The effect of phosphorus fertilizer application rates on root biomass characteristics of irrigated sugarcane (saccharum officinarum. L.)

Abstract

A field experimental study was carried out at Mwenezana Estate in the southeast lowveld of Zimbabwe (25º10’S, 31º15’E, >400 m elev.). The objective of the study was to determine the effect of varying P fertilizer application rates on sugarcane root biomass characteristics. Study results show that upgrading P application rates to 100-200 kg ha–1 and 250 – 300 bands improved cane root numbers in the soil by 78.6% and 250% respectively in comparison with the 0- 77 kg P fertilizer ha–1 band root counts. Increasing P fertilizer application rates from zero to 300 kg ha–1 steadily diminished both lateral spread and vertical extension of cane roots. The no P fertilizer variants inflated their root volumes by 84.6% in excess of that recorded in the P300 treatments. Application of P200systematically increased root intensities by 726.5% in excess of those in the control treatments. However, increasing application rates to 250 – 300 kg P ha–1 reduced the root intensities over those in the control plots to 256%. These results clearly demonstrate that extensive lateral spread and depth penetration of sugarcane root system do not necessarily indicate elevated root biomass accumulations. The highest root efficiency was recorded in the P200 to P250 replicated plots and the least was in the control variants. Results clearly show that the 200 – 300 P fertilizer application rate band, which recorded the highest root count and root intensity while at the same time scoring the lowest root volumes and root extensions, had the most efficient root systems.