No-tillage (NT) combined with soil surface cover is effective in reducing runoff, and soil and nutrient losses by water erosion, but this effectiveness also may be affected by sowing direction and slope length. The objective of this work was to explore the impact of previous crop residue, sowing direction, and slope length, under NT, on available phosphorus losses (extracted with the Mehlich-1 solution) from eroded sediments produced by simulated rainfall. The treatments included soil cover by residues of three crops (maize, wheat and soybean) at two rates (50% and 100% of the dry mass production) and two sowing directions (contour and up and down slope). A field experiment was carried out under simulated rainfall at a constant intensity of 65 mm h^-1. Slope length was reproduced by adding water flow to plots of standard length. Phosphorus concentrations in the sediments were significantly lower (P < 0.05) after maize than after soybean and decreased with increasing slope length for all the three crops used as soil cover. A limiting threshold of slope length has been identified, above which residue failure occurred, so that NT had no efficiency in controlling losses of phosphorus. Sowing cross to the slope and residue application at the highest rate increased the threshold of slope length above which sediments are produced by water erosion, and also decreased the rates of sediment and phosphorus losses. Phosphorus losses were significantly lower (P < 0.05) under maize and wheat residues than under soybean residues. Contour sowing combined with previous crop residues left on the soil surface, is not always efficient enough in dissipating the energy of runoff over long slope lengths, also reducing the success of soil cover in controlling phosphorus losses. Therefore, agricultural and environmental managements should take into account the risk of crop residue failure and the subsequent increase in soil and sedimentary phosphorus losses by erosion.

免耕（NT）与土壤表层覆盖可有效减少径流以及因水蚀而造成的土壤和养分流失，但播种方向和坡度也可能会影响这种效果。这项工作的目的是探讨在NT下先前作物残渣，播种方向和坡长对模拟降雨产生的侵蚀性沉积物中可利用的磷损失（用Mehlich-1溶液提取）的影响。处理方法包括三种作物（玉米，小麦和大豆）的残留物以两种比率（占干物质产量的50％和100％）和两个播种方向（等高线和上下坡度）覆盖土壤。在模拟降雨下以65 mm h ^-1的恒定强度进行了野外试验。通过在标准长度的样地上增加水流来再现边坡长度。玉米种植后的三种作物中，沉积物中的磷含量均显着低于大豆后（P <0.05），并且随着坡长的增加而下降。已经确定了边坡长度的极限阈值，在该阈值之上发生了残余物破坏，因此NT在控制磷的损失方面没有效率。播种以最快的速率越过斜坡和残留物，增加了斜坡长度的阈值，在该阈值以上，水蚀产生了沉积物，并且还降低了沉积物和磷的流失率。玉米和小麦残留下的磷损失显着低于大豆残留下（P <0.05）。等高线播种与以前残留在土壤表面的农作物残渣相结合，并不能总是足够有效地消散长坡度上的径流能量，也降低了土壤覆盖在控制磷素损失方面的成功率。因此，农业和环境管理应考虑到农作物残渣破坏的风险以及随后因侵蚀而增加的土壤和沉积磷损失。