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José Mansilla Martínez, José-Arturo de Juan Valero, Alfonso Domínguez Padilla and María-Raquel Picornell Buendía

Abstract

High yields with low costs require that sugar beets be kept free of weeds, during critical periods, using labor or chemical treatments. Since the critical periods for this crop in Castilla - La Mancha (Spain) are unknown, the first goal of this study was to determine the effect of early and late competition on yield. The second goal was to determine the critical periods, while taking into consideration the semiarid climatic conditions of this region. Two irrigation farms located in the province of Albacete are dedicated to sugar beet cultivation. These two farms were chosen to carry out the tests March (140,000-150,000 seeds ∙ ha-1) and harvested in October. Two simultaneous and complementary experiments were carried out in each year and farm. Two scenarios were considered with eight different treatments each. In the first one (With Weeds Until - WWU), plots were infested by weeds up to a certain date. In the second one (Free of Weeds Until - FWU), plots were kept free of weeds up to a certain date. For each test, a randomised experimental blocked field was designed and there were four repetitions, each of them containing eight elemental plots (12 m2). Each plot was weeded by hand or weeds were left to grow till a definite date.The results indicated that a 1% loss of yield was reached in the early competition after 14 days, while a loss of 5% was reached after a period of 41 days after it was infested. The results also indicated that in late competition, if a crop is kept clean for 124 days and it is infested afterwards, a 1% loss is reached. However, the loss increases to 5% if the plot is kept clean for 111 days. For a 1% loss the critical period is 110 days and 70 days for a 5% loss.

Open access

Bernard Baffour, Michele Haynes, Mark Western, Darren Pennay, Sebastian Misson and Arturo Martinez

Abstract

Until quite recently, telephone surveys have typically relied on landline telephone numbers. However, with the increasing popularity and affordability of mobile phones, there has been a surge in households that do not have landline connections. Additionally, there has been a decline in the response rates and population coverage of landline telephone surveys, creating a challenge to collecting representative social data. Dual-frame telephone surveys that use both landline and mobile phone sampling frames can overcome the incompleteness of landline-only telephone sampling. However, surveying mobile phone users introduces new complexities in sampling, nonresponse measurement and statistical weighting. This article examines these issues and illustrates the consequences of failing to include mobile-phone-only users in telephone surveys using data from Australia. Results show that there are significant differences in estimates of populations’ characteristics when using information solely from the landline or mobile telephone sample. These biases in the population estimates are significantly reduced when data from the mobile and landline samples are combined and appropriate dual-frame survey estimators are used. The optimal choice of a dual-frame estimation strategy depends on the availability of good-quality information that can account for the differential patterns of nonresponse by frame.