Abstract

Sugarcane (Saccharum spp.) demands high amounts of potassium (K) for profitable yields, but high K application rates could challenge agronomic K efficiency due to leaching and salinity damage to young roots. This study hypothesized that a split dose rather than just a basal K application could represent a better strategy, especially in soils with low cation exchange capacity (CEC). The objective was to evaluate sugarcane performance as a function of ascending K application rates, and the crop’s response to split K application on soils varying in CEC and texture in Central-South Brazil.

Field trials were set up in three locations during 2016 to 2018: Chavantes, São Paulo (site 1, clay texture); Valetim Gentil, São Paulo (site 2, sandy-loam texture); and Ivinhema, Mato Grosso do Sul (site 3, sandy-loam texture). At each site, crop response was tested with potassium oxide (K₂O) rates ranging from 0-240 kg K₂O ha^–1. Additional treatments compared seven combinations of an intermediate K dose (120 kg K₂O ha^–1) split into basal (B) and a later top-dressing (TD) application 60-90 days after planting (0/120; 20/100; 40/80; 60/60; 80/40; 100/20; and 120/0, B/TD kg K₂O ha^–1, respectively). Tiller density, stalk yield and recoverable theoretical sugar content (RTSC) were determined in the plant cane and first ratoon cycles. Sugarcane stalk yields ranged from 93-125 Mg ha^–1, and from 80-130 Mg ha^–1, across all sites for plant-cane and ratoon cycles, respectively. Significant differences in sugarcane yields occurred between the three sites, and between crop cycles. Generally, crop response to K application dose was very weak, and significant only on the clay soil of site 1, indicating a more significant reliance on soil K reserves rather than on current K application. Split K dose affected sugarcane performance only at site 3 on sandy-loam soil, where yields significantly peaked under a B/TD combination of 40/80 kg K₂O ha^–1 and tended to decline towards the two extreme combinations (0/120, and 120/0). However, no response to splitting could be observed at the two other sites. The results of the present study highlight the need for precise determination of soil fertility in terms of texture, composition of the clay minerals, CEC, and total and available soil K status. Consequently, the design of K application management should be founded on crop requirements for target yields, and on the current need to maintain or replenish soil K status. Split K application appears a reasonable strategy on sandy soils; however, further research is required to determine the appropriate intensity of splitting during the crop cycle, taking into consideration the economic implications.

Keywords: Clay; leaching; Saccharum spp.; sandy-loam; split K application.