Crop Residue Management and Termite Prevelance Under Conservation Agriculture in Zimbabwe

Abstract

The challenge of maintaining a permanent soil cover using crop residues under conservation agriculture (CA) among smallholder farmers in Zimbabwe is mainly attributed to competing uses such as livestock grazing the residues. There is also a belief that the residues attract termites which damage crops leading to yield loss. This study therefore investigated the effectiveness of using repellents as a residue management option, for protecting crop residues from grazing livestock during the dry season as well as the effects of retained residues on termite prevalence in CA systems. To address these objectives, two broad experiments were conducted. The first experiment identified, screened and tested the effectiveness of repellents in protecting the grazing of crop residues by livestock during the dry season through on-station and on-farm trials. The identified repellents were screened at Domboshawa and further tested in Madziwa and Hereford smallholder communal areas. In the second experiment, effects of different crop residue application rates (0 to 6 t/ha under CA) on termite abundance, crop lodging (damage) due to termite attack and soil properties compared to a control of conventional mouldboard ploughing system (CMP), were tested on two sites namely Kadoma and Chikombedzi in 2008/9 and 2009/10 seasons. Maize residues were applied in Kadoma whilst sorghum residues were applied in Chikombedzi as a surface mulch. On-station trials at Domboshawa in 2009 showed that cowdung, goat droppings, tobacco and chilli were possible livestock repellents since >50% of initially treated residues were not consumed after up to 3 weeks of cattle grazing. The optimum concentrations of cow dung (3 t/ha), goat droppings (0.5 t/ha), chilli (0.4 t/ha), tobacco scrap (1.2 t/ha) and soaked tobacco (0.3 t/ha), were established at Domboshawa. When these repellents were later tested on-farm in Hereford and Madziwa communally grazed fields in 2010, it became apparent that at Hereford, where there was alternative livestock feed, after 5 weeks, cowdung, soaked tobacco and tobacco scrap treatments, retained significantly higher residue amounts of 66.4%, 64.5% and 60.7%, respectively compared to the untreated control with 49.7%. On the contrary, at Madziwa, where there was no alternative feed, all residues were consumed within three days, irrespective of treatment. In the second experiment, the study showed that mulching fields with maize residues at application rates at 4 and 6 t/ha and sorghum residues at 6 t/ha under CA, increases termite numbers compared to CMP and CA with no mulching. On both sites, results showed no significant difference (p>0.05) in crop lodging as residue application rates increased within CA systems. However, significant differences in lodging between CA (42-48%) and CMP (30-34%) were observed in Kadoma from both seasons. In Chikombedzi, only 8.4% of crop lodging was observed under CMP compared to between 13 and 25% under CA in the second season. With respect to soil properties, no significant relationship was observed between increasing crop residue amounts and soil organic carbon (SOC) and aggregate stability (measured as mean weight diameter (MWD) and Middleton’s dispersion ratio (MDR) in Kadoma over the two seasons (p>0.05). However, in Chikombedzi, results showed that an increase in sorghum residue amount, resulted in a significant linear increase (p<0.05) in SOC ranging from 9.8 to 11.0 mg-C g -1 within two seasons of implementation. With respect to crop yields, results from Kadoma (2008/9), revealed significantly higher yields under CA ranging from 2 900 - 3 348 kg/ha compared to CMP with 2 117 kg/ha. However, there was no pattern observed on yield as residues increased under CA. In Chikombedzi, during the first season, residue effects were inconsistent across farmers though CA increased crop yield compared to CMP depending on other factors such as weeding and annual rainfall. The study thus demonstrated that crop residues can be protected from grazing livestock using repellents in Hereford with high biomass production that offers alternative feed for livestock but, ineffective in Madziwa with acute shortage of alternative winter feed. The study also demonstrated that increasing crop residue application rates under CA increases termite prevalence in Kadoma and Chikombedzi. However, there was no observed effect of increasing residue application rate on crop lodging but, a shift from CMP to CA increases lodging due to termites, leading to severe crop damage on maize crops, although much lower damage is observed on sorghum crops.