Performance of Irrigation Scheduling on Nutrient Leaching in Sugarcane Under Sprinkler Irrigation System

ABSTRACT Fixed irrigation schedules in sugarcane often ignore dynamic crop‐water–soil interactions, leading to inefficiency and nutrient loss. This study assessed the Semi‐Solid Set Sprinkler Irrigation System (SSSSIS) at Mkulazi Sugar Estate during the establishment stage (first 3 months after planting; root depth of 0–30 cm). Sprinkler performance, soil moisture, salinity (Na + , Cl − ) and nutrient (N and P) dynamics were monitored under a fixed 14‐day schedule. CROPWAT 8.0 estimated crop water requirements at 28.7 mm per event, whereas the system applied 43.4 mm, a 51% excess, indicating significant water inefficiency. Although the distribution uniformity was high (87%), the application efficiency was suboptimal (71%). This surplus caused significant nitrogen leaching into the 30–60 cm depth (90.9 kg ha −1 ), representing a major fertilizer loss, whereas phosphorus leaching remained minimal (< 5.3 kg ha −1 ), consistent with its immobility in clay soil. Irrigation water salinity increased from 0.97 to 1.81 dS m −1 due to evapoconcentration in storage ponds, raising the root zone salinity to 2.7 dS m −1 , above the 1.7 dS m −1 sugarcane threshold, and posing a risk to crop health. If unmanaged, these risks may worsen as roots deepen. The study concludes that adaptive irrigation, initiated when soil moisture falls below crop‐specific thresholds, is necessary to meet crop demand, reduce nutrient loss and increase sustainability in clay–soil sugarcane systems.