Push-pull technology is very effective for integrated pest, weed and soil management in cereal- based farming system (Khan et al., 2014). Considering this, we conducted a two year experiment to investigate the effect of PPT on controlling stem borer and striga infestation, improving soil fertility and grain yield with maize crop. The result of this study showed that the push–pull plots effectively controls striga hermonthica, resulted in increase plant height and grain yield in all study districts except Gozamin district with no striga occurrence. Even though striga was not emerged in Gozamin district in the push-pull and maze monocrop plots but still growth and yield of maize were increased in the push-pull plots. This is because N fertilizer has played vital role in enhancing vegetative growth and resulted in increment on plant height and grain yield (Sakatu, 2017). Ullah et al., (2018) also reported that as nitrogen increase cells protein content increase and size of plant cell increases, as a result of that leaf area and photosynthesis rate rises which ultimately make the plant taller and higher grain yield.
Similarly desmodium is a legume crop and essential in enhancing soil fertility status through biological fixation of atmospheric nitrogen (N2) and increase organic matter, practically eliminating soil erosion (Giller, 2001). The result of this study were consistent with those result observed in on farm studies conducted in eastern Africa where the technology is equally effective in controlling striga with increased growth and maize yield ( Khan et al., 2008; Midega et al., 2015; Hailu et al., 2018; Khan et al., 2006; Asmare, 2014). These results corroborate earlier findings in western Kenya that reported effective control of striga through hindering striga seed germination by the released root exudates of desmodium ( Midega et al., 2010). Desmodium contain root exudates which hinders germination of striga seeds (Tsanuo et al., 2003; Hooper et al., 2009, 2010). This provides a novel means of reduction of striga seed bank in the soil. These contribute to the importance of intercropping with desmodium in smallholder cereal based farming systems in north western Ethiopia. The significant reductions in the number of emerged striga in the push–pull plots observed in the current study across the study sites over the cropping seasons indicates stability of the striga control efficiency of desmodium and suggests that its use in smallholder farming systems in striga prone areas has potential to stabilize these systems.
Similarly, the result of this study showed that the push–pull plots effectively controls stemborer, resulted in increase plant height and grain yield in all study districts than monocrop plots. In push-pull plots stemborer control through companion cropping is mediated by green leaf volatiles emitted by the companion crops (Khan et al., 2010). Previous studies have shown that Napier grasses are preferred to maize for oviposition, and with minimal feeding and survival of stemborer larvae on Napier grasses (Midega et al., 2011). As compared to monocrop plots in push-pull plots low survival rates of stemborer larvae on Napier grass is favorable for conservation of the parasitoids by providing continuous shelter to natural enemies and therefore improving biological control of stemborer. Additionally, use of green leaf desmodium has been shown to repel stemborer moths resulting in effective control of stemborer (Khan et al., 2006a). Moreover in push-pull plots volatile organic compounds emitted by desmodium, including (E)-ocimene and (E)-4,8-dimethyl-1,3,7-nonatriene repel stemborer moths (Khan et al., 1997, 2000) and attract stemborer natural enemies and reduce stemborer attack in maize crop (Midega et al., 2009, 2014b). In addition to controlling pests, the present study also identified that Push-pull technology also enhances soil fertility and grain yield. The greater crop yields and productivity of push-pull plots relative to maize monocrops result from complementary use of resources for growth by the intercrop components (Willey, 1979; Ofori and Stern, 1987; Rao and Singh, 1990; Willey, 1990). The push-pull technology practiced in the study sites increased grain yield and soil fertility through different ways. Desmodium is an essential legume crop in enhancing soil fertility status through biological fixation of atmospheric nitrogen (N2) and increased organic matter, eliminating soil erosion (Giller, 2001). Desmodium is effective legume crop which can fix over 300 kg N/ha per year (Whitney, 1966). Even though the study was conducted for only two years still in push-pull plots there were significant increment in soil fertility status, growth and yield of maize because desmodium were added 300 kg N/ha per year through biological fixation (Whitney, 1966). This legume crop also improves soil organic matter content, nitrogen and conserves soil moisture which resulted in an increase in soil microbial diversity and activity (Midega et al., 2005; Khan et al, 2006a; Khan et al., 2002; Midega et al., 2008,2009). The differences in soil fertility status between push-pull and maize monocrop plots may be attributable to N2 fixation of Desmodium in push-pull plots as compared to maize monocrop plots. Our study showed that the inclusion of legumes is essential for soil fertility sustenance as they contribute to soil fertility enhancement through biological fixation of atmospheric nitrogen (N2) in the push-pull than maize monocrop plots.
Similarly available P, K, organic matter, total nitrogen and organic carbon were increased in the push-pull plots than maize monocrop plots. The cause of increment in push-pull plots and decrement in maize monocrop plots was due to desmodium increase nitrogen content. This nitrogen increment in low fertile soils (acidic soils) can leads to a release of phosphorus, potassium, organic matter, total nitrogen and organic carbon reserves inside the soil. In accordance to our result as Kas et al. (2016) and Giller, (2001) indicated that the increment of nitrogen through biological fixation resulted in a significant increase of phosphorus, potassium, organic matter, total nitrogen and organic carbon. Similarly Cong et al. (2016) revealed that presence of nitrogen nutrient in the soil system increased phosphorus and potassium content. This may be due to positive interaction balance of phosphorus and potassium in the soil system under increased mineral nitrogen at push-pull plots than monocrop plots. Push-pull technology that involves maize intercropping with desmodium and improves and maintains soil health has an important role in integrated soil fertility management strategy and in turn leads to increased growth and grain yield of maize ( Altieri and Nicholls, 2003).