Effects of EC-based irrigation scheduling and CO2 enrichment on water use efficiency of a greenhouse cucumber crop

An EC-based irrigation strategy was tested in two greenhouse soilless cucumber crops grown under the autumn-winter conditions of the Mediterranean area. One of the crops was subjected to CO₂ enrichment using a dynamic control strategy, while the other one was not enriched. Fresh yield of the CO₂-enriched crop was 19% higher than of the non-enriched one, while crop water uptake was not significantly different between the two treatments, implying that the corresponding increase in water use efficiency, calculated on the basis of crop water uptake, was through increased growth and yield, not through reduction in water uptake and transpiration. The overall water use efficiency, based on the amount of applied water, was found to be about 40% higher in the CO₂-enriched greenhouse due to the combined effect of (i) the greater biomass production for the same amount of transpired water and (ii) the lower leaching fraction in the enriched crop compared with the reference one. The latter effect could be ascribed to the higher mineral acquisition of the enriched crop. It is concluded that CO₂ enrichment combined to an EC-based irrigation scheduling lead to synergistic beneficial effects on the overall water use efficiency of soilless greenhouse cropping systems and to a drastic reduction of the leaching fraction.     

Effect of irrigation water salinity on transpiration and on leaching requirements: A case study for bell peppers

Maximization of crop yields when the salinity of irrigation water is high depends on providing plant transpiration needs and evaporative losses, as well as on maintaining minimum soil solution salinity through leaching. The effect of the amount of applied irrigation water was studied regarding transpiration, yields, and leaching fractions as a function of irrigation water salinity. Bell pepper (Capsicum annum L. vars. Celica and 7187) in protected growing environments in the Arava Valley of Israel was used as a case study crop to analyze water quantity–salinity interactions in a series of lysimeter, field and model simulation experiments. Leaching fraction was found to be highly influenced by plant feedback, as transpiration depended on root zone salinity. Increased application of saline irrigation water led to increased transpiration and yields. The higher the salinity level, the greater the relative benefit from increased leaching. The extent of leaching needed to maximize yields when irrigating with saline water may make such practice highly unsustainable.     

渗育性水稻土渗滤液中的磷组分研究

本试验在太湖地区长江岸边砂质渗育性(漏水型)水稻土上进行,研究在麦稻轮作条件下连续两年施用不同磷肥(每季P 0、30、70、150和300 kg hm-2),稻季各层次土壤溶液中(30、60和90 cm)磷的组分,以探讨磷素在剖面中垂直纵向移动的规律。结果表明:施肥处理在施肥初期提高了30 cm处土壤溶液中溶解磷浓度,对60 cm处溶解磷浓度影响不大,对90 cm处溶解磷浓度没有影响。各处理60 cm和90 cm处土壤溶液中溶解磷的浓度几乎全部超过水体富营养化磷的阈值,故在研究该地区水体富营养化时,要注意渗漏磷排放可能的贡献。特别应指出的是,除6月13日对照处理外,各处理90 cm处土壤溶液中的磷均以溶解有机磷为主,占总溶解磷的56%~100%,表明有机磷(外源加入或内源残留的)比无机磷对环境的潜在威胁将更大。     

Response of the N and P cycles of an old-growth montane forest in Ecuador to experimental low-level N and P amendments

Atmospheric nitrogen (N) and phosphorus (P) depositions are expected to increase in the tropics as a consequence of increasing human activities in the next decades. In the literature, it is frequently assumed that tropical montane forests are N-limited, while tropical lowland forests are P-limited. In a low-level N and P addition experiment, we determined the short-term response of N and P cycles in a north Andean montane forest on Palaeozoic shists and metasandstones at an elevation of 2100 m a.s.l. to increased N and P inputs. We evaluated experimental N, P and N + P additions (50 kg ha⁻¹ yr⁻¹ of N, 10 kg ha⁻¹ yr⁻¹ of P and 50 kg + 10 kg ha⁻¹ yr⁻¹ of N and P, respectively) and an untreated control in a fourfold replicated randomized block design. We collected litter leachate, mineral soil solution (0.15 and 0.30 m depths), throughfall and litterfall before the treatment began (August 2007) until 16 months after the first nutrient application (April 2009). Less than 10 and 1% of the applied N and P, respectively, leached below the organic layer which contained almost all roots and no significant leaching losses of N and P occurred to below 0.15 m mineral soil depth. Deposited N and P from the atmosphere in dry and wet form were retained in the canopy of the control treatment using a canopy budget model. Nitrogen and P retention by the canopy were reduced and N and P fluxes in throughfall and litterfall increased in their respective treatments. The increase in N and P fluxes in throughfall after fertilization was equivalent to 2.5% of the applied N and 2% of the applied P. The fluxes of N and P in litterfall were up to 15% and 3%, respectively, higher in the N and N + P than in the control treatments. We conclude that the expected elevated N and P deposition in the tropics will be retained in the ecosystem, at least in the short term and hence, N and P concentrations in stream water will not increase. Our results suggest that in the studied tropical montane forest ecosystem on Palaeozoic bedrock, N and P are co-limiting the growth of organisms in the canopy and organic layer.     

Fertilization Experiments on Forest Mineral Soils: A Review of the Norwegian Results

The paper gives a brief overview of the background, history and main results of forest fertilization experiments on mineral soils in Norway. Positive results of initial phosphorus (P) fertilization on survival and growth of Norway and Sitka spruce have only been achieved in the coastal districts of western Norway. Other elements have seldom given any significant effect. In young and old stands of Norway spruce and Scots pine nitrogen (N) fertilization with 150 kg N ha -1 usually gave increment increases in the range of 1-2 m 3 ha -1 yr -1 , for a period of 6-8 yrs after application. Given individually, no other element has proved stimulating to stem growth in a similar way. In young Norway spruce stands P has often given additional growth response when given together with N. Liming has been shown to have no or negative effects on tree growth. Fertilization experiments have changed from being management orientated towards addressing the problems of possible nutrient imbalances.     

水肥状况对土壤剖面中锰的移动和水稻吸锰的影响

水旱轮作条件下水麦缺锰是四川冲积性水稻土上主要的养分胁迫问题,为了深入探讨这一问题,作者利用模拟土柱试验研究了不同水肥状况对四川两种典型冲积土中锰的迁移,转化及其对水稻吸锰的影响。     

一种耐盐型保水剂对沙培玉米生长特性的影响

干旱与肥料利用率较低已成为制约我国农业发展的重要因素。以沙子代替土壤,通过加入自制耐盐保水剂(Salt-tolerant water detaining polymer, SWDP),进行钾肥淋溶和连续两茬玉米盆栽试验。盆栽试验按SWDP投加量设置4个处理,即SWDP投加量分别为0(空白)、0.5、1.0和1.5g·kg~(-1)沙子。结果表明,SWDP的加入有利于降低沙子中钾肥的淋溶损失,不同处理(SWDP投加量分别为0.5和1.0 g·kg~(-1)沙子)钾肥淋溶累积损失量较空白分别降低了12.69%和47.85%;不同处理干旱缺水组玉米植株的存活时间较空白分别延长了12、19和30 d;正常供水组,第一茬不同处理玉米植株氮素吸收量较空白分别增加了8.83%、19.63%和22.39%,磷素吸收量分别增加了29.31%、30.19%和52.38%,钾素吸收量分别增加了11.61%、18.12%和20.27%;第二茬不同处理玉米植株氮素吸收量较空白分别增加了55.50%、117.1%和143.7%,磷素吸收量分别增加了77.12%、161.3%和156.5%,钾素吸收量分别增加了55.42%、74.13%和84.33%。上述结果说明,在干旱甚至沙漠地区施入SWDP能够明显降低土壤养分的流失,提高土壤含水率和植物对土壤养分的利用效果。     

Assessment of tillage strategies to decrease nitrate leaching in the Brimstone Farm Experiment, Oxfordshire, UK

Tillage may influence nitrate losses from agricultural soils. Losses of nitrate were measured in drainflow at 60 cm depth and in combined surface runoff and interflow in the A horizon (=surface layer flow) on hydrologically sealed plots with a two-year comparison (1988–1990) of shallow-tine cultivation vs. mouldboard ploughing. Ploughing increased concentrations and loadings of nitrate in drainflow and surface layer flow, especially in the first year. After these two years the shallow-tined plots were ploughed to plant winter beans (Vicia faba L.), and nitrate in drainflow then increased over the next three winters, slightly exceeding that from the plots which had been ploughed throughout for winter cereals. The composition of the surface layer flow did not show this effect, however. Calculations of net winter mineralisation of soil organic nitrogen showed that shallow-tine cultivation may have decreased mineralisation slightly compared with ploughing in the first two years. These calculations did not indicate any increase in mineralisation for two winters after the minimally cultivated plots were ploughed in autumn 1990, probably because the soil was then very dry. This increase was apparently delayed until the fifth winter (1992/1993), which was much wetter than any since autumn 1990. In the previous eight years (1980–1988) half of the plots had been ploughed and half had been direct drilled. Averaged over the five winters 1988/1989–1992/1993, the five measures of nitrate loss in drainflow from plots previously direct drilled were 6–57% more than from plots previously ploughed, and winter mineralisation was 20% more, with no evidence of any decline in either with time. The nitrate produced by mineralisation of organic matter conserved by the eight years of direct drilling was mainly lost by leaching or denitrification; it was of little or no benefit to the crops. The results suggest that in the long term more nitrate is leached from land subject to periods of minimal or zero tillage and ploughing than from land ploughed every year.     

不同土壤淋洗方式下有机—无机复合材料胶结包膜肥料钾素溶出速率比较

应用由水基成膜法研制的4种有机-无机复合材料胶结包膜肥料(B2、PS、F2、F2F)进行土柱淋洗试验,研究其在不同土壤类型条件下的钾素溶出规律。结果表明:4种胶结包膜肥料在48d内钾素累积溶出率为44.02%(红壤)>34.59%(褐土)>25.92%(黑土)。同一种胶结包膜肥料在红壤、褐土和黑土中的钾素瞬时溶出率峰值出现时间一致(以B2为例);钾素溶出峰值之前,瞬时溶出率在2~13 d内为红壤>褐土>黑土,钾素峰值溶出率为10.39%(红壤)>7.09%(褐土)>5.99%(黑土),而峰值过后,三土壤间瞬时溶出率差异不显著(P>0.05)。说明包膜肥料本身释放钾素的速率受不同质地的土壤影响较小,但其淋出量受土壤影响较大。     

雨季白洋淀地区散养鸭粪中氮素去向研究

散养是白洋淀地区养鸭的主要方式,散养过程中产生的大量鸭粪因不够集中、难以收集而残留于土壤表面。借助小区模拟试验,研究了白洋淀雨季(6～9月份)残留在土壤表面的鸭粪中氮素动态变化及环境影响因素。结果表明:鸭粪中部分氮素以NH3的形式挥发,挥发期为45d左右,挥发量约为8.72kg·hm-2;NH3挥发主要集中在鸭粪排出后的7d内,挥发初期随温度降低、湿度增加和光照减弱逐渐降低,随着挥发的减弱其与环境因素相关性不明显。模拟小区地表径流中总氮(TN)流失负荷为10.05kg·hm-2,以颗粒态氮(PN)为主;可溶态氮(TDN)中,以无机氮为主。淋溶水中总氮淋失负荷为19.30kg·hm-2,以NO3--N为主。自然状态下,鸭粪中约10%氮素以NH3挥发、地表径流和淋溶流失;部分氮素残留于土壤中,另有部分未矿化鸭粪存在于土壤表面,约占鸭粪总量的45.09%。残留于土壤中的氮素一旦达到土壤临界值,将威胁当地水环境安全,因此必须采取有效措施,防止养鸭带来的过量氮素累积造成的环境污染。