Wet Tropics region is ranked as the highest relative risk to Great Barrier Reef water quality with improved nitrogen management as priority. Sugarcane is a major crop in Wet Tropics and contributes 84 % of estimated anthropogenic dissolved inorganic nitrogen (DIN). Experiments were undertaken using a rainfall simulator (rate ≈ 90 mm h⁻¹, depth 48–67 mm) to measure solute amounts lost in runoff from raised beds planted with sugarcane on bare soil. Eighteen experimental plots, were constructed with a thin metal walls. Runoff was collected from 18 plots (1 m wide x 1.7 m long), plots were covered with shelters between simulations. Six plots had surface-applied fertiliser, six plots buried (subsurface) fertiliser in a band at 50–150 mm depth along the middle of plots, and a further six plots received no fertiliser. Fertiliser (Nitrophoska® Special) was applied at an equivalent rate of 46 kg-N ha⁻¹ (ammonium at 19 kg-N ha⁻¹ and nitrate at 27 kg-N ha⁻¹), 20 kg-P ha⁻¹ phosphate, 54 kg-K ha⁻¹ potassium and 31 kg-S ha⁻¹ sulfate.

Two plots from each fertiliser treatment rained upon 7, 20 and 55 days after fertiliser was applied (DAF). Two fertilised treatment plots were re-rained upon on 20 and 55 DAF and another two fertilised plots were re-rained upon a third time on 55 DAF.

No effect on runoff volume occurred when all treatments are included in analysis. On plots with repeated rainfall simulations, time to commencement of runoff decreased from rainfall simulation 1–2, no further decrease occurred.

Runoff nitrogen load was dominated by particulate nitrogen with: > 75 % for all fertiliser treatments and > 90 % for no fertiliser treatment. DIN concentration was dominated by nitrate and nitrite (NO_x-N) except for the first rainfall simulation on surface-applied fertiliser plots. Ammonia comprised more of the DIN in surface compared to subsurface treatment.

Evaporative concentration resulted in no difference in NO_x-N load between fertiliser treatments. Subsurface fertiliser placement did reduce ammonium concentration by 74 % and 90 % compared to surface applied fertiliser.

Phosphorus in runoff was dominated by particulate phosphorus being > 95 %. Subsurface application of fertiliser reduced phosphorus load in runoff from 0.9 to 0.14 kg ha⁻¹. Eighty-one% of applied surface sulfate was lost in runoff compared to 20 % of subsurface-applied fertiliser.

Results highlighted the importance of particulate nitrogen and phosphorus in runoff and suggested that evaporative concentration of nitrogen can occur at the surface between rainfall events.

湿热带地区被列为大堡礁水质的最高相对风险，其优先考虑的是对氮的管理得到改善。甘蔗是热带地区的主要农作物，占估计的人为溶解的无机氮（DIN）的84％。使用降雨模拟器进行实验（速率≈90 mm h ^-1（深度48-67毫米），以测量在裸露的土壤上种植甘蔗的高架床中径流中损失的溶质量。用薄金属墙建造了18个实验区。从18个样地（1 m宽x 1.7 m长）中收集了径流，模拟之间用掩体覆盖了样地。六个地块采用表面施肥，六个地块沿地块中部在50-150 mm深度的地带埋藏（地下）肥料，另外六个地块未施肥。以46 kg-N ha ^-1（铵在19 kg-N ha ^-1和硝酸盐在27 kg-N ha ^-1），20 kg-P ha ^-1磷酸盐的当量比例施用肥料（Nitrophoska®Special），54 kg-K ha ^-1钾和31 kg-S ha ^-1 硫酸盐。

施用肥料（DAF）后第7、20和55天，每种肥料处理的两个地块都下了雨。在20和55 DAF上重新灌溉了两个施肥处理田，在55 DAF上第三次重新灌溉了另外两个施肥田。

当所有处理都包括在分析中时，对径流量没有影响。在具有重复降雨模拟的样地上，到开始降雨的时间从降雨模拟1-2开始减少，没有进一步减少。

径流氮负荷主要是颗粒氮，其中：所有肥料处理> 75％，无肥料处理> 90％。DIN的浓度主要由硝酸盐和亚硝酸盐（NO _x -N）决定，除了在表面施肥区的首次降雨模拟。与地下处理相比，氨在表面上包含更多的DIN。

蒸发浓度导致肥料处理之间的NO _x -N负载无差异。与表面施肥相比，地下施肥确实将铵浓度降低了74％和90％。

径流中的磷以大于95％的颗粒磷占主导。地下施用肥料可将径流中的磷负荷从0.9降低至0.14 kg ha ^-1。相比于地下施肥的20％，流失了81％的表面硫酸盐。

结果强调了径流中颗粒状氮和磷的重要性，并暗示了降雨事件之间地表会发生氮的蒸发浓缩。