Weed community responses to soil type during transition to no-till practice on smallholder farms in Zimbabwe

Understanding drivers of weed density and diversity is essential for the development of weed management strategies. Here, we compared temporal changes in weed density and diversity under no-till (NT) and conventional (CONV) tillage systems in cotton–maize rotations on loam, clay loam and sandy loam soils immediately after transition to NT in Kadoma, Zimbabwe. The effect of tillage system on weed density varied through the growth season and was dependent upon soil type and species composition of the weed community. Although weed responses to tillage system varied amongst species, we identified general trend effects on weed density on specific soils. At 3 weeks after crop emergence (WACE), weed density on loam soils was 76% and 96% higher in NT than in CONV during the 2009/2010 and 2010/2011 seasons, respectively, and on clay loam soils it was 37% and 33% higher in NT than CONV, respectively. Weed densities in NT and CONV were similar across all soil types at 6 WACE during the 2009/2010 and 2010/2011 seasons and at 9 WACE in 2009/2010. Tillage system did not affect weed density during the growth season on sandy loam soils. Weed diversity (Shannon index) was at least 75% higher in NT than CONV on loam and clay loam soils at 3 WACE during both seasons. It is likely these increases in weed densities following conversion to NT will exacerbate already prevalent weed management problems in the smallholder sector. Earlier weeding is recommended to suppress weed emergence and reduce likely associated crop yield losses.     

Characterization of Acidovorax citrulli strains isolated from solanaceous plants

Acidovorax citrulli is the causal agent of bacterial fruit blotch disease of cucurbits. Strains of this pathogen are distributed into two major groups: Group I strains have been mainly isolated from melon and other non-watermelon cucurbits, while Group II strains have been mainly recovered from watermelon. Here we report the characterization of strains T1 and EP isolated from diseased tomato and eggplant plants, respectively, and further confirmed to belong to A. citrulli species. Based on PCR, PFGE, and rep-PCR, these strains showed high similarity to the Group II strain 7a1. Sequencing and comparative analyses revealed that the genomes of T1 and EP aligned with that of the Group II model strain AAC00-1, over 97.88% and 99.22%, respectively. The virulence of T1, EP, and 7a1 determined on tomato, eggplant, and watermelon was similar and significantly higher than that of Group I strain M6. In contrast, M6 was more virulent on melon. Expression levels of seven virulence genes measured 24 hr after inoculation of tomato, eggplant, watermelon, and melon showed that the expression pattern was generally similar in strains 7a1, T1, and EP, whereas for M6 the expression was high only on melon. Overall, our results indicate that the solanaceous strains belong to Group II. To the best of our knowledge, this is the first study that reports characterization of A. citrulli strains isolated from solanaceous species. The fact that A. citrulli is able to naturally colonize and cause disease in non-cucurbit crops poses additional challenges for management of this important pathogen.     

拔节后补灌对不同穗型冬小麦耗水和籽粒产量的影响

为探究拔节期和开花期不同补灌方案对不同穗型冬小麦耗水特性、籽粒产量和水分利用效率的影响，于2017-2019年在山东省泰安市以大穗型品种山农23和中多穗型品种山农29为试验材料，以拔节后无灌水(T1)为对照，设置拔节期补灌目标为0~20 cm土层相对含水率达100%田间持水率(T2)、拔节期和开花期补灌目标为0~20 cm土层相对含水率达100%田间持水率(T3)和拔节期补灌目标为0~40 cm土层相对含水率达100%田间持水率(T4) 3种补灌方案。结果表明，拔节后不同补灌方案对大穗型和多穗型小麦品种影响基本一致。与T1处理相比，T4处理显著提高了0~100 cm土层土壤相对含水率，使60~100 cm土层土壤相对含水率在开花期仍保持较高水平；T3处理显著提高了拔节期0～60 cm和开花期0~40 cm土层土壤相对含水率。与T3处理相比，T4处理的拔节至开花阶段耗水量增加了28.9%，其中对上层土壤总供水的表观消耗量增加了66.4%；T4处理在开花至成熟阶段对深层土壤总供水的表观消耗量增加了68.0%，对上层土壤总供水的表观消耗量降低了37.4%。在开花至成熟期降水较多(121.2 mm)的年份，T4处理的开花至成熟阶段耗水量、开花后旗叶净光合速率和籽粒产量相对于T3处理均无显著变化，但总耗水量较高，水分利用效率显著降低；在开花至成熟期降水较少(45.2 mm)的年份，T4处理的开花至成熟期的阶段耗水量、开花后旗叶净光合速率、籽粒产量和水分利用效率较T3处理均显著降低。因此，在小麦全生育期降水量为111.6~220.2 mm、开花后降水量为45.2~121.2 mm的条件下，大穗型和中多穗型小麦品种均以在拔节期和开花期将0~20 cm土层补灌至100%田间持水率的补灌方案最优，可同时实现高产和高水分利用效率。     

Genetic and environmental influences on chickpea water‐use efficiency

Chickpea is a major crop grown for its nutritional value, and it is used for both food and feed. However, terminal drought greatly reduces grain yield in many chickpea producing areas. The impacts of drought could be mitigated by adapting chickpea genotypes with higher water‐use efficiency (WUE). To assess genetic variation for WUE, contrasting genotypes were sown in two moisture regimes (well‐watered and water‐limited) and two tillage regimes (tillage and no‐tillage) in north‐western NSW across two consecutive seasons. The well‐watered and no till treatments were higher yielding than their respective rainfed and tillage treatments. Genotypes did not differ (p < 0.05) in their water use but differed significantly in their WUE, and a significant genotype‐by‐moisture treatment effect was observed. The heritability of WUE was higher under tillage (71.3% for tillage under rainfed conditions and 73.0% for tillage and irrigated conditions) than no‐till (43.3% for no till under rainfed conditions and 36.4% for no‐till and irrigated conditions), and no significant genotype‐by‐tillage interaction was observed.     

Nutritional and mineral content of prickly pear cactus: A highly water‐use efficient forage,fodder and food species

Increased demand for food requires us to investigate livestock forage and fodder crops that can be grown over a wide range of locations where their cultivation will not compete with that of the food supply. A large portion of the southwestern United States consists of underutilized semi‐arid land. Crops typically used for livestock fodder or forage have high‐water demands that make them uneconomical or unsustainable for semi‐arid and arid regions. The growth rate and low‐input requirements of prickly pear cactus (Opuntia ficus‐indica) make it an excellent candidate for forage or fodder supplementation or replacement in these regions. Previous reports about forage quality data on Opuntia have been scattered across multiple locations, growing conditions and cultivars. Here, we report on the forage quality and mineral content of Opuntia ficus‐indica grown under both field and greenhouse conditions. Crude protein was 71 and 264 g/kg of dry mass for field and greenhouse conditions, respectively. Field‐grown plants showed higher acid and neutral detergent fibre content than greenhouse‐grown plants reflecting higher cellulose, hemicellulose and lignin accumulation. Nutritional values were also compared to requirements of cattle to determine what deficiencies might need to be addressed through supplementation. These data suggest that Opuntia can be used in combination with other feed sources to reduce the demand of resource‐intensive forage crops for raising livestock in dryland areas.     

麦/油-稻轮作下秸秆还田与氮肥管理对直播杂交稻氮素利用特征的影响

【目的】探明秸秆还田和氮肥管理对麦/油后直播杂交稻氮素积累、转运、氮肥利用效率及籽粒产量的影响。【方法】选用优质三系杂交稻宜香优2115,采用二因素裂区设计,麦、油茬田同步开展试验,处理完全一致。主区为麦/油秸秆全量翻埋还田(M₁)和秸秆不还田(对照,M₀),副区设4个氮肥管理,即不施氮对照(N₀)、m_基肥∶m_分蘖肥∶m_促花肥∶m_保花肥比例分别为1∶0∶0∶0(N₁)、3∶3∶2∶2(N₂)、2∶2∶3∶3(N₃),测定了直播杂交稻主要生育时期各器官的氮素积累量及籽粒产量。【结果】结果表明,两种轮作方式下,氮肥管理对直播杂交稻主要生育时期的氮素积累、齐穗后茎鞘、叶片的氮素转运及稻株氮素利用效率均存在显著或极显著的调控效应。秸秆还田显著提高麦/油茬杂交稻中后期的氮素积累量、茎鞘和叶片的氮素转运量以及氮肥利用效率,其中,氮肥农学利用率、氮肥偏生产力和氮肥表观利用率较秸秆不还田分别提高了34.96%/28.76%、2.52%/2.61%和31.91%/22.30%。同时,油菜秸秆还田下直播杂交稻各生育时期氮素积累和产量较麦秆还田表现更好,籽粒产量提高481 kg/hm²(5.22%)。M₁N₂处理、M₀N₃处理下,直播杂交稻各阶段的氮素积累速率明显加大,促进结实期茎鞘和叶片的氮素向穗部转运,成熟期稻株氮素积累量优势明显且有较高的氮素利用效率(麦/油茬稻氮肥农学利用率、偏生产力和表观利用率分别达17.87 kg∙kg^-1/17.85 kg∙kg^-1、67.27 kg∙kg^-1/71.28 kg∙kg^-1、74.93%/75.05%),最终实现高产。【结论】在麦/油-稻轮作下秸秆全量还田,配合N₂氮肥管理,可有效提高直播杂交稻氮素吸收、利用效率,增加籽粒产量,尤以油菜秸杆还田的效果更好。     

夏玉米产量时空变化及气候年型分析

定量分析夏玉米同一品种产量及产量构成要素时空变化,探讨造成产量时空差异的气候年型组合变化特征。基于2004～2013年夏玉米种植区郑单958多点田间试验数据分析表明,夏玉米区域平均产量为9 055 kg/hm~2,年际差为1 635 kg/hm~2,变幅为18.1%;地点差4 258 kg/hm~2,变幅为47.1%。夏玉米区域平均千粒重为313 g,年际变幅为13.1%;地点变幅为27.8%。夏玉米区域平均穗粒数为479,年际变幅为18.0%,地点变幅为38.7%。千粒重的增加导致夏玉米产量显著增加。穗粒数显著降低和时空差异大是造成产量波动和时空差异变幅大的主要原因。夏玉米产量和产量构成要素,低产点受各气候要素变化的影响显著;平产点受温度和日最高温度大于33℃的天数影响显著;高产点受降水影响显著。     

喀斯特山区不同土地利用方式下石灰土化学风化特性

研究喀斯特山区不同土地利用方式（耕地、荒草地、退耕还草地和林草间作地）石灰土剖面化学风化特征，探讨矿质元素在石灰土剖面的分布、迁移和富集特征，从不同土地利用方式下土壤风化度，元素淋溶度、迁移度和残积度的角度分析土壤化学风化特征。结果表明：喀斯特山区石灰土剖面氧化物含量以SiO₂、Al₂O₃、Fe₂O₃为主，其他氧化物含量相对较低，均属于中等变异元素，SiO₂、Al₂O₃、MgO含量以荒草地较高，CaO、Na₂O含量以林草间作地较高，Fe₂O₃、MnO、P₂O₅、K₂O以耕地较高；研究区土壤处于中等化学风化阶段，富铝化程度弱，不同土地利用方式下荒草地土壤化学蚀变系数较强，林草间作地土壤富铝化程度较高；研究区土壤K、Na、Ca淋失严重，荒草地盐基离子淋失明显，林草间作地盐基离子淋失程度相对较低；土壤Fe、Al相对富集明显，残积程度高，林草间作地Al含量积累明显，退耕还草地Fe含量富集显著；实施“退耕—还草”等增加植被覆盖度的治理模式对土壤的保护作用显著。     

新疆南疆机采棉品种株型结构与产量性状的相关性

【目的】分析不同类型陆地棉品种的株型结构及产量性状,研究高产优质机采棉品种的株型结构与产量结构的特点,为棉花结构育种提供理论参考。【方法】测试不同机采棉品种的株型结构性状及产量结构相关指标,利用差异显著性分析、相关分析等统计方法,研究几种机采棉品种的株型性状、产量结构性状及其相关性特点。【结果】籽棉产量与株高、主茎节间长、果枝数、果节数存在正相关但不显著,与果枝始节高度呈负相关;株高与果枝始节高存在显著正相关,与主茎节间长度呈极显著相关; 17N11株型为塔型结构,其底部主茎叶片保留完整、籽棉产量、株高最高,而17N13主茎叶片数最多,17N5则具有最小的叶片脱落率;在棉花株型结构的共性方面,棉花果枝角度具有由上至下呈增大趋势,而变异能力则呈现与之相反的趋势(上部＞中部＞下部)。棉花主茎叶大小具有由上部至下部减小的趋势,变异能力亦呈现与之相反的趋势(下部＞中部＞上部)。【结论】株型结构具备中、上部果枝夹角较小(上部＜32.0°,中部＜50.0°),主茎叶总面积高于320 cm²,下部主茎叶片脱落率低于20%的机采棉品种产量优势显著,中上部果枝夹角、主茎叶总面积、下部主茎叶片脱落率可作为株型育种后代材料选择依据。     

Towards the sustainable intensification of agriculture—a systems approach to policy formulation

The sustainable intensification of agriculture involves providing sufficient food and other ecosystem services without going beyond the limits of the earth’s system. Here a project management approach is suggested to help guide agricultural policy to deliver these objectives. The first step is to agree measurable outcomes, integrating formal policy goals with the often much less formal and much more diverse goals of individual farmers. The second step is to assess current performance. Ideally, this will involve the use of farm-scale metrics that can feed into process models that address social and environmental domains as well as production issues that can be benchmarked and upscaled to landscape and country. Some policy goals can be delivered by supporting ad hoc interventions, while others require the redesign of the farming system. A pipeline of research, knowledge and capacity building is needed to ensure the continuous increase in farm performance. System models can help prioritise policy interventions. Formal optimization of land use is only appropriate if the policy goals are clear, and the constraints understood. In practice, the best approach may depend on the scale of action that is required, and on the amount of resource and infrastructure available to generate, implement and manage policy.