Effects of Fertilizer Application Depth on the Above- and Belowground Growth of Sugarcane Under Different Water Regimes and Machinery Performance

In Thailand, mechanical fertilization during sugarcane cultivation is performed by placing fertilizer at depths of 20 to 30 cm, although there is no specific evidence for the appropriate application depth. Thus, it was expected that root development would be affected by the availability of fertilizer, and sugarcane growth could be improved by introducing the optimum fertilizer depth. To confirm this hypothesis, a pot experiment was conducted by the applications of fertilizer at 10, 20, and 30 cm depths under both irrigated and drought conditions. Stalk weight, commercial cane sugar, and sugar yield at harvest tended to decrease in the well-watered groups and increase in the drought-stressed groups with increasing fertilizer application depths, but the difference was not significant within the same water regime groups. Underground sampling revealed that sugarcane roots were intensively distributed in the shallow layer, especially at depths of 0 to 20 cm; however, no significant differences in root density at any depth were found within the water regime. In addition, a field evaluation of the fertilizer applicator revealed that tractor slip rate and fuel consumption increased, while working capacity, speed, and efficiency decreased with increasing fertilizer application depth. Particularly large differences were observed between 20 and 30 cm depths, suggesting that fertilizer should not be placed deeper than 20 cm based on the efficiency of machinery performance. The results of the pot experiment suggested that the optimum fertilizer application depths should be 10 to 20 cm.