North African knapweed (Centaurea diluta Aiton) is an annual weed that is widespread in southern Spain and is of increasing concern in dryland cropping systems. Despite its expanding range in Spain, there is limited information on the emergence timing and pattern of this species, knowledge of which is critical for developing more timely and effective management strategies. Therefore, there is a need to develop simple and reliable models to predict the timing and emergence of this annual weed under dryland conditions. A multi-location field experiment was established across Spain in 2016 to 2017 to assess the emergence of C. diluta. At each of 11 locations, seeds were sown in the fall, and emergence was recorded. Overall emergence averaged 39% in the first year across all sites and 11% in the second year. In both years, the main emergence flush occurred at the beginning of the growing season. A three-parameter Weibull function best described seedling emergence of C. diluta. Emergence models were developed based on thermal time (TT) and hydrothermal time (HTT) and showed high predictability, as evidenced by root mean-square error prediction values of 10.8 and 10.7, respectively. Three cardinal points were established for TT and HHT at 0.5, 10, and 35 C for base, optimal, and ceiling temperatures, respectively, while base water potential was estimated at −0.5 MPa.

中文翻译：

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模拟北非矢车菊（Centaurea diluta）的出现，这是一种在西班牙越来越麻烦的杂草

北非矢车菊（矢车菊Aiton) 是一种一年生杂草，在西班牙南部广泛分布，在旱地种植系统中越来越受到关注。尽管其在西班牙的范围不断扩大，但关于该物种出现时间和模式的信息有限，了解这些信息对于制定更及时和有效的管理策略至关重要。因此，需要开发简单可靠的模型来预测这种一年生杂草在旱地条件下的时间和出现时间。2016 年至 2017 年在西班牙各地建立了一项多地点实地实验，以评估C.稀释. 在 11 个地点中的每一个，都在秋季播种，并记录出苗情况。第一年所有站点的总体出现率平均为 39%，第二年为 11%。在这两年中，主要的出苗潮都发生在生长季节的开始。一个三参数 Weibull 函数最好地描述了幼苗的出苗C.稀释. 出现模型是基于热时间 (TT) 和水热时间 (HTT) 开发的，并显示出很高的可预测性，分别为 10.8 和 10.7 的均方根误差预测值。TT 和 HHT 的三个基点分别为 0.5、10 和 35 C 的基础温度、最佳温度和最高温度，而基础水势估计为 -0.5 MPa。