Foliar fertilizer is important for lettuce vegetable development and yield. The present investigation studied different types and ratios of bio-foliar fertilizer to water seaweed extract and water hyacinth (0:1, 1:10, 1:20 and 1:30) in comparison to different two commercially available foliar fertilizers on growth, and quality attributes of lettuce. Four pot and field experiments were undertaken in spring seasons of 2020 and 2021 in randomized complete block design using three replications. The findings revealed that lettuce yield and quality were dependent on the type and spraying ratio of bio-foliar fertilizer from seaweed and water hyacinth. Improved yield and quality of lettuce was found when bio-foliar fertilizers from seaweed and water hyacinth were sprayed at ratio 1:10 (increasing compared to control in 68–81% with seaweed; 61–70% with water hyacinth in pot experiment and 19% with seaweed; 14–17% with water hyacinth in field experiment). Nitrate content was within standard range <1000 mg kg-1 and brix content from 2.20-2.65% as compared to commercial foliar fertilizer. A close relationship was found between biomass yield (R2 = 0.46 to 0.66) and economic yield (R2 = 0.50 to 0.64) with type and ratio of bio-fertilizer. In conclusion, a bio-foliar fertilizer extracts from seaweed at a spraying ratio of 1:10 can be used to achieve better yield and quality for lettuce crop.

Most agricultural production in central Vietnam relies on sandy soils distributed along the sea coast. Because of their low exchangeable potassium (K) and low cation exchange capacity (CEC), careful adjustment of K fertilization on these soils is needed to minimize K leaching. Quantity/intensity curves were established on 24 sandy soils from Thua Thien Hue Province from which K buffering capacity (PBC) was calculated and compared with basic soil properties. Potassium buffering capacity was found to correlate best with soil texture and only a little with humus content, although these two characteristics are responsible for CEC. A simple equation based on sand content, which is easier to determine than clay content, is proposed to calculate optimum exchangeable K level as a function of target K level in soil solution.