Nutrient Management Strategies for Guangxi

Laibin and Fushui counties were selected as long-term monitored village sites in 2002. In past years, soil nutrient limitations were determined and verified, and soil nutrient variability maps were developed. In 2005, the study tested the influence of balanced fertilization (BF) on crop yields. In 2006, the researchers evaluated the effect of secondary and micronutrients on crop yields and continued to monitor changes of soil nutrient status over time.

At Fushui, magnesium (Mg), boron (B), and zinc (Zn) were applied every other year. Compared to the NPK treatment, citrus yield increased by 4,802 kg (8%) and income by US$677/ha with addition of B; by 3,826 kg (6.2%) and US$540/ha with addition of Zn; and by 2,757 kg (4%) and US$389/ha with addition of Mg. The balanced optimum (OPT) treatment receiving NPK plus all secondary and micronutrients produced the highest yield and income of 6,906 kg orange/ha and US$974/ha higher than the NPK treatment. After 5 years, soil pH remained at the same levels while organic matter content doubled as a result of continuous addition of high rates of organic manure. Available N, P, and K after harvest have kept fluctuating, inversely correlated with citrus yield, a reflection of the positive relationship between yield and soil nutrient removal by citrus.

Research in Laibin County examined the effect of omitting Mg and Zn in early rice, watermelon, and sugarcane. Early rice yield was increased by 250 kg/ha (5%) with application of 1.5 kg Zn/ha and by 175 kg/ha with application of 30 kg Mg/ha along with 207-76-225 kg N-P₂O₅^-K₂O/ha. Watermelon yield increased by 2,850 kg/ha (5%) with foliar spray containing 1.5 kg B/ha as borax and 1.5 kg Zn/ha as zinc sulfate along with 450-525-544 kg/ha. Compared to the treatment of 380-162-450 kg/ha, sugarcane yield increased by 3,375 kg/ha (3%) and 2,525 kg/ha (2%) with addition of 3.0 kg B/ha as borax and 2.25 kg Zn/ha as zinc sulfate, respectively. Guangxi-NMS-02