Growth and yield response of sorghum to omission of nutrients under contrasting landscape positions in the semi-arid tropical environment.

This study aimed to identify sorghum yield-limiting nutrients, targeting landscape positions. Nutrient omission field trials were conducted across 52 sites under distinct landscape positions during the 2020 and 2022 cropping seasons. The fertilizer treatments were All blended (containing N, P, K, S, Zn, and B), All compound with the same nutrients, All individual with the same nutrients, 150% of All blended, 50% of All blended, All blended-K, All blended-S, All blended-Zn, All blended-B, NP-only, and control (no fertilizer). These treatments were arranged in a randomized complete block design with two to three replications under each landscape position. Results revealed that the yield response to the application of different nutrient sources at different rates significantly decreased with increasing slope, and yield among landscape positions was in the order of hillslope < mid-slope< foot-slope. Increasing the all-blended treatment by 50% increased grain yield by 44% and 147% over the application of 50% of all blended nutrients and the control, respectively. Yield differences among all blended, compound, and individual nutrient applications were not statistically significant. The omission of K, S, Zn, and B had no significant effect on yield compared with the recommended NP-only. Soil carbon, nitrogen, and phosphorus are deficient in the study areas. The average soil moisture content ranged from 5.9% to 28.7% across landscape positions, with the highest at the foot slope. Grain K, S, Zn, and B concentrations increased from the upper to the lower slope positions. Further research is suggested to explore a meaningful interaction between different levels of yield-limiting nutrients and landscape positions.