查看更多>>摘要：? 2021 The AuthorsIntercropping has frequently been reported to provide good weed suppression. Here, we tested the hypothesis that the weed biomass in annual intercropping systems can be adequately forecasted based on the weed biomass obtained in pure stands of the component crop species. The aim of this analysis was to enlarge the understanding on the weed suppressive ability of intercrops, and specifically to shed light on the relevance of the mechanisms at the basis of weed suppression in intercrops and the factors governing this weed suppression. Based on a literature survey, a dataset covering 76 experiments, a total of 35 different crop species combinations and a total of 339 records was composed, with each record containing weed biomass of the intercrop as well as that of pure stands of the component species. Three models were evaluated and compared using the dataset. The first two models, the arithmetic mean (model 1) and the weighted arithmetic mean (model 2a and 2b) of the weed biomasses obtained in pure stand, resulted in a systematic overestimation of weed biomass in intercrops. This result confirms that the ability of intercrops to suppress weeds is in general well developed. A third model was constructed based on an extended version of the hyperbolic yield-density equation. Mathematical elaboration of this equation suggests the weed biomass in intercrops to be equal to the weighted harmonic mean of weed biomasses in pure stands (model 3), whereby weighting is based on the relative densities of the component species in intercrops. Comparison between observed and predicted data showed that the model accurately predicted weed biomass of simultaneous intercrops in mixed and row design. The harmonic mean indicates that weed biomass in intercrops is the outcome of the joint competitive effect of the component species, whereby the more strongly weed suppressive species contributes a more than proportional share. Such dominance of one of the species is generally referred to as selection. For intercrops with a less intimate entanglement of the two component species, either due to temporal (relay intercrops) or spatial (strip intercrops) separation, the harmonic mean tended to underestimate observed weed biomass. A contribution of complementarity, following from niche differentiation or facilitation between component species, to the weed suppression of intercrops is not accounted for in the harmonic mean model. The high accuracy of the predictions thus suggests that the density and the selection effect are the main mechanisms responsible for weed suppression in intercrops. Choice of component species, their mixing ratio and the total plant density of the intercrop were all shown to clearly influence the weed suppressive ability of the intercrop. With a prominent role of the selection effect, care should be taken that an overemphasis on weed suppressive ability in the design of intercropping systems should not result in the poorer weed suppressive species being outcompeted. Another important implication of the finding that weed biomass in intercrops can be accurately predicted based on weed biomass in pure stands of the component species is that variety selection for intercrops with improved weed suppression can simply be confined to variety selection in pure stands.
查看更多>>摘要：? 2021 Elsevier B.V.Increasing grain yield and protein content simultaneously in wheat (Triticum aestivum L.) is challenging. Efficient nitrogen (N) management strategies, such as mixed application of controlled-release urea and normal urea (CRUNU), has been considered as a potential method for overcoming this challenge. Here, we tested CRUNU application in the winter wheat variety, Xiaoyan22, during three growing seasons (2017–2020) to examine its effects on photosynthetic characteristics, grain filling, dry matter, and N accumulation and remobilization. We aimed to determine the effect of CRUNU application on wheat grain yield and protein content and its underlying mechanisms. The results from the three wheat-growing seasons showed that CRUNU application significantly increased grain yield and protein content at three N application levels, with an average increase of 3.89% in grain yield and 6.35% in protein content compared with the results obtained using normal urea (NU). The main determinant for the increased grain yield was the increase in apical grain weight, which was mainly due to the improvement in grain filling. At the three N application levels, increased N accumulation was observed in vegetative organs (pre-anthesis) following CRUNU application compared with NU application; however, CRUNU application did not improve the contribution rate of pre-anthesis N accumulation in grains. The increase in grain N accumulation and protein content were mainly attributed to elevated post-anthesis N accumulation and its improved contribution to grain N content. Because CRUNU application improved wheat grain yield and protein content without significant variations between the medium and high N application levels, we suggest that CRUNU application, in combination with optimum N application levels, can be considered an effective agronomic management strategy to improve grain yield and protein content in winter wheat.
查看更多>>摘要：? 2021 Elsevier B.V.The residue effects of tobacco (Nicotiana tabacum L.) nicotine on the subsequent maize (Zea mays L.) crop cultivated in soils differing in texture has rarely been studied for over a decade. The present study was conducted on sandy soil of Tabora, and loamy sand soils of Urambo, and Sikonge sites in Tabora region of Tanzania, to assess the residue effects of tobacco nicotine on latter performance of a maize crop. The experiment was laid out in a complete randomized block design with three replications. During the first cropping season (2017–18), the treatments were composed of one unfertilized cultivated plot of tobacco as a control and a fertilized cultivated plot, where the seedlings of flue-cured tobacco variety K326 were transplanted. Two separate plots were kept fallow for planting sole maize (DKC-8053) under fertilized and unfertilized conditions without any nicotine residue during the succeeding second (2018–19) and third (2019–20) cropping seasons. Moreover, in the first cropping season, in one fertilized tobacco plot, tobacco stalks after reaping leaves were incorporated in soil for natural decomposition, while in the other fertilized tobacco plot, tobacco stalks were uprooted. In the second and third cropping seasons, the residue nicotine was measured in soils and found to range from 0.25 to 0.86 mg kg?1 in both unfertilized and fertilized tobacco plots. The residue nicotine ranged from 0.92 to 1.05 mg kg?1 in fertilized tobacco cultivated soils with tobacco stalks. Results showed that nicotine residue in soil decreased maize grain yield by 0.08 t ha?1. The decrease of maize grain yield was also attributed to inadequate P and K levels in soils planted with tobacco. Therefore, this study recommends the supplemental application of the limiting P and K nutrients when planting maize after tobacco.
查看更多>>摘要：? 2022 Elsevier B.V.The authors regret that the x-labels forFig. 6b are not correct. The corrected Fig. 6 is below. There are no changes to texts in the paper. The authors would like to apologise for any inconvenience caused.
查看更多>>摘要：? 2021Seed distributors market lucerne to farmers based on the supposed winter activity of those cultivars. This study determines the amount of between-cultivar variation, in cultivars available to farmers, in annual dry matter production and seasonality of that dry matter production when grown in dryland grazing areas of south east Australia. Forty-seven cultivars of lucerne, that spanned the range of winter activity ratings, were defoliated every 6 weeks for a period of nearly four years at two contrasting dryland sites. At each site, annual and seasonal dry matter growth was measured over three yearly periods. The variation between cultivars was examined using models with random between-cultivar effects. At both sites and in most years, within the Australian commercial cultivars, the higher (97.5% quantile) annual growth cultivars had about 20–30% greater annual growth than the lower (2.5% quantile) annual growth cultivars. Whilst variation between cultivars in seasonality of growth was statistically detectable, the main feature was the small magnitude of this between cultivar variation. We suggest that dryland farmers in temperate regions (similar to south-east Australia) should make purchasing decisions of lucerne cultivar based on annual production, pest and disease resistance, persistence and grazing tolerance, and mostly ignore differences in seasonality of production.
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