我国玉米生产现状及发展变革

近年来，随着农业供给侧结构性改革的实施，玉米价格回落，玉米生产出现了高生产、高库存、效益低、卖粮难等突出问题，农民种植积极性受挫，玉米生产面临变革。未来玉米产业如何定位、如何发展，种植面积调减只是第一步，更为重要的是对玉米生产各环节的优化和升级。通过梳理我国当前玉米生产、消费和需求现状，从农业种植结构、劳动力结构变化、生产经营方式、品种创新、质量安全、生产潜力提高等方面进行了分析研究，提出了优化产业结构、稳定玉米生产，适应劳动力变化、加快土地集中耕种、提高种植效益，加快玉米品种原始创新、培育多元优质高效型品种，多措并举、提高玉米安全质量，种养结合、培肥地力、持续提高玉米生产潜力等具体措施。最终实现多元、优质、高产、高效及生态、智慧、可持续的玉米生产现代化。     

中国高粱产业发展特征及趋势分析

高粱是我国重要的杂粮作物。近年来，中美贸易中高粱交易量剧烈波动，高粱供需形势发生显著变化，高粱产业发展备受关注。从中国高粱的生产特征、贸易特征、消费特征等方面入手，对1960-2018年国内高粱产业发展趋势及发展现状进行分析。研究发现，中国高粱从主要粮食作物转变为小杂粮，近年来种植面积略有提高；国内高粱消费主要用于酿酒和饲料，虽然中国是世界第三大高粱消费国，但人均消费水平并不高；目前，中国作为世界第一大高粱进口国，进口量受饲料高粱需求影响猛增猛减，出口量极小且相对稳定。未来，中国高粱的发展规模将保持相对稳定，新的增长空间主要取决于旱作粮食作物的发展和消费途径的拓展。     

文冠果枝叶生长与叶幕微气候的关系研究

【目的】探索叶幕微气候因子对文冠果枝条生长发育和光合同化能力的影响,为文冠果树体的整形修剪提供理论依据。【方法】在山东东营选择20株6年生文冠果树,调查其冠层内东西南北4个方向,每方向上层和下层、外侧和内侧4个区域,共16个小区域的温度、湿度、光照等微气候因子,再分别测定各区域文冠果枝叶量及叶片光合色素、光合产物和氮含量,并将其与微气候因子进行相关性分析。【结果】文冠果叶幕内不同区域温度和湿度均无显著差异,但不同区域光照强度差异显著,除北向上层外侧光照强度略低于下层外侧外,其余各方向均有上层外侧最高、下层内侧最低的现象,两区域差异达260.0%。树冠东、南方向1年生枝条数量、长度、基径均大于西、北方向;树冠上层1年生枝条数量少于下层,而上层1年生枝条长度、基径均大于下层;树冠外侧新枝数量和叶片数量均多于内侧,下层叶片数量多于上层,但上下层新枝数量无明显差异。5月为树冠内新枝数量和叶面积增长最快的时段,树冠上层新枝数量和叶面积增长快且明显大于下层,与光照强度增长规律一致。树冠内叶片叶绿素和类胡萝卜素含量均有西、北方向高于东、南方向的规律;可溶性糖含量、淀粉含量和碳氮比均有外侧大于内侧,东、南方向大于西、北方向,且东、南方向各区域差异较大的规律。光照与文冠果树冠枝、叶生长指标和叶片生理指标相关性较大,且与多数树体枝、叶生长指标和叶片生理指标均呈显著正相关关系,但与光合色素含量无显著相关性。【结论】适当对东、南方向和上层、外侧的枝条加以疏除,可以增强透光性,能使树体生长更为均匀,为文冠果产量提高奠定基础。     

2000年以来中国苹果产业发展趋势分析

对2000年以来我国苹果生产、消费和贸易情况进行分析发现,我国苹果生产区域布局较为稳定,生产高度集中于苹果生产优势区域。苹果生产效率大幅提升,不断满足城乡居民对苹果的消费需求,城乡差距不断缩小,苹果产品贸易顺差进一步扩大。但苹果生产成本利润率显著下降,消费者对苹果品质及营养也提出了更高的要求,苹果生产面临成本、质量等方面的挑战。与此同时,苹果生产中技术服务、农业保险等社会化服务也有了初步发展,未来苹果生产将进一步向高效、优质、社会化发展。     

江西省水稻蓄雨间歇灌溉模式初探

【目的】探索水稻蓄雨间歇灌溉模式节水减排效益。【方法】以鄱阳湖区双季早晚稻为试验材料,采用大田和测坑试验,研究了水稻蓄雨间歇灌溉模式对灌溉定额、排水定额、降雨有效利用率、产量、稻田水分生产率,以及氮、磷排放量的影响,并与间歇灌溉和常规淹水灌溉试验进行了分析比较。【结果】与淹水灌溉、间歇灌溉相比,蓄雨间歇灌溉灌排水量、灌排次数明显减少。双季早晚稻年平均灌水量分别减少975m^3/hm^2和1251m^3/hm^2,年平均灌水次数分别减少8次和7.5次;年平均排水量分别减少729 m^3/hm^2和893 m^3/hm^2,年平均排水次数分别减少5.8次和3.1次;蓄雨间歇灌溉降雨有效利用率明显提高。早稻降雨利用率分别提高12.40%和9.14%,晚稻分别提高6.84%和6.42%;蓄雨间歇灌溉模式下,双季早晚稻总氮排放量年平均减排7.64 kg/hm^2和3.12 kg/hm^2,减排幅度34.93%和14.26%;双季早晚稻总磷排放量0.180kg/hm^2和0.095kg/hm^2,减排幅度37.25%和70.59%。【结论】蓄雨间歇灌溉模式具有明显的节水、减排和提高降雨有效利用率的效果,在我国南方多雨地区具有较强的推广应用空间。     

基于启发式Johnson算法优化BP神经网络的水产养殖产量预测模型

针对水产养殖产量预测难的现状,提出一种基于启发式Johnson算法优化的反向传播神经网络(BPNN)的产量预测模型。该模型在传统BP神经网络的基础上,针对网络训练时间长、易陷入局部最优的问题,通过启发式Johnson算法降低输入神经元维度,再结合试凑法确定神经网络隐层个数,构建启发式Johnson反向传播神经网络(HJA-BPNN)学习预测模型。实验结果表明,该模型在山东省对虾海水养殖产量预测中,预测的均方根误差小于传统BP神经网络和GM(1,1),且学习效率相比传统BP神经网络有所提升。研究表明,该学习预测模型在大量历史数据的模型构造上有更大的优势,能够缩短建模时间,同时获得良好的预测效果,为水产养殖产量预测提供了一种可行的新方法。     

烟属野生种主要植物学性状及黑胫病抗性评价

鉴定了烟属植物野生种生育期等植物学性状特性,评价了供试材料对黑胫病(0号及1号生理小种)的抗性,为开展远缘杂交花期相遇及亲本选配提供了基础数据。在玻璃温室内,本研究针对66份烟属植物野生种的生育期等7个植物学性状的调查,检测了烟碱及钾含量,并对黑胫病(0号及1号生理小种)抗性进行了评价。结果表明:供试材料播种到开花时间(DF)为35.00~357.00 d,平均121.67 d;种子千粒重(TSW)为0.02~0.20 g,平均0.09 g;株高(PH)为11.20~292.75 cm,平均119.19 cm;花冠长度(CL)为1.22~11.50 cm,平均3.98 cm;花冠直径(CD)0.67~7.80 cm,平均2.37 cm;最大叶长(MLL)为6.79~61.15 cm,平均25.17 cm;最大叶宽(MLW)为0.65~35.51 cm,平均11.84 cm。烟碱含量为0.03%~1.81%,平均0.34%;钾含量为0.32%~7.11%,平均3.56%。筛选到N.alata PI42334等11份资源同时抗黑胫病0及1号生理小种。     

Effects of dietary carbohydrate on weight gain and gonad production in small sea urchins,Lytechinus variegatus

In experiment 1, juvenile sea urchins (n = 80, 0.088 ± 0.001 g wet weight and 5.72 ± 0.04 mm diameter) were held individually and fed ad libitum one of three semi‐purified formulated diets (n = 16 individuals treatment^?1). In the diets, protein was held constant (310 g kg^?1 dry, as fed) and carbohydrate level varied (190, 260, or 380 g kg^?1 dry, as fed). Wet weights were measured every 2 weeks. Total wet weight gain was inversely proportional to dietary carbohydrate level and energy content of the respective diet. In experiment 2, sea urchins (5.60 ± 0.48 g wet weight, n = 40) fed 190 g kg^?1 carbohydrate consumed significantly more dry feed than those fed 260 g kg^?1, but not more than those fed 380 g kg^?1 carbohydrate. Based on differential feed intake rates, sea urchins that consumed more feed also consumed higher levels of protein and had the highest weight gain. Consequently, protein content and/or protein: energy ratio may be important in determining feed utilization and growth among sea urchins in this study. The average digestible energy intake was approximately 70 kcal kg^?1 body weight day^?1, suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.     

Effects of egg stocking density on egg hatchability,larval quality and water quality for pinfish,Lagodon rhomboides,and pigfish,Orthopristis chrysoptera

Pinfish (Lagodon rhomboides Linnaeus) and pigfish (Orthopristis chrysoptera L.) are relatively new, cultured species commonly used as marine baitfish in the south‐eastern United States and currently have no defined protocols for egg incubation. Thus, experiments were conducted to determine efficient egg stocking densities during static and flow‐through incubation that yielded higher quality larvae. Eggs of each species were incubated statically at 250, 500, 1000 and 2000 eggs L^?1, and after incubation, egg hatching success, larval survival to first feeding, larval morphometrics and water quality were assessed. Stocking densities above 250 eggs L^?1 led to significant reductions in pinfish hatching success and water quality degradation, evident from decreased dissolved oxygen and pH levels and increased nitrogenous wastes. Increased stocking densities for pigfish also resulted in significant water quality degradation, although hatching success was unaffected up to a density of 1000 eggs L^?1. A high flow‐through water exchange rate of 2000% daily resulted in significant reductions in nitrogenous wastes and greater stability in dissolved oxygen and pH levels during incubation when compared to static treatments of the same egg density. Additionally, the high exchange rate of 2000% was critical in maintaining high hatching success and larval survival to first feeding at stocking densities of 1000 eggs L^?1 for pinfish and up to 4000 eggs L^?1 for pigfish. No clear patterns in larval morphometrics were observed among stocking densities. Static incubation densities of 250 and 1000 eggs L^?1 are recommended for pinfish and pigfish, respectively.     

Effects of blue shrimp Litopenaeus stylirostris and goldlined rabbitfish Siganus lineatus in mono‐ and polyculture on production and environmental conditions

This study was conducted to compare the effects of shrimp and rabbitfish in mono‐ and polyculture stocked at high biomass on production and environmental conditions in a mesocosm system. Shrimp (14 g) and/or rabbitfish (19 g) were stocked in four treatments with different density but with the same total biomass (236 g m^?2), including shrimp monoculture (SM) (17 shrimp m^?2), shrimp–fish polyculture (SF) (11 shrimp and 4 rabbitfish m^?2), fish–shrimp polyculture (FS) (6 shrimp and 8 rabbitfish m^?2) and fish monoculture (FM) (12 rabbitfish m^?2). After 10 weeks of experiment, shrimp survival and biomass were low in the treatments where shrimp were dominant (SM, SF), while rabbitfish survival and biomass were high in all the treatments. Shrimp mortality was assumed to be related to an excess of the system carrying capacity (CC). Results suggested that CC is linked to shrimp biomass/density rather than the system eutrophication level. The ecosystem became heterotrophic as daily feed supply was beyond 7 g m^?2 per day. This threshold corresponded to the environmental CC of the semi‐intensive shrimp culture system. Under these conditions, the combination of high fish biomass and low shrimp biomass appeared as the most valuable in terms of system performances.