Effects of legume cover crops and sub-soiling on soil properties and maize growth in Machakos District, Kenya

Abstract

Incorporating legume cover crops into the cropping systems and sub soiling/ripping has been used as an alternative method of improving soil fertility, crop yields and minimizing soil erosion problems. The current study explored the use of legumes and subsoiling in Kalama division, Machakos District, Kenya. The area has an average annual rainfall of 600 mm which has 66% reliability. In order to achieve this objective, a survey and a field experiment were conducted to: identify the factors that influence the adoption of Conservation Agriculture (CA) technologies in Machakos District; determine the effect of legume cover crop, subsoiling/ripping on soil properties and maize growth. The survey was conducted in midseason of the long rains in the area (LR, 2008). This was in order to observe the land use trends, agronomic practices, farm resources and the soil fertility management practices practiced in the area. The target population consisted of the farmers who were instructed on or practiced conservation technologies introduced by the KARIlLRNP project in the district. The field experiments were carried out in a randomized complete block design in four farms during the 2008 long (LR) and short rain (SR) seasons. The first trial (LR, 2008) had three treatment groups (T 1=maize +dolichos + subsoiling, T2=maize + dolichos + no subsoiling, T3=maize alone + no subsoiling). The second trial (SR, 2008) had four treatment groups (T1= maize + dolichos + susbsoiling; T2 = maize + dolichos + no subsoiling; T3= maize alone + no subsoiling; T4 = maize with subsoiling). Socio-economic factors played a greater role in adoption of CA technologies with respect to gender, age, education and farmer's resources. Fifty seven percent of the respondents were female and more men were educated than female (65%). It was thus recommended that farmers be trained more on cover crops use as method of increasing soil fertility. Further there is a need to improve level of education with special focus on women in the area to enhance proper maximization of farms and improve food security. Results from the field experiments showed that rainfall amount and its distribution affected the growth of dolichos and maize. Early in the season, the dolichos had a higher ground cover than maize with a peak at 8 weeks after planting (WAP) and thereafter tended to decrease slowly due to moisture stress. A further increase in cover was noted at 14-16 \VAP after some rainfall showers 12 WAP. The maize did not recover from the drought spell and was harvested at 17 Wi\.P in SR, 2008. In LR, 2008, there was crop failure due to lack of adequate rainfalL There were significant differences in cover among the treatments at P :s 0.05 in all the different WAPs. In reference to legume biomass, there were no significant differences among the treatments at P :s 0.05 but T1 had greater biomass than T2. Different treatments showed differences in maize heights and subsoiled plots gave a higher height of 2-10 cm more than in the non-subsoiled plots as the VlAPs progressed. Plots with dolichos (Ti and T2) gave higher maize dry matter yield than the maize alone plots (T3 and T4) in LR, 2008. In SR, 2008, the maize dry matter yield was significantly different at P ~ 0.05 with higher yields in T3 and T4 than in TI and T2• This could also be due to lack of competition of nutrients, water and light with the legume cover crop. There was a significant increase in total soil nitrogen content in SR, 2008 compared to the initial characterization of the soils and this could be attributed to the dolichos in the field. The penetration resistance in all the plots ranged from 3.83- 4.18 kgcm' with T4 reporting the highest and T ilowest penetration resistance.