Simulated N management effects on corn yield and tile-drainage nitrate loss

Thoroughly tested simulation models are needed to help quantify the long-term effects of agriculture. We evaluated the Root Zone Water Quality Model (RZWQM) response to different N management strategies and then used the tested model with observed weather data from 1961-2003 to quantify long-term effects on corn (Zea mays L.) yield and flow weighted nitrate-N concentration in subsurface “tile” drainage water (Nconc). Fourteen years (1990-2003) of field data from 30, 0.4 ha plots in northeast Iowa were available for model testing. Annual crop yield, nitrate-N loss to subsurface “tile” drainage water (Nloss), Nconc, and subsurface “tile” drainage amount (drain) for various management scenarios were averaged over plots and years to create five chemical fertilizer and five swine manure treatments. Predicted corn yield and Nconc for the 10 treatments were significantly correlated with observed data (R² > 0.83). The Root Mean Square Errors (RMSE) were 15% and 18% of its observed average Nconc for chemical fertilizer and manure treatments, respectively. Corresponding RMSEs for corn yields were 8% and 10% of its observed average corn yields for chemical fertilizer and manure treatments. The long-term simulations indicate that average corn yield plateaus and Nloss accelerates as quadratic functions of increasing spring UAN-N rates from 100 to 200 kg N/ha. Winter wheat (Triticum aestivum L.) sowed after corn and soybean [Glycine max (L.) Merr.] harvest was predicted to reduce long-term Nloss by 5 to 6 kg N/ha, which appears consistent with published field studies and may be a treatment to ameliorate agricultural management with potential for elevated Nloss such as swine manure application to soybean. The results suggest that after calibration and thorough testing, RZWQM can be used to quantify the relative effects of corn production and Nconc under several alternative management practices.     

Effects of no tillage and genetic resistance on sunflower wilt by Verticillium dahliae

From 2001 to 2006 crop seasons three field experiments were run to compare the effect of no tillage (NT) vs. conventional tillage (CT) on Verticillium wilt of sunflower. One experiment had sunflower monocropping (SM) and the others the sequence wheat–sunflower (WS) with 6 years of fescue pasture or seven WS cycles as previous crops. All experimental fields have history of the disease. One cultivar with low resistance was used in SM and two genotype-resistance levels (high and low; characterized by six and eight cultivars each, respectively) in the WS sequences. Leaf mottle severity in all environments, Verticillium dahliae colony forming units (CFU)/g of soil in 2005 or 2006 trials, density of microsclerotia in the stem pith at 0.5 m above the soil line in WS, and grain yield and oil content in WS with fescue as previous crop were recorded. Every year, disease severity was higher in CT than in NT in all trials. In SM, disease severity increased during the 3 years in CT from 58% to 88%, while in NT disease severity remained around the initial level (49%). The V. dahliae-CFU/g of soil after 3 years in SM or three cycles of WS was approximately three times higher in CT than in NT. In WS, density of microsclerotia in stem pith were higher in CT than in NT. In WS with fescue pasture as previous crop, grain yield and oil content tend to increase with NT in relation to CT. The combination of NT and high-resistant genotypes reduced the disease and the production of microsclerotia in stem pith to very low values. NT + high resistance should be viewed as a preventative, not a curative disease management option because the microsclerotia persist in soil for a long time. Therefore, NT + high resistance programs should be initiated early, before inoculum builds up to high levels in the soil. Thus, the combination of NT and high-resistant cultivars promises to be an interesting tool to manage V. dahliae and Verticillium wilt in sunflower and would have potential in other crops like alfalfa, cotton or strawberry.     

高寒草甸蒸散量及作物系数的研究

利用FAO Penman-Monteith计算法(FAO P-M法)、Penman修正公式法(P法)、Irmark-Allen拟合公式法(I-A法)分别计算了海北高寒草甸参考作物蒸散量,并以FAO P-M法计算结果为标准,与其它两种方法的结果进行比较。结果表明,海北高寒草甸地区年参考作物蒸散量为812.0mm,其中植物生长季的5-9月为500.9mm。FAO P-M法计算参考作物蒸散量较为合理,造成其他两种方法计算结果偏差的原因主要是辐射项的选取及土壤热通量的影响。利用实测土壤含水量资料和水量平衡方法计算的植物生长期的5-9月植被实际蒸散量为425.5mm,与FAO P-M法得到的参考作物蒸散量相比计算作物系数,得到植物生长初期、中期和末期的作物系数分别为0.51、0.96和0.87。     

SSR分子标记在作物遗传育种中的应用

SSR（simple sequence repeat）是建立在PCR技术上的一种广泛应用的分子标记,具有含量丰富、多态性高、共显性等优点。本文简要介绍了SSR分子标记技术的原理和特点,重点介绍了SSR分子标记技术在作物遗传育种中的应用,主要在作物遗传多样性、基因定位、分子辅助标记、遗传图谱构建、品种鉴定和纯度鉴定等方面进行阐述。     

新乡地区冬小麦缺水量适宜估算模式研究

作物缺水量是确定灌溉需水量和制定灌溉制度的基础依据。利用新乡地区连续两个冬小麦生长季(2005~2006年、2006~2007年)田间试验资料建立了冬小麦生育期叶面积指数增长模型、需水量估算模型和土壤入渗模型。在此基础上, 根据新乡地区51年(1951~2001年)的逐日气象资料, 采用土壤水分平衡法, 综合考虑作物蒸散、降水和灌溉等因素, 模拟冬小麦各生长季降水有效利用状况, 分析研究该地区连续50个冬小麦生长季降水量与相应时间段有效降水量间的相互关系, 确定不同时间尺度下有效降水量估算模式。最后, 以确定的作物需水量和有效降水量估算模式为基础, 提出河南新乡地区不同时间尺度下的冬小麦缺水量适宜估算模式。     

土壤环境质量指导值与标准研究 Ⅴ.镉在土壤-作物系统中的富集规律与农产品质量安全

通过查阅国内现有镉污染农田土壤和作物中镉含量的相关资料,包括近30年来公开发表文献、国家"七五"科技攻关环保项目"土壤环境容量研究"等科研成果,结合本实验室在长江三角洲、珠江三角洲典型地区污染农田调查数据,经筛选后从88组研究中共收集到镉污染农田土壤和作物中镉含量对应数据509对。根据镉盐来源,将收集的数据分为污染农田调查数据和添加镉盐试验数据;根据作物不同,分为水稻、小麦、茎/叶类蔬菜、根菜和果菜地调查数据。采用富集系数和一元回归模型的方法基于土壤镉含量预测作物可食部分镉含量;采用多元回归模型的方法基于土壤镉含量和土壤pH预测作物可食部分镉含量。结果表明,回归模型对作物可食部分镉含量的预测效果明显优于富集系数中位值;回归模型95%预测上限对作物可食部分镉含量的保守预测优于富集系数90分位值。土壤pH显著影响作物对镉的吸收。影响模型回归效果和预测能力的主要因素是数据分布不均和数据量不足。模型对比后选用多元回归模型的95%预测上限推导稻田和茎/叶类蔬菜用地基于农产品质量安全的土壤镉含量环境基准。     

大气[CO2]和温度升高对农作物生理及生产的影响

全球大气[CO2]和气温升高是全球气候变化对农作物产量影响最为重要的两个因子。本文着重介绍了[CO2]和温度升高对农作物光合作用、呼吸作用、蒸腾作用、产量、品质等方面影响的研究进展。研究表明随着[CO2]升高,作物光合速率及蒸腾速率有上升趋势,呼吸作用和气孔导度下降,产量有所提高,品质将会降低,但研究仍有不确定性。随着[CO2]变化,不同光合途径(C3、C4)作物的响应不一致且存在短期和长期效应。普遍认为大气温度升高抑制作物光合作用,作物产量下降。现有的研究多采用模型或模拟试验的方法研究气候变化对作物产量的影响,但研究发现模型研究结果与模拟试验研究结果有差异,不同学者对产量的评估结果也不一致。最新研究认为温度对作物产量影响成非线性,当温度高于关键温度后产量会迅速下降。现阶段大部分模拟试验均在气室中研究,与野外实际情况差异较大,结论仍需进一步验证。目前尚缺乏对作物模型结果的实验验证。     

有机肥料氮替代部分无机氮对水稻产量的影响及替代率研究

通过田间试验,研究了不同氮用量下有机肥料氮替代部分无机氮对水稻产量、氮肥利用率和土壤矿质态氮的影响,试图探索出有机肥料氮替代无机氮的最适替代率,并对有机肥与化肥配施的经济效益进行评价。结果表明:1）有机肥与化肥配施处理（8381~9810 kg/hm2）能获得与单施化肥处理（8381~10124 kg/hm2）更高或持平的产量;2）与单施化肥相比,氮用量在N 240 kg/hm2内,有机肥料氮替代无机肥料氮的最适替代率为10%~20%（相当于施用1500~3000 kg/hm2商品有机肥）,此时水稻产量、氮肥利用率和经济效益都达到最佳水平;3）与单施化肥相比,氮用量在N 240 kg/hm2以内并且有机肥料氮占氮总量的10%~20%时可以获得较为平稳的氮素供应过程,改善了土壤供氮能力。上述结果可为研制有机无机复合肥提供理论基础。     

Comparison of empirical daily surface incoming solar radiation models

Most environmental and agronomic models use climatic inputs such as temperature, solar radiation and rainfall. In Canada, few automatic weather stations can monitor incoming solar radiation. Hence, surface incoming solar radiation must be estimated from other meteorological data. The aim of the present research was to conduct a comparative study of three empirical models for the estimation of surface incoming solar radiation on a horizontal surface. The first two methodologies use the traditional and long-utilized linear approach based on latitude and daily temperature range. A more recent methodology uses neural networks (NN) to build a similar regression based on latitude and temperature range, but providing more flexibility in the formulation as well as a non-linear activation function. Global daily solar radiation data from 11 stations located in northeastern America was used to optimize and test the different models. Even though coefficients of the classical models were locally optimized using a standard unconstrained non-linear scheme, NNs markedly improved the estimation of incoming surface solar radiation.     

间套作强化农田生态系统服务功能的研究 进展与应用展望

间套作是我国传统农业的精髓,其存在2 000多年,必然蕴含重要的科学原理。过去的研究表明其不仅能够大幅度提高作物产量,而且能够充分利用地上部的光热资源,充分挖掘和利用地下部水分养分资源,强化农田生态系统服务功能。近年来,国内外对其资源高效利用的研究取得了显著的进步,特别是地下部资源高效利用方面。本文首先综述了相关研究的进展:间套作作为增加农田生态系统生物多样性的重要措施,具有重要的生态功能,如提高作物产量,增加作物生产力的稳定性,充分利用地上部光热资源和土壤水分、土壤和肥料中的氮素和磷素以及微量元素等。随后,对间套作提高资源利用效率的机制进行了分析,包括水分需求上的时间和空间生态位互补,豆科/禾本科间作体系中的豆科作物生物固氮和禾本科作物对土壤氮素利用上的互补和促进作用;磷活化能力强弱搭配的间作体系中,磷活化能力强的作物对活化能力弱的作物的促进作用;双子叶和单子叶植物的搭配,改善双子叶植物的Fe、Zn等微量元素的含量等。最后,对间套作进一步研究方向和应用提出了一些看法和思路。在研究方面,包括作物多样性与农业可持续发展,地下部作物种间信号的传递,地上地下部多样性的互反馈调节机制,以及作物生长模型等。在应用方面,包括豆科作物纳入农业生产体系发展生态集约化农业,利用间套作发展有机农业,利用种间相互作用提高磷肥利用率和增加作物可食部分的微量元素含量等。并认为间套作中的机械化、育种等问题的解决将有利于间套作的进一步发展。