Changes in the properties of Fijian Oxisols over 30 years of sugarcane cultivation

Abstract

Sugarcane production plateaued in Fiji at ~4 million tonnes annually (average ~55 t/ha) during the latter part of the 1980s but, in recent years, despite the continuing release of high yielding varieties, the total production has decreased to under 3 million tonnes (average ~45 t/ha). This study was initiated to study the changes in the properties of Oxisols following sugarcane cultivation to ascertain whether yield declines were due to degradation of soil biophysical and chemical properties. The study lasted from 1978 (when the soils were first cleared for agriculture) to 2009. Soil (0–15, 30–40 and 70–80 cm) properties including pH, organic carbon, cation exchange capacity, water retention, bulk density, phosphate retention and exchangeable bases were monitored. The observed topsoil changes could generally be related to changes in organic matter and associated ion exchange properties. The major changes occurred in the first three years after clearing, but some changes continued for many years. Subsoil samples (30–40 cm) showed an increase in organic carbon after cane cultivation, probably due to soil mixing during land preparation, organic matter movement during cropping and decay of sugarcane roots. At 70–80 cm, small but significant increases in organic carbon were observed along with small decreases in pH. Overall, these changes indicate that careful management of topsoils is essential for maintaining soil fertility and hence sugarcane productivity on these highly weathered soils.

Phosphorus requirements of some selected soil types in the Fiji sugarcane belt

“…Generally, Oxisols have reasonable organic carbon contents (3-5%, Soil Survey Staff, 1999), but the two Oxisols analysed in this study have relatively low levels of organic carbon (1.8-2.4%) which is consistent with other work on sugarcane Oxisols in Fiji (Morrison et al, 2005). The notable decline in organic carbon in the sugarcane cultivated land could be due to the farming practices and tillage, which also has been reported by Morrison et al (2005). Organic matter is a significant source of major nutrients for plant uptake (Spain et al, 1983) and the organic carbon of the soils can be improved; however, this depends on the management practices during sugarcane farming such as retaining trash.…”

“…In this study, Ultisols have the highest organic carbon compared to the other soil types which is expected as Ultisols are often soils with substantial organic carbon. Generally, Oxisols have reasonable organic carbon contents (3-5%, Soil Survey Staff, 1999), but the two Oxisols analysed in this study have relatively low levels of organic carbon (1.8-2.4%) which is consistent with other work on sugarcane Oxisols in Fiji (Morrison et al, 2005). The notable decline in organic carbon in the sugarcane cultivated land could be due to the farming practices and tillage, which also has been reported by Morrison et al (2005).…”

“…FSC, 2012). It is obvious that sugarcane production at Vanua Levu had the highest annual phosphorus fertilizer usage in kg ha -1 due to low phosphorus levels found in the soils (Morrison et al, 2005).…”

“…Previous studies on phosphate adsorption on Fiji soils have shown that significant quantities of added P are strongly adsorbed by soils, especially by the Al and Fe oxyhydroxide materials, and only limited quantities (10-30%) of fertilizer P are utilized by plants (Chee et al, 1978;Morrison, 1978;Dandy and Morrison, 1980;Morrison et al, 2005). Although Singh (1982) made some preliminary studies, there has not been, however, any detailed study of the conditions under which fixed P becomes available over time to plants.…”

Talāsiga Lands in Fiji: Their Potential Expansion through Modern Farming Activities

“…The methods used in this study have been reported in Morrison and Masilaca (1988) and Morrison and Gawander (2016) and so only a summary is provided here. Three adjacent fields located on rolling terrain were studied; the soils at each site were from the same series and all were under forest cover in the late 1970 s (Table 1) when the study began.…”