Effects of conservation tillage on soil properties, moisture conservation and yield of Maize and Cowpea in semi-arid Eastern Kenya
Miriti, Joseph M
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Soil water conservation through tillage is widely accepted as one of the appropriate ways of addressing soil moisture constraints in rainfed agriculture. A field experiment was conducted for 6 seasons between 2007 and 2009 to evaluate the effects of tillage practices on soil physical properties, water conservation, yield of maize and cowpea, water productivity, fertilizer use efficiency and gross margins in Makueni County in eastern Kenya. Experimental treatments were a combination of three tillage practices and four cropping systems. Tillage practices were tied-ridges (TR), subsoiling and ripping (SR) and ox ploughing (OP). Cropping systems were maize sole crop (SM), cowpea sole crop (SC), maize-cowpea intercrop (MC) and maize sole crop + 5 Mg ha' manure (SMM). The treatments were arranged in split plots with tillage practices as the main plots and cropping systems as the sub-plots in. a Completely Randomized Block Design (CRBD). Each treatment was replicated 4 times. Soil profile moisture content was measured using the neutron probe gauge method and fertilizer use efficiency using 15N isotope labeled fertilizer. The results showed that tillage significantly (PsO.05) influenced soil bulk density, soil surface crust strength, surface roughness, saturated hydraulic conductivity (Ks) and infiltration rates between crop rows. SR significantly (PsO.05) improved the bulk density and total porosity of the hardpan which was at the 14-27 em soil layer. On average, OP had the lowest inter-row bulk density than in SR and TR. Inter-row basic infiltration rate in OP were twofold greater than in SR and TR tillage. Surface roughness in TR was twice more than that in OP and SR. Available water content (A WC) in the soil profile was consistently highest in TR and least in SR in all seasons. Ox-ploughing conserved more soil profile moisture than SR but significantly (PsO.05) lower than TR. Soil profile moisture was lowest in SC followed by MC and highest in SM and all cropping systems were significantly (PsO.05) different. Out of the 6 seasons, two recorded total crop failure due to drought. Highest 4-season average maize biomass, grain and yield components (plant height, harvest index, number of ears per m-2) were observed in TR ~hile they were similar in SR and OP. Manure application significantly increased (pSO.05) average maize grain yields by 33% compared to treatments without manure across the seasons. Intercropping significantly (PSO.05) reduced the 4-season mean grain yields by a third. Sole cowpea grain and biomass production under SR were less than in OP in all seasons implying SR was not suitable for cowpea production. In contrast with SC, SM yields were slightly higher in SR than in OP. Tillage differences in terms of crop water productivity and fertilizer nitrogen use efficiency were not significant. The percentage of nitrogen derived from fertilizer was more in maize than in cowpea. Tied ridging doubled land preparation cost while SR reduced it by a half when compared to OP. Net returns from maize production ranged from -16023 to +13293 KES ha-l and were positive in only two out of the four seasons. Although sowing maize with manure improved maize yields and net returns, this was restricted to the relatively wet seasons. Sole cowpea resulted in positive net incomes in OP tillage in all seasons. Compared with maize, sole cowpea production was more economically productive. Majority (78%) of farmers preferred growing maize to cowpea. Tied ridging was ranked the highest in terms of crop performance but OP was the most (44%) preferred by farmers. The major conclusion from this study is that subsoiling and ripping the soil along crop planting line without disturbing the soil between rows in the sandy loam soil had no significant moisture conservation and crop performance advantages over the OP tillage.