Nutrient Management Strategies for Guangxi

Laibin County and Fushui County 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 2006/07, the authors evaluated the effect of secondary and micro-nutrients on crop yields and continued to monitor changes of soil nutrient status over time. Since zinc (Zn) was usually applied every second year, the effect of sulfur (S) on rice was examined in 2007.

For citrus grown at Fushui, the residual effects of magnesium (Mg), boron (B), and zinc (Zn) applied in the previous year were evaluated. The optimal treatment (OPT) receiving NPK plus all secondary and micronutrients mentioned above produced the highest orange yield of 98.8 t/ha and net income of US$27,380/ha.

Compared to the OPT, citrus yield and income decreased by 3.5 t (4%) and US$984/ha with Mg omission, by 7.7 t (8%) and US$2,137/ha with S omission, by 2.6 t (3%) and US$736/ha with B omission, by 7.8 t/ha (8%) and US$2,158 with Zn omission. Research in Laibin County examined the effect of omitting Mg and S in early rice and late rice. Early rice yield was increased by 147 kg/ha (+2.4%) with application of 60 kg MgO/ha and by 197 kg/ha with application of 30 kg S/ha along with 180-75-180 kg N-P₂O₅-K₂O/ha. Late rice yield showed marginal increases of 64 kg/ha (+1%) with residual Mg and 36 kg/ha (1%) with residual S along with 158-75-180 kg/ha. The data further suggest that the effect of Mg on rice yield is diminished over time and residual effects of both Mg and S from the early rice are minor. Thus, Mg fertilizer can be applied to rice every second year or perhaps even at a even longer interval.

After 6 years of continuously applying high rates of organic manure, soil pH and organic matter content remained stable across the citrus field. Available soil N, P, K have fluctuated and remain inversely correlated with citrus yield. Thus, higher yields result in lower available soil nutrient contents measured after harvest. In the paddy field, soil pH, organic matter content, and available K remained stable, while available soil N and P have declined. In the upland field, soil pH and extractable calcium (Ca) have increased due to application of agricultural lime. Available soil N and K have decreased, while available P has increased over time. Guangxi-NMS02