Effect of Legumes on Nitrogen Use Efficiency of Wheat in a Short Term Crop Rotation in Njoro Sub-County

Aims: The study determined the effect of legumes in short term crop rotation (cereal – legumes cropping systems) on nitrogen use efficiency of wheat.

Study Design: A randomized complete block design (RCBD) was used in a 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: The treatments consisted of four pre-crops in the rotation systems (CR1 = Dolichos lablab (L. purpureus) as a pre-crop; CR2 = Green pea (Pisum sativum) as a pre-crop; potato (Solanum tuberosum) as a pre-crop; and CR4 = continuous wheat (Triticum aestivum), two water harvesting (WH) strategies (WH = flat beds; and WH= tied ridges) and six soil fertility management (SFM) strategies (SFM1 = untreated control; SFM2 = FYM at 5 t ha-1; SFM3 = Green manure (Leucaena trichandra) at 2.5 t ha-1; SFM4 = inorganic source at 25 kg N ha-1; SFM5 = inorganic source at 50 kg N ha-1; and SFM6 = Inorganic source at 75 kg N ha-1)..

Results: The results revealed that the value of NUE significantly (p < 0.001) increased when P. sativum and L. purpureus preceded wheat in the short term crop rotation system. The value of NUE increased by 39% and 44%, when wheat was preceded L. purpureus and P. sativum, respectively, relative to S. tuberosum. Under continuous wheat, NUE value was increased by 54.17% relative to potato as a pre-crop. Overall, the contribution of legumes (L. purpureus and P. sativum) as precursor crops was greater than those observed with potato and wheat as pre-crops.