粮食安全视角下东北地区耕地利用功能转型特征研究

系统考察东北地区耕地利用功能转型对粮食生产的影响,有助于从国家全局层面把握耕地与粮食之间的关系,从而为我国实现农业现代化和粮食安全高质量发展提供科学参考。本文基于2011—2020年全国省级面板数据,采用熵权法、双固定模型等估计方法,明晰东北地区耕地利用功能转型特征及其影响国家粮食安全的作用机制。结果表明：2011—2020年,我国粮食安全水平呈上升态势,东北地区耕地利用功能转型有效赋能全国粮食安全。在地区异质性研究中,辽宁省、黑龙江省耕地利用功能转型的粮食安全保障效应更加明显,吉林省作用渠道有待畅通。在维度异质性研究中,东北地区耕地利用功能转型主要通过促进粮食数量安全和粮食经济安全保障我国粮食安全,粮食生态质量保障效应不明显。据此,为了使东北地区耕地利用功能转型更好地促进国家粮食安全,从提供东北地区耕地利用与粮食生产经济补贴、因地制宜制定东北地区耕地利用功能转型策略、打造以生态质量为导向的“优质粮食工程”等方面提出建议。     

Antioxidation responses of maize roots and leaves to partial root-zone irrigation

Antioxidation responses of maize roots and leaves to water deficit and rewatering under partial root-zone irrigation (PRI) were investigated using a pot system. Plants were cultured using three irrigation methods, i.e. conventional irrigation (CI), alternate PRI (APRI) and fixed PRI (FPRI) with three different water regimes including W₁ (70% field capacity, FC), W₂ (50% FC) and W₃ (35% FC). Compared to CI, root peroxidases (POD) activity was enhanced in the irrigated root zone of FPRI and both root zones of APRI during mild water deficit. After rewatering, POD activity was increased in the dry root zone under FPRI but reduced in the roots under APRI. Roots in the dry zone and leaves under FPRI remained high superoxide dismutase (SOD) activity after rewatering. In contrast, SOD activity decreased in the roots and leaves under CI and APRI. Malondialdehyde (MDA) contents were increased in leaves and two sub-roots under FPRI during water deficit and remained higher after rewatering compared to those under CI and APRI. MDA contents in the tissues under APRI showed similar levels to those under CI. Compared to CI, APRI showed the same biomass production, achieving significantly higher water use efficiency under mild water deficit. The results suggested that plants under APRI experienced less oxidative stress or damage induced by water deficit.     

2000年~2018年中国食用菌出口国际竞争力分析

利用我国省级面板数据对食用菌出口国际竞争力进行分析,结果表明,近年来我国食用菌出口国际竞争力呈现明显上升趋势,但是我国30个省市间食用菌出口贸易竞争力呈现明显的区域异质性,其中北京、上海、广东等地的食用菌出口贸易竞争力明显高于中部和西部地区。农业产值、城市化水平、食用菌生产规模进口国购买力与食用菌出口国际竞争力之间为显著的正相关关系,而汇率水平、食用菌产品价格与食用菌出口国际竞争力之间为显著的负相关关系。     

杉木种源对断面积模型影响的检验和比较

对鸡公山、大岗山和洪雅种源试验的调查材料,用随机效应检查和固定效应检查两种方法检验和比较了同一地区不同种源对断面积生长模型的影响。结果表明,种源试验中采用随机效应检查较好,固定效应检查容易造成差异显著的误判。随机效应检查的结果表明,同一地区不同种源的断面积模型相同。     

用组合方法证明三维情况的Brouwer不动点定理

通过使用组合方法,Sperner引理以及拓扑基础性质(连续性,紧致性)以及连续的向量场与连续变换之间的关系,来证明3维情况下,Brouwer不动点定理,给出了有别于以往代数拓扑证明新方法.     

Tomato nitrogen accumulation and fertilizer use efficiency on a sandy soil, as affected by nitrogen rate and irrigation scheduling

Tomato production systems in Florida are typically intensively managed with high inputs of fertilizer and irrigation and on sandy soils with low inherent water and nutrient retention capacities; potential nutrient leaching losses undermine the sustainability of such systems. The objectives of this 3-year field study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling on crop N and P accumulation, N-fertilizer use efficiency (NUE) and NO₃-N leaching of tomato cultivated in a plastic mulched/drip irrigated production system in sandy soils. Experimental treatments were a factorial combination of three irrigation scheduling regimes and three N-rates (176, 220, and 330 kg ha⁻¹). Irrigation treatments included were: (1) surface drip irrigation (SUR) both the irrigation and fertigation line placed underneath the plastic mulch; (2) subsurface drip irrigation (SDI) where the irrigation drip was placed 0.15 m below the fertigation line which was located on top of the bed; and (3) TIME (conventional control) with the irrigation and fertigation lines placed as in SUR and irrigation applied once a day. Except for the TIME treatment all irrigation treatments were soil moisture sensor (SMS)-based with irrigation occurring at 10% volumetric water content. Five irrigation windows were scheduled daily and events were bypassed if the soil water content exceeded the established threshold. The use of SMS-based irrigation systems significantly reduced irrigation water use, volume percolated, and nitrate leaching. Based on soil electrical conductivity (EC) readings, there was no interaction between irrigation and N-rate treatments on the movement of fertilizer solutes. Total plant N accumulation for SUR and SDI was 12-37% higher than TIME. Plant P accumulation was not affected by either irrigation or N-rate treatments. The nitrogen use efficiency for SUR and SDI was on the order of 37-45%, 56-61%, and 61-68% for 2005, 2006 and 2007, respectively and significantly higher than for the conventional control system (TIME). Moreover, at the intermediate N-rate SUR and SDI systems reduced NO₃-N leaching to 5 and 35 kg ha⁻¹, while at the highest N-rate corresponding values were 7 and 56 kg N ha⁻¹. Use of N application rates above 220 kg ha⁻¹ did not result in fruit and/or shoot biomass nor N accumulation benefits, but substantially increased NO₃-N leaching for the control treatment, as detected by EC monitoring and by the lysimeters. It is concluded that appropriate use of SDI and/or sensor-based irrigation systems can sustain high yields while reducing irrigation application as well as reducing NO₃-N leaching in low water holding capacity soils.     

水稻土连续施用稻草及氮磷钾肥增产效应的研究

6年的定位试验结果表明:在寒冷稻作区的白浆型水稻土上,土壤有机质含量保持稳定,连续施用化肥可相应提高土壤氮、磷、钾的含量,长期不施某种养分,则土壤中该种速效养分含量呈下降趋势。连续施用稻草可明显提高土壤有机质含量,特明是稻草加氮磷钾处理,土壤有机质及各种养分的增加量明显高于其他处理,而且后四年的水稻产量均居首位,说明化肥与稻草配合施用有较好的改土肥田作用。在该种土壤上连续单施氮肥亦有稳定而极显著的增产效应,磷钾肥增产效果不显著。     

章古台沙地彰武小钻杨造林试验

为了营造生态经济型固沙林,以银中杨、小美旱杨、黑林-1杨和樟子松等树种为对照,选择彰武小钻杨在不同沙丘部位进行造林试验。试验表明:在平缓沙地彰武小钻杨生长量比较高,树高和胸径分别为银中杨的91.8%和104.2%,为黑林-1杨的105.9%和120.6%,为小美旱杨的112.5%和195.2%;在沙丘下部彰武小钻杨比樟子松生长量显著增加;而在沙丘上部比樟子松生长降低,并发生干枯。     

降水在沙丘中的渗透过程研究

观测研究结果表明 :⑴降水在沙丘上下渗深度与降水量及降水强度成正相关 ,与气温成负相关。民勤沙区雨季降水量在 4 0mm以上时在沙丘中的下渗深度可以达到 5 0～ 90cm。在当地 ,秋季降水尤其是秋季连续降水是沙丘储存水分的主要来源。⑵降水在沙丘上的下渗速率与降水量正相关 ,降水量大 ,主要含水层的含水率则高 ,下渗速度自然就快。⑶降水后梭梭根部沙面 0～ 5cm含水率高于流动沙丘 ;降水停止 1d以后对应于流动沙丘的最大含水层梭梭根部的含水率明显降低 ;降水停止 1d后在流动沙丘降水下渗深度内的平均含水率高于梭梭沙丘对应层含水率 ,且随时间推移这个差值在增大。⑷在 0～ 4 5mm的降水量范围内 ,不论是流动沙丘还是有梭梭林的沙丘 ,其降水的主要含水层在表层 0～ 2 0cm范围内。⑸当地 8月上旬 <12mm的降水量在降水停止后的 7～ 8d内蒸发殆尽 ;4 3.5mm的降水量在降水停止后第 10天时 0～ 15 0cm沙层含水率折合水层深度较降水前多 17.2 8mm ;2 1.7mm的降水量在降水停止后第 10天时 0～ 15 0cm沙层含水率折合水层深度较降水前多 10 .6 6mm ;在降水过程中和降水后的 1d内水分蒸发损耗最大     

长期施肥对设施蔬菜栽培土壤易氧化有机碳含量及其剖面分布的影响

对农业可持续发展系统来说,土壤碳库容量是很重要的因子,其变化主要发生在易氧化碳库(EOC)里.在设施蔬菜施肥长期定位试验基础上,研究了长期施用有机肥和化肥对设施内土壤易氧化有机碳的影响.结果表明,除了长期不施肥的土壤外,其它施肥处理土壤易氧化有机碳含量均随着土层深度的增加而降低.A组(有机肥组)各土层以ANP(有机肥+氮磷化肥)处理易氧化有机碳含量最高,其次是ANPK(有机肥+氮磷钾化肥)、ANK(有机肥+氮钾化肥),AN0(单施有机肥)含量最低;B组(不施有机肥组)中BNP(氮磷化肥)易氧化有机碳含量最高,其次是BNK(氮钾化肥)、BNPK(氮磷钾化肥).与不施肥处理相比,长期施用有机肥能够显著提高0-60 cm各层土壤易氧化有机碳的含量,且施用有机肥以及有机肥与氮磷钾化肥配施效果要优于不施有机肥处理.