SOIL PROPERTIES AND NUTRIENT UPTAKE OF MAIZE (Zea mays L.) AS INFLUENCED BY INTEGRATED NUTRIENT MANAGEMENT ON VERTISOLS OF HARAMAYA DISTRICT, EASTERN ETHIOPIA

Abstract

The declining state of soil fertility and productivity in Ethiopia can be attributed to the inadequate attention given to the biological, chemical, and physical properties of soil. Additionally, the high phosphorus fixing characteristics of Vertisols have posed a significant challenge to agriculture in the country, leading to phosphorus deficiency, and rendering inorganic fertilizers less effective. Greenhouse and field experiments were conducted at Haramaya University, eastern Ethiopia, to investigate the effect of mixed manure rates (0, 5, 10, and 15 t ha-1 ), blended nitrogen, phosphorus, sulfur, and boron (NPSB) fertilizer rates (0, 50, 100, and 150 kg ha-1 ), and cropping systems (maize monocropping and maize faba bean intercropping) when used alone or in combination on selected soil chemical properties, phosphorus adsorption and desorption characteristics, and performance and nutrient uptake of maize (Zea mays L.) in Vertisols. Five experiments were conducted. Relevant soil and crop data were collected from all the experiments and subjected to statistical analysis. The results of the first experiment revealed that the application of mixed manure significantly decreased the soil pH, calcium carbonate content, the amount and efficiency of adsorbed phosphorus, and the Freundlich adsorption coefficient and constant while increasing available P and percentage of desorbed P. The highest changes in these parameters were observed in the treatment that received 15 t ha–1 of mixed manure. The findings of the second and third experiments demonstrated a significant reduction in soil pH, phosphorus adsorption efficiency, Freundlich adsorption coefficient and constant (p ≤ 0.001), and also an increase in organic carbon, total nitrogen, and available phosphorus. Moreover, significant improvements were observed in the growth parameters of maize plants, including height and diameter, tissue nitrogen and phosphorus content and uptake, and total above-ground biomass. The highest improvement in the majority of these parameters was observed for the combined use of 15 t ha–1 of mixed manure and 100 kg ha–1 of blended NPSB fertilizer compared to the control as well as their sole application. The findings of the fourth experiment also showed that the quantities of adsorbed phosphorus in all treatments revealed an increasing trend with an increased rate of added P concentration from 100 to 500 mg kg−1 . However, the efficiency of adsorbed P decreased significantly as added P concentration rates increased from 100 to 400 mg kg−1 in all the treatments, and then decreased as the added phosphorus concentration advanced to 500 mg kg−1. Moreover, all treatments that received mixed manure and blended NPSB combined applications showed a significant increase in both quantity and percentage of desorbed P compared to the control. The Freundlich adsorption coefficient and constant were also significantly reduced because of the combined application of mixed manure and blended NPSB. Overall, the soil treated with a combined application of 15 t ha−1 of MM with 100 kg ha−1 of blended NPSB showed the highest reduction in both quantity and efficiency of adsorbed phosphorus, as well as Freundlich adsorption coefficient and constant while increasing the quantity and percentage of desorbed P. The findings of the fifth experiment indicated that intercropping maize with faba bean led xxii to a noteworthy reduction in soil pH, but significantly increased soil organic carbon. Similarly, the interaction of the cropping system and blended NPSB also revealed the highest value of soil total nitrogen in maize-faba bean intercropping with 150 kg ha−1 NPSB suggesting its ability to augment belowground biomass. However, available phosphorus was higher in maize monocropping with 150 kg ha−1 NPSB. The cropping system and blended NPSB were found to have a significant influence on maize plant height, diameter, above ground biomass, total nitrogen, and phosphorus uptake. The interaction effects of the cropping system and blended NPSB revealed higher total nitrogen and phosphorus uptake of maize including nitrogen content in monocropped maize with 150 kg ha−1 NPSB. In conclusion, intercropping maize and faba bean, along with blended NPSB fertilizer, could be a promising approach to improving soil fertility. However, for enhanced crop productivity, maize growth parameters and nutrient uptake require further investigation, particularly in reducing competition for light, water, and other nutrients. Therefore, it is recommended that further research be conducted to evaluate the long-term effects of combined application of mixed manure, blended NPSB, and cropping system on soil fertility and nutrient uptake of different maize varieties.