Yield and seasonal water productivity of sunflower as affected by tillage and cropping systems under dryland conditions in the Limpopo Province of South Africa

Sustainable food production in semi-arid tropical countries can be achieved through efficient utilization of rainwater. A field experiment to assess the grain yield, seasonal water use (WU), water use efficiency (WUE) and precipitation use efficiency (PUE) of sunflower (Helianthus annuus L.) intercropped with cowpea (Vigna unguiculata L.) on two tillage systems was conducted during the 2007/2008 and 2008/2009 cropping seasons at the University of Venda (22°58′ S, 30°26′ E at 596 m above sea level). The experiment was configured as a 2 × 2 × 2 factorial design with three replications. The tillage treatments were conventional tillage (CT) (control) and in-field rainwater harvesting (IRWH) system. The IRWH is a special crop production technique that promotes runoff on 2.0-m wide no-till strip between crop rows and collects the runoff water in basins where it infiltrates into the soil profile. The treatments in the cropping system (CS) consisted of a sole crop (sunflower or cowpea) and an intercrop (sunflower × cowpea). Results of the experiment revealed that IRWH led to a significant (P < 0.05) increase in sunflower grain yield in the second season but cowpea grain yield was not influenced by tillage systems. IRWH resulted in significantly higher WU, WUE and PUE of both crops compared to CT system in the second season. The CS had significant effects on sunflower grain yield in both seasons but none on the cowpea grain yield. WU was significantly higher in intercrops than in sole cowpea and sole sunflower in the first and second season, respectively. WUE and PUE were significantly greater in sole sunflower than in the intercrops but less in the sole cowpea than in the intercrops.     

Use of a process-based model to describe spatial variation in Pinus radiata productivity in New Zealand

The process-based model CenW was used to model the growth of Pinus radiata in New Zealand. The model was parameterised by comparison with data from 101 permanent sample plots, consisting of 1309 individual observations of stands at different ages of up to 32 years. The data covered the range of conditions under which P. radiata is grown in New Zealand. Observations consisted of stand density, and height and/or basal area. Input parameters consisted of site water-holding capacity, soil texture and soil nitrogen concentration, and daily records of minimum and maximum air temperatures, precipitation, solar radiation and atmospheric humidity. Using the same plant parameters for the full data set from all locations, we obtained excellent correspondence between predictions and observed data. Model efficiencies ranged from 0.828 to 0.892 for four growth indices that were either directly observed (height, basal area) or derived from the data (stand volume, mean stem diameter).Within New Zealand, stand productivity was found to be particularly sensitive to mean annual air temperature and mean total annual precipitation, with optima reached from 12-15 °C and 1500-2000 mm, respectively. Productivity exhibited little sensitivity to site fertility as soil nutrition was generally adequate for most sites. Spatial projections showed highest productivity in the moderately wet, warm northern and western regions of the North Island and lowest for cold sites at higher elevation, dry eastern areas of the South Island and the extremely wet sites on the West Coast of the South Island. The model runs provided robust estimates of productivity across the diverse environmental conditions in New Zealand.     

Tree cavities in forests - The broad distribution pattern of a keystone structure for biodiversity

We explored the main factors affecting the global distribution of tree cavities - a habitat component of mostly biotic origin that is crucial for many animal species. We considered the influence of eight environmental variables (ranging from the single-tree to the biogeographic-region scale) on cavity density in a meta-analysis of 103 published studies. The global median density of cavities was 16 ha⁻¹, with densities highest in Australasia and lowest in the Palaearctic region. Two major factors influencing density were identified: cavity density was positively related to the amount of precipitation, and was higher in natural than in managed forests. These effects suggest that the distribution of tree cavities largely reflects the incidence of fungal heart-rot in trees, and that forest management, by affecting wood decay processes, can have a broad-scale impact on tree microhabitat availability. Although air temperature, forest composition and wood hardness had suggestive univariate effects, neither these variables nor biogeographic region explained any additional variation in multifactor models. In regions where woodpeckers are present there was an upper limit to the density of woodpecker-excavated cavities (approximately 10-20 cavities ha⁻¹) that was considerably lower than the highest total cavity densities encountered (up to 140 ha⁻¹). This indicates that primary cavity-nesters are particularly important keystone species in cavity-poor forests where wood decay processes are suppressed either climatically or by forest management.     

西藏地区降水资源评价与农田水利建设的建议

西藏高原自然降水不多，干湿季明显，干旱频率高；近三十多年来气候有变干的趋势；水资源丰富，但利用率很低。干旱缺水是农业生产的主要制约因素；为较大提高农业生产水平，提出了因地制宜开展农田水利建设的建议。     

山区局地气候的小网格研究方法

山区局地气侯除受宏观地形因子影响外，还要受复杂的小环境的影响。为了进一步分析山区局地气侯的差异，更好地对山区自然资源进行开发，应用小网格方法，引入地形因子，修定气候学方程，采用数学方法建立１ｋｍ热量、降水方程；对北京山区进行分析计算的结果表明，它较好地反映了地形对气候资源的影响，基本符合实际情况，月平均温度误差不超过０．６℃，年降水量绝对误差不超过４０ｍｍ，有一定的实用价值。     

相依自然降水序列干湿游程特征量的模拟分析

以游程理论中ＳｅｎＺ．的方法为基础，研究了相依自然降水序列的主要干湿游程特征量──有限样本长度，给定截取水平的交互点数，干湿游程长的期望值，正、负游程和的期望值等的理论模拟模式。并以郑州１０年逐旬降水序列对模拟结果进行了验证，理论与实际结果具有较好的一致性。     

Precipitation chemistry at sinhagad-a hill station in India

The chemistry of precipitation in remote sites such as mountain tops is of interest in the study of atmospheric pollution and acid rain. The chemical composition measured at mountain site which is away from industrial and urban areas is useful as a reference level and it allows to determine the extent of anthropogenic contamination. Hence, rain water samples were collected at Sinhagad (18°21N, 73°45E, 1450 m asl during the monsoon season (June-September) of 1992 and were analysed for major ions. The precipitation samples collected at Sinhagad were alkaline in nature and pH values ranged between 5.9 to 6.76. The ionic composition was dominated by soil dust The concentration of Ca²⁺ was highest among all the ions. The concentrations of excess SO₃ ^2– and NO₄ ^– were small (23.8 and 15.2 eq l^–1 respectively) compared to the values of polluted regions in India. The correlation coefficient between the ions and pH values was calculated and it was found to be maximum in case of Ca²⁺. Precipitation samples collected at Sinhagad were alkaline owing to higher concentration of Ca²⁺ and lower levels of acidic pollutants (SO₄ ^2– and NO₃ ^–).     

Precipitation chemistry in Japan 1989–1993

Precipitation chemistry in Japan was discussed on a wet-only sample database obtained in a nationwide survey from April 1989 to March 1993. Wet-only samples were collected at 29 stations over Japan on a biweekly basis. Commonly determined chemical parameters were measured in laboratories. The volume-weighted annual mean pH at each site ranged from 4.50 to 5.83 with a mean of 4.76. Concentration ranges and means (parenthesized) on an equivalent basis for major ions were as follows: nss-SO₄ ^2–; 5.2–58.9 (38.6), NO₃ ^–; 1.8–25.0 (14.1), NH₄ ⁺; 0.55–29.8 (18.3), nss-Ca²⁺; 2.0–34.5(14.2), Na⁺; 6.4–275.3 (49.1), Cl^–; 13.7–322.4 (63.5) eq L^–1. Acid-base relationships for Phase-II records were quantitatively discussed in terms of three measures: pH, fractional acidity, and our proposed pA_i.     

高寒山区地形序列土壤有机碳和无机碳垂直分布特征及其影响因素

地形、生物气候条件具有明显差异的青藏高原约占我国陆地面积的五分之一,开展该地区土壤有机碳和无机碳分布特征的研究对于理解青藏高原土壤碳循环过程与陆地碳库的精确预测以及应对全球气候变化具有重要意义。研究选取位于祁连山中段的阴、阳坡地形序列土壤,分析了不同坡向间以及同一坡向内随海拔高度变化土壤有机碳和无机碳的垂直分布特征及其影响因素。结果表明:阴、阳坡有机碳含量均随土壤深度增加而下降,但阳坡下降的速率(66%~91%)明显高于阴坡(31%~77%);阴坡土壤中碳酸钙基本淋失,通体无机碳含量较低(5.0 g kg-1),阳坡B层土壤无机碳含量是A层的2倍,表现为明显富集。阴坡和阳坡1 m土体总碳密度相当(分别为16.1~33.9 kg m-2和11.8~32.8 kg m-2),其中,阴坡以有机碳为主(占总碳密度的82%~99%),而阳坡有机碳和无机碳密度变化均较大(分别占总碳密度的27%~81%和19%~73%)。因此,坡向是影响高寒山区土壤碳垂直分布和组成的重要因素。此外,降雨量和植被类型对地形序列土壤有机碳和无机碳含量的空间变异也具有重要影响:降雨量每增加1 mm,表层(0~20 cm)土壤有机碳含量增加0.4 g kg-1,而淀积层(40~80 cm)土壤无机碳含量下降0.2 g kg-1;植被类型在一定程度上影响了土壤有机碳的富集程度。本研究揭示了青藏高寒山区土壤碳循环及其碳库预测应充分考虑微地形对坡面尺度下土壤碳垂直分布、碳库组成和空间变异的影响。     

华北平原大气降水对土壤淋洗脱盐的影响

华北平原属季节性干旱半湿润太平洋季风气候区,降水量500-600 mm,年际和年内降水分布不均,旱涝盐碱灾害并存,成为农业生产可持续发展的主要制约因素。降水量74%集中在雨季,对土壤发生淋洗脱盐作用。一般在雨季7-8月份降水量超过300 mm,土体表现为脱盐。次降水量超过25 mm,根层土壤发生淋洗脱盐。海河平原自1964年逐年开挖骨干排水河道,使海河五大河流水系都有了自己的入海尾闾, 在排洪排涝的同时也排走了大量的盐分。20世纪60年代末,开始大规模开发利用地下水,井灌的同时降低了地下水位,起到井排作用,减少了潜水蒸发,增大了降雨入渗,加强了降雨淋洗脱盐作用,并引河水回灌补源,淡化了地下水。华北平原控制了灌区土壤次生盐碱化,而且大面积盐碱地得到改良。