KALRO) in Njoro between 2014 and 2016. Three factors were evaluated in a randomized complete block design (RCBD) with split-split plot replicated three times. These factors included (i) two levels of WH (main plot) (flat bed and tie ridge) (ii) four levels of CR (sub-plot) with different crop sequence each year [(CR1 = wheat (Triticum aestivum - lablab (Lablab purpureus) - T aestivum); CR 2= T aestivum -green pea (Pisum sativum) - T aestivum); CR 3 =T aestivum -potato (Solanum tuberosum) - T aestivum); CR 4 = Continuous wheat for 3 years)] and (iii) six levels of SFM (sub-sub-plot) [FYM at 5 t ha"; green manure (Leucaena trichandra) at 2.5 t ha"; calcium ammonium nitrate (CAN) fertilizer at 25, 50 and 75 kg N ha"; and untreated control]. Data was subjected to analysis of variance (ANOVA) using Genstat and mean separation was performed using least significance difference (Lsd) at 5% level of significance. Results showed that NUE and NUpE was improved when (T aestivum) was preceded by either L.purpureus or P. sativum in the CR treatments. Soil fertility management (SFM) significantly (p < 0.05) influenced NUE, NUtE, NUpE as well as WUE as well as yield and biomass. Two - way (CR x SFM) interactions significantly (p < 0.05) affected NUE, NUtE, NUpE as well as WUE and yield of wheat. Green manure (GM) on plots previously occupied by a legume (L. purpureus) or P. sativum) increased NUE by 46% while NUpE of wheat was improved by 36% when wheat was grown with the lowest rate (25 kg N ha') of inorganic fertilizer on plots that were previously on green pea. The lowest rate ofN (25 kg N ha') after L. purpureus or P. sativum improved NUtE by 14 and 12%, respectively. However, a three - way (WH x CR x SFM) interaction showed significant (p < 0.001) effect on WUE and grain yield. Wheat planted with FYM at 5 tonnes ha' on flat beds (WHl) previously occupied by L. purpureus significantly (p < 0.05) increased WUE and grain yield 25% and 31 %, respectively. In order to maximize NUE and its attributes L. purpureus or P, sativum may be used as precursor crops to T aestivum in the CR systems. Organic fertilizer. (FYM or GM) positively influenced UE and its attributes, WUE and grain yield of wheat. This could replace inorganic sources ofN if a legume pre-crop to T aestivum.