Some well-managed organic soils are known to have higher crop yield potential than conventionally managed soils due to the greater soil quality and the ability to tolerate weed competition. However, low available soil mineral N and P in some organic systems may mask such soil quality–related benefits. We hypothesize that when plant-available N and P are not limiting, tillage-based highly diverse organic crop rotations have less yield loss (better crop tolerance) due to weed competition and higher crop yields than no-till conventional systems with low-diversity rotations. A greenhouse study was carried out in Saskatoon, Canada, using long-term (18-yr) organically managed soils (ORG) and no-till conventional soils (CONV) with three crop rotation diversities (LOW, MEDIUM, and HIGH) to compare the crop tolerance to weed competition under standard soil nutrient management conditions and under excess supply of mineral N and P. Under fertilized conditions, crop biomass increased by 50% and 69% in ORG and CONV systems, respectively. Weed biomass was similar between ORG and CONV systems under nonfertilized conditions but was 14% greater in CONV when excessive N and P were supplied. Crop biomass loss (crop tolerance) was not different among cropping systems under excess fertilizer or under standard fertilizer levels. Even with greater weed biomass under fertilized conditions, the CONV system showed crop tolerance similar to that of the ORG system. Under nonfertilized conditions, the crop biomass yield was 43% lower in ORG compared with CONV, and even after mineral N and P were applied, ORG systems showed less (17%) crop biomass than CONV. Further, differences in crop tolerance were not identified among crop rotations under both fertilizer levels. Overall, this study revealed that there were no yield benefits or better crop tolerance to weed competition in organically managed soils compared with no-till conventional soils, even under nonlimiting soil macronutrient conditions.

中文翻译：

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非限制养分条件下有机和免耕常规土壤中的杂草竞争

众所周知，一些管理良好的有机土壤比传统管理的土壤具有更高的作物产量潜力，因为土壤质量更高，并且能够耐受杂草竞争。然而，某些有机系统中可用的土壤矿物质 N 和 P 含量低可能会掩盖这种与土壤质量相关的益处。我们假设当植物可利用的 N 和 P 不受限制时，基于耕作的高度多样化的有机作物轮作由于杂草竞争而导致的产量损失更少（作物耐受性更好），并且作物产量高于具有低多样性轮作的免耕传统系统. 在加拿大萨斯卡通进行了一项温室研究，使用具有三种轮作多样性（低、中、和 HIGH) 比较标准土壤养分管理条件和矿物质 N 和 P 供应过剩下作物对杂草竞争的耐受性。在施肥条件下，ORG 和 CONV 系统中的作物生物量分别增加了 50% 和 69%。在非施肥条件下，ORG 和 CONV 系统之间的杂草生物量相似，但当提供过多的 N 和 P 时，CONV 中的杂草生物量高出 14%。作物生物量损失（作物耐受性）在过量施肥或标准施肥水平下的种植系统之间没有差异。即使在施肥条件下杂草生物量更大，CONV 系统也显示出与 ORG 系统相似的作物耐受性。在非施肥条件下，ORG 的作物生物量产量比 CONV 低 43%，即使在施用矿物 N 和 P 后，ORG 系统显示出比 CONV 更少 (17%) 的作物生物量。此外，在两种施肥水平下，作物轮作之间没有发现作物耐受性的差异。总体而言，这项研究表明，与免耕传统土壤相比，有机管理土壤中没有产量效益或作物对杂草竞争的更好耐受性，即使在非限制性土壤常量营养素条件下也是如此。