Assessing the interactions between tephrosia Biomass and inorganic fertilizers on soil Chemical properties and maize yield in Malawi
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Maize production in Malawi is commonly limited by low soil nitrogen (N) and phosphorus (P). Improved fallows of N-fixing legumes such as Tephrosia and Sesbania have been suggested as options for improving soil fertility in N-limited soils. The interactions of Tephrosia fallow biomass and inorganic fertilizers on soil chemical properties and maize yields were evaluated on two sites at Chitedze Agricultural Research Station in Malawi. The experiment was a factorial combination of3 levels of inorganic N (0, 45 and 68kg N ha') and P (0, 20 and 30kg P ha') plus a no input control. The treatments were laid out in a randomised complete block design (RCBD) with three replicates. The interaction effect of Tephrosia vogelii and Tephrosia candida fallow biomass incorporated into the soil and inorganic fertilizers on yield response was assessed and compared with yield obtained from the no input control. The rates of decomposition and Nand P release patterns from Tephrosia leaves, twigs, mixture of leaves and twigs and maize stover were r: 1: also evaluated using 20 em x 20 ern litterbags with 2 mm mesh size. The decomposition rates were in the following order: TC Leaves + twigs + stover>TV Leaves + twigs + stover>TC leaves + twigs=TV leaves> TC leaves = TV leaves + twigs >TC leaves .+ stovers=TV leaves + stoves>TV twigs>TC twigs>maize stover. Th~ N release rates were in the order ofTC twigs>TV twigs>maize stover>TC leaves and stovers>TC leaves + twigs>TC Leaves + twigs + stover>TV Leaves + twigs + stover>TV leaves>TC leaves>TV leaves + stover>TV leaves + twigs. P release rates were in the order of TC twigs>TC leaves + twigs=TC leaves>TC leaves + stovers>TC Leaves + twigs + stover>TV twigs>TV leaves + stovers-Tv leaves>TV leaves + twigs=maize stover=TV Lea.v. es +.twigs + stover. The level of organic matter and pH increased in all the treatments while it decreased under the control-treatment, Total N remained almost * . unchanged in all the plots after cropping. Available P decreased in all T. vogelii plots while it IV increased in T. candida plots where inorganic P was applied. Exchangeable K, Ca and Mg increased in all the plots irrespective of the type of amendment. The interaction of Nand P fertilizers with T. vogelii biomass significantly affected the grain yield. The treatment that received 45kg Nhaland 20kg P ha' produced significantly higher grain yields (6.8 t ha') tban all the other treatments except the treatment that received 68kg N ha-1 and 30kg P ba-1 (6.5 t ba-l). Compared to the no input control, combining 45kg N haiand 20kg P halor 68kg N ha' and 30kg P ha-I increased grain yield by 353% and 333%. On the other hand, these two rates increased maize grain yield by 24% and 18% over fallow treatment respectively. The results for T. candida showed that application of fallow biomass alone or in combination with Nand P fertilizers did not significantly affect grain yield. However, incorporation of T. candida biomass alone can raise maize grain yield by 193% over the no input control and between 153 and 220% . when inorganic fertilizers were used. ~H:.i4g'1h/er maize yields where T. vogelii and T. candida f ..• biomass alone were applied was partly due to higher nutrient (N)3.5%) concentration of their biomass and hence this point to the potential of these two species' biomass to provide N equivalents sufficient to support maize yields comparable to those produced by the inorganic fertilizers. Based on these results we concfude that high quality r~~idues such as T. candida and T. vogelii can be used as sources of nutrients to improve crop yields and soil fertility in N-Iimited soils. However, inorganic P fertilizer amendment is needed to correct the low soil available P levels to meet crop requirements.