Sandy soils in Terengganu and Kelantan support agriculture, but they are not stable nutrient repositories. A typical coastal sandy soil has CEC of 4–8 meq/100g; silica particles carry minimal charge, and sand-bound organic matter is scarce. Apply 200 kg/ha K fertiliser to such a soil, and within 4 weeks, 80% of it has leached past the rooting zone. The plant captures what it can during the first week; the rest is lost. The problem is not the fertiliser quality or the application timing; it is the soil's inability to hold cations. Raising CEC through humic acid and amino acid biostimulants converts a leaching environment into a retentive one, making every kilogram of fertiliser count.
轻质土壤中的淋溶损失
CEC is the sum of permanent negative charges on clay minerals, organic matter, and (in acid soils) aluminium oxides. Sandy soils are low in clay (<10% particles <2 µm) and low in organic matter (often <1.5% in coastal dune-derived soils). The result: total CEC of 4–8 meq/100g, compared to 15–25 in loamy soils. Applied K⁺, Mg²⁺, Ca²⁺, and trace cations are not attracted strongly to the soil matrix; they move with percolating water and escape the root zone within days of heavy rain.
Farmers compensate by applying more fertiliser more often. But this is economically unsustainable and environmentally problematic. The alternative is to raise the soil's charge density—its CEC—so that applied nutrients are held and available to the plant across the season.
腐植酸作为阳离子交换容量增强剂
Humic acids are large organic polymers with carboxyl (–COOH) and phenolic (–OH) functional groups. These groups carry negative charges at soil pH 5–8, creating the charge density that holds cations. SoilBoost EA (96.55% humic acid by TPS method, 12.21% S, pH 3.8) applied to sandy soils integrates into the top 10 cm, where it binds water and cations. The Eroy (2019) trial on seedling-stage soils showed that humic acid application raised exchangeable K from 400 to 714 me/100g—a 78.5% increase—in a potted medium with minimal clay content. The trial was conducted in a nursery setting, not a field, so the rate of integration and the long-term persistence differ from field-scale application. However, the direction of the effect is clear: humic acid builds K-holding capacity in low-clay systems.
氨基酸生物刺激剂作为辅助性CEC来源
Amino acids carry both carboxyl and amino functional groups, conferring CEC in their own right. Hyacinth Plus (amino acid biostimulant, CEC 21.39 meq/100g, proline 0.34%, glutamic acid 0.47%, glycine 0.54%) supplies additional charge capacity when mixed into the root zone. Unlike humic acids, which are larger and less mobile, amino acids penetrate the soil water film and may migrate laterally, extending the zone of elevated CEC beyond the mixing depth. Applied with humic acid, they create a composite system: humic acid provides bulk CEC and water-holding capacity; amino acids reinforce local charge gradients and supply cofactors for enzyme activity and osmotic regulation.
砂质土壤田间施用规程
初期积累阶段（第1年）：在作物种植前，SoilBoost 以10–15公斤/公顷的用量、Hyacinth Plus以15–20公斤/公顷的用量混入表层15厘米的土壤中。充分浇水。 维持阶段（第2年起）： 每年施用SoilBoost 5–8公斤/公顷和Hyacinth Plus 10公斤/公顷，具体施用时间视轮作安排而定，可在播种前或收获后进行。在降雨量大且易受淋溶影响的沿海土壤上，若产量响应趋于平稳，则每年维护用量可能需要增加SoilBoost 8–10公斤/公顷和Hyacinth Plus 12公斤/公顷。
双重效益：CEC与WHC
Humic acid raises not only CEC but also water-holding capacity (WHC). Sandy soils hold water only in the pore space immediately around grains; wilting point is reached quickly after rain stops. Eroy (2019) showed WHC rising from 80% to 88.7% in nursery soil supplied with humic acid. WHC is measured as the difference between field capacity (water held at 33 kPa matric potential) and wilting point (1500 kPa). In sandy soils, this range is compressed; humic acid increases the water retained at both field capacity and wilting point, extending the plant's access window. This is particularly valuable in years with delayed monsoon onset or early dry-season intensification.
监测CEC恢复情况
施用后第6个月和第12个月进行土壤检测，以追踪阳离子交换容量（CEC）的恢复情况。目标：在一年内将CEC从基线值4–8 meq/100g提高至10–12 meq/100g。 可交换钾（K）应按比例增加；若尽管CEC升高但钾仍持续淋失，需调查腐殖酸是否已渗透至整个根系区域，抑或仍分层滞留于表层。根系发育采样（12个月时开挖探坑）将揭示CEC的提升是否转化为更深、更广泛的根系。
Lal（2016）指出，沙质土壤中的土壤有机质积累速度慢于富含黏土的土壤，因为在通气良好的沙质基质中，有机质氧化速度更快。腐植酸是相对稳定的有机质形式，比新鲜堆肥更不易氧化，因此能更持久地提高阳离子交换容量（CEC）。 然而，由于现有的腐植酸会被土壤微生物逐渐矿化，因此必须每年重新施用以维持目标阳离子交换容量。
轻质土壤的成本效益分析
在轻质土壤上通过腐植酸提高阳离子交换容量（CEC）的经济效益显而易见。若在未经改良的沙质土壤（CEC 4–6 meq/100g）上一次性施用大量肥料，4周内会有70–80%的施用阳离子因淋溶而流失。若将同等量的肥料分3–4次少量施用，虽能将流失分散到多个生长周期，但会增加人工成本。 若将同等总量的肥料施用于添加了腐植酸的土壤（阳离子交换容量为10–12 meq/100g），则可保留60–70%的施用阳离子，既能支持植物吸收，又能降低总施肥需求。SoilBoost Hyacinth Plus的初期投入成本（在马来西亚约为800–1200美元/公顷）可通过减少肥料流失和提高养分利用效率，在1–2个生长季内收回。在降雨量大的地区（沙巴、沙捞越、东海岸），由于淋失压力极大，提高阳离子交换容量（CEC）已成为不可或缺的措施；这属于基础设施建设，而非额外投入。
与施肥时机的集成
在添加了腐植酸的沙质土壤中，每公斤施用的肥料效果更为显著。生长季节内一次性施用大量氮钾肥，其养分在土壤中的保留时间将比未改良的土壤更长，从而减少了分次施肥的必要性。 然而，在降雨量大的地区（如东海岸、沙巴、沙捞越）的极轻质土壤上，分次施肥仍属明智之举：在腐植酸混入土壤阶段施用目标钾肥量的60%，剩余40%于生长中期施用。此举可分散淋溶压力，并确保在两次施肥间隔期间，因淋溶损失而导致作物在养分需求高峰期出现养分短缺的情况。
参考文献
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