Integrating microdosing of fertilizers with biological control agents for maize production in the Eastern Cape, South Africa.
Maize is an important staple crop in South Africa, and is also used for animal feed. In the Eastern Cape Province in South Africa a larger percentage of the farmers are small scale farmers and lack financial resources to apply the recommended levels of fertilizer inputs for optimal production. The currently promoted system of maize production in the Eastern Cape was designed specifically for commercial production, e.g., it is based on the use of agrochemicals to control plant diseases and pests, combined with the use of synthetic fertilizers to provide nutrients, and the application of large quantities of lime to solve soil acidity issues. The currently available mechanical equipment used to fertilize maize are only for row fertilization, whereas in between rows there may be losses of fertilizer due to the distance to the roots. Small scale farmers of this region do not apply lime. Consequently, maize yields are very low for small scale farmers in the Eastern Cape Province, relative to commercial farmers. Both biotic and abiotic factors combine to reduce maize yields. These include root diseases caused by Rhizoctonia solani Kühn and other root pathogens and poor soils (highly acidic soils with low nutrient content, especially of P and Mo). Given that the farmers do not treat the seed, lime the soil, and apply little or no fertilization, yields are consistently low. One goal of this study was to control root rot on maize caused by R. solani using a biocontrol agent, and a potassium silicate fertilizer as a priming agent of plant disease resistance. A commercial biocontrol agent, Eco-T® (a.i. Trichoderma harzianum Strain kd), is known to control most pathogenic root fungi, including R. solani. This treatment was evaluated alone and in combination with potassium silicate (KSil) in field trials over two seasons. Two KSil formulations were tested, namely a liquid and a slow release formulation. All treatments significantly reduced damage by R. solani, with T. harzianum plus the liquid formulation of KSil resulting in the highest level of control in Season 1, and T. harzianum alone providing the highest level of disease control in Season 2 (p = 0.018). There was no significant difference in the levels of control provided by T. harzianum and KSil applications when they were applied individually. All treatments significantly increased the maize yield relative to inoculated control. The treatment that gave the highest percentage difference relative to the inoculated control was KSil liquid formulation combination with T. harzianum, the combinations gave a significant 45% increased yield over the inoculated control. This means that this combination is an option for the farmers. Small scale farmers in the Eastern Cape produce maize in poor soils that have low pH levels, very high levels of acid saturation and low nutrient levels, especially of P. The second part of this study was to investigate achievable approaches to liming and fertilization for small scale farmers in the Eastern Cape. These included fertilization and liming by micro-dosing of 2:3:2 (34) fertilizer, superphosphate fertilizer and dolomitic lime using a cap of a soda bottle to measure out approximately 5g to each maize plant, applied directly into the planting hole. In order to fix atmospheric nitrogen and to solubilize phosphates in these acidic soils, a nitrogen-fixing isolate of B. megaterium was drenched into the planting holes. Micro-dosing of 2:3:2 (34) fertilizer increased maize yields by 64.6% and 13.6%, over the two seasons of the study. Micro-dosing with superphosphate fertilizer also significantly increased the maize yield (P = 0.001) by 50.5% and 37.4%. The combination of B. megaterium and 2:3:2 (34) fertilizer significantly increased the maize yield (P = 0.001) by 54.7% and 48.1% in season 1 and 2, respectively. The combination of B. megaterium, 2:3:2 (34) fertilizer and lime significantly (P = 0.018) increased maize yield, maize plant height, and stem diameter in both seasons. The increases in both seasons were consistent as a result of this combination compared to the 2:3:2 (34) fertilizer and lime combination. Whenever B. megaterium was included in the treatment combination, yields were increased, although not significantly. It was therefore concluded that micro-dosing of fertilizers can have a significant role in improving the yields for small scale farmers that cannot afford to apply the recommended levels of fertilizer or lime. It was also concluded that the use of B. megaterium is beneficial when combined with NPK and P fertilizers. Field experiments over three seasons were designed to evaluate the integration of the treatments applied in the field experiments mentioned above. The study was conducted in a field with a pH of 4.0 and an acid saturation of 54%. The methods included micro-dosing and spot application of fertilizers and lime. A strain of B. megaterium was used as a nitrogen fixer and phosphate solubilizer. For maize root disease control, the methods employed included the use of a biological control agent, T. harzianum and potassium silicate as a plant defense activator. The aim of the study was to reduce input costs whilst still providing adequate fertilization and root disease management. R. solani significantly reduced maize yields, by up to 34%, but treatment of maize seed with T. harzianum, or B. megaterium reduced losses over the three seasons from 34% to 16% and to 10%, respectively. In Season 1, the integration of all treatments (T. harzianum, B. megaterium and potassium silicate) increased maize yields by 130% relative to the R. solani inoculated control. The plots with the highest yields in the presence of R. solani were treated with T. harzianum (216%), followed by T. harzianum plus potassium silicate (214%), and lastly plots treated with T. harzianum plus B. megaterium (178%). A similar trend was observed over the three seasons. A cost benefit analysis of the integrated management of maize grown under acidic conditions and also in the presence of R. solani was undertaken after the three seasons of field experiments. The first experiment evaluated the control of R. solani using the T. harzianum, priming of plant resistance using potassium silicate, as well as the combination of T. harzianum and potassium silicate. The second experiment evaluated micro-dosing of 2:3:2 (34) fertilizer and lime, and the use of B. megaterium as a nitrogen fixer and phosphate solubilizer. The third experiment evaluated the integration of micro-dosing of 2:3:2 (34) fertilizer, superphosphate, lime and B. megaterium. The current retail prices were used. It was observed that the combination of T. harzianum and the potassium silicate liquid formulation consistently gave the highest returns on investment in controlling R. solani over the three seasons. Full fertilization consistently provided a negative return, with a mean loss of R3, 363 over three seasons, relative to the Untreated Control, which was not fertilized. Micro-dosing with lime plus 2:3:2 fertilizer gave the highest net return on investment. This was significantly different (p = 0.001) to both the Untreated Control and the Full Fertilization in Season 1. However in Season 2, the combination of B. megaterium plus 2:3:2 (34) fertilizer micro-dosed resulted in the highest net return that differed significantly from both the Untreated Control and the Full Fertilization. In the integration experiment all treatments in Season 1 gave a significantly higher yields and increased net returns on investment, relative to the R. solani inoculated control, with the lowest giving a 39% net return and the highest giving a 65% net return. In Season 2 none of the treatments resulted in significantly higher yields. In Season 3 a repeat of Season 1 results was seen where all treatments resulted in a significantly higher yields and net returns relative to the R. solani inoculated control, with the exception of B. megaterium in the presence of the pathogen. Two treatments, namely T. harzianum only and T. harzianum plus B. megaterium were consistently among the top three treatments that significantly controlled R. solani. The combination that gave consistently higher return on investment in the control of R. solani and also in the provision of nutrients was the T. harzianum plus B. megaterium plus micro-dosed 2:3:2 (34) and lime. It was therefore concluded that a cost effective method of fertilization and liming that will suit the Eastern Cape small scale farmers is micro-dosing rather than conventional method. Moreover incorporating B. megaterium improved yield consistently at little cost. For the concurrent control of root pathogens such as R. solani, it is recommended that the small scale farmers use T. harzianum, and possibly potassium silicate.