减施氮肥对稻田土壤剖面养分分布特征的影响

为探讨减施氮肥对养分在剖面垂直的分布与迁移的影响,采用大田试验,探讨了减施氮肥对稻田剖面养分累积和分布的影响.结果表明:3个处理下土壤剖面养分累积的趋势是:有机质、全氮、全磷、碱解氮、速效磷含量随土层深度的增加而降低,而全钾及速效钾含量则随土层深度的增加而提高.T3(80％的习惯施氮量)处理中除耕层的有效氮、速效磷及速效钾含量较T2(习惯施氮量)处理降低外,土壤其它各层有机质、全氮、全磷、全钾、有效氮、速效磷以及速效钾含量均较T2处理有所增加.T3处理有机质的增加主要集中在0～60 cm土层中,氮素主要集中在0～40 cm土层中,钾素则主要集中在0～20 cm土层中,土壤中各层的磷素在两个施肥处理中无显著差异,说明T3处理增加的养分主要集中在作物能吸收的范围内,这意味着对土壤培肥和作物生产更有利.     

不同氮磷钾处理对中浙优1号水稻产量、品质、养分吸收利用及经济效益的影响

采用"3414"试验设计,在2008-2010年3年中研究了不同氮磷钾施肥处理对浙中水稻籽粒产量、品质、养分吸收利用及经济效益的影响。结果表明,氮、磷、钾肥的施用可以显著提高籽粒产量,且3种肥料配施的增产效果显著优于任意两种肥料配施;其对籽粒产量的作用顺序为NKP。N3P2K2处理产量最高,为8746kg/hm2。施氮可提高稻米胶稠度、蛋白质含量和总氨基酸含量,降低碱消值;施磷可提高蛋白质含量;施钾可提高胶稠度、碱消值及蛋白质含量;氮、磷、钾肥的施用对直链淀粉含量均无显著影响。水稻养分总吸收量和100kg籽粒养分需求量随施肥量增加而增加,肥料吸收利用率及农学利用率则随施肥量增加而下降。氮、磷、钾肥吸收利用率分别为25.2%、38.3%和36.0%。N2P2K2、N2P3K2、N2P2K1和N3P2K2处理的经济效益较高,比N0P0K0处理分别提高21.1%、20.3%、20.3%和22.4%,差异达显著水平。利用肥料效应方程,得出该地区获得最高产量的氮、磷(P2O5)和钾(K2O)肥施用量分别为258.8kg/hm2、39.3kg/hm2和100.8kg/hm2。     

不同土壤养分状况下氮钾配施对弱筋小麦产量和品质的影响

为了给弱筋小麦高产优质栽培提供依据,在两种不同养分状况的土壤(土壤Ⅰ和Ⅱ)上,研究了氮钾配施对弱筋小麦产量和品质的调控效应.结果表明,合理配施氮钾肥能够显著地提高弱筋小麦产量.在土壤Ⅰ上,处理N180K150(施氮和施钾量分别为180和105 kg/ha)获得最高产量5 023 kg/ha;在土壤Ⅱ上,处理N180K90(施氮和施钾分别为180和90 kg/ha)获得最高产量5 145 kg/ha.在两种土壤上,氮肥对产量的效应均大于钾肥效应,在土壤Ⅰ上氮钾对小麦产量表现出极显著的正向交互作用.两种土壤上,增施氮肥均显著降低了弱筋小麦的专用品质,而在速效钾含量较高的土壤Ⅱ上,配施钾肥有利于提高弱筋小麦的品质.氮钾肥配施对弱筋小麦淀粉糊化特性无明显影响.土壤基础肥力对弱筋小麦的品质有明显的影响.本试验条件下,在有机质含量和氮素含量较低的土壤Ⅱ上种植弱筋小麦,并适当降低氮肥用量有利于改善弱筋小麦品质.     

不同品种玉米对蔬菜大棚土壤次生盐渍化的改良效应

为了解玉米对蔬菜大棚土壤次生盐渍化的改良效应,以‘鲜玉糯2号’、‘泰系2号’、‘泰系3号’、‘伯洪5号’和‘美兰16号’5种玉米为研究对象,对其养分积累情况、不同土层养分和次生盐渍化的变化情况进行研究。结果表明：（1）‘鲜玉糯2号’的总生物量、吸氮量、吸磷量、吸钙量和吸镁量最高,分别为714.94、12.30、2.70、6.11、1.13 kg/667 m ²;（2）与不种植任何填闲作物的对照相比,各品种玉米对土壤0~20 cm的碱解氮、速效磷、速效钾、交换性钙和交换性镁含量均有一定的消减作用,其中‘鲜玉糯2号’对碱解氮、速效磷、交换性钙和交换性镁含量消减能力最佳;（3）种植玉米使土壤0~20 cm的电导率下降15.18%~35.43%,其中‘鲜玉糯2号’下降幅度最大。蔬菜大棚在休闲期种植玉米,能有效降低养分的积累,缓解土壤次生盐渍化。     

论钾肥对水稻的增产效果

土壤自从被耕种以来,产量就成为农业生产的社会目的,产量越高,从土壤中摄取的物质就越多。如不及时补给,土壤中有机质就会逐年减少,导致土壤肥力不断降低,地力消耗越来越大。加之,近年来水稻生产不断发展,单位面积产量不断提高,以及氮、磷、钾化肥又来不及补充的情况下,使土壤中原有的速效钾逐年被农作物带走,而通过施农肥补充速效钾远不够农作物需要,以致造成土壤中氮、磷、钾比例严重失调,为此造成病虫害蔓延,水稻品质下降。所以,为使作物提高抗逆性,提高产量,就必须增施钾肥达到养分平衡,满足作物生长发育的需要。1　土壤磷、钾含量的变…     

不同茬口对小麦养分利用和产量的影响

为了探究不同茬口对小麦生产的影响,在测定玉米、大豆、花生、甘薯4种不同作物收获后土壤养分状况的基础上,对不同茬口下小麦植株养分吸收、利用和产量进行了研究。结果表明,与玉米茬相比,大豆茬的土壤速效磷含量降低,土壤速效氮和速效钾含量提高,花生茬的土壤速效氮和速效磷含量提高,甘薯茬的土壤速效氮和速效钾含量下降;大豆、花生和甘薯茬有利于小麦植株养分的积累,并能显著提高千粒重,但甘薯茬的小麦产量显著低于玉米茬。因此,大豆和花生可作为冬小麦种植区两熟复种模式的适宜前茬作物。     

胡椒园间作槟榔对胡椒产量及养分利用的影响

胡椒园间作槟榔是海南胡椒间作体系中应用较广的一种模式,为探明其间作优势来源,以海南胡椒优势种植区4个试验点的胡椒单作与胡椒/槟榔模式为研究对象,调查了2009~2011年各点胡椒产量与养分投入状况,测定2011年土壤养分与胡椒植株叶片养分含量,从而对比了间作模式与胡椒单作模式下胡椒产量、土壤养分状况、肥料产量贡献率和胡椒叶片养分含量的差异。结果表明：在各试验点不同产量水平下,同一地点间作模式的胡椒产量均极显著高于单作。间作模式土壤氮、磷、钾全量含量略低于单作,但未达到显著水平;间作模式土壤速效磷和速效钾含量高于单作,且速效磷差异达到显著水平。在养分投入相同的条件下,间作模式氮、磷、钾肥料偏生产力均极显著高于单作。间作模式下胡椒叶片磷、钾养分含量周年大于单作。上述结果表明胡椒/槟榔间作提高了土壤中速效养分的含量,促进了胡椒对磷、钾等养分的吸收,从而提高了其肥料利用效率,并最终提高胡椒产量。胡椒/槟榔的间作优势可能与二者地下部互作有关。     

钾肥对油菜植株养分及种子产量品质的影响

本文通过马肝泥水稻长期定位施肥试验及灰潮土复混肥田间试验表明:速效磷钾含量较低的马肝泥水稻土,施钾肥显著促进油菜植株N、P、K养分与干物质积累,提高根、茎、角壳含K量(籽粒含K较稳定),增加角果数;与氮磷配合施钾显著提高油菜籽产量。而土壤速效磷钾中上等的灰潮土,与氮磷配合施钾,籽粒产量虽有增加,但差异不显著,植株N、P、K含量亦无明显变化。钾肥提高菜籽含油量和油酸含量,降低芥酸含量,硫甙含量亦有降低。     

槟榔间作香露兜对土壤养分和养分吸收的影响

为了研究槟榔间作香露兜对土壤养分和养分吸收的影响,采用盆栽试验的方法,对槟榔单作、槟榔间作香露兜和香露兜单作3种种植模式的土壤理化性质和养分吸收进行比较研究。结果表明：槟榔间作香露兜后,相对于单作槟榔,土壤EC值和碱解氮含量显著降低47.15%和25.74%,土壤速效磷含量显著增加32.32%,其中碱解氮与过氧化氢酶和过氧化物酶极显著负相关,速效磷与总根长、根系总表面积、根体积、根数目、脲酶和酸性磷酸酶显著正相关,速效磷与过氧化氢酶和过氧化物酶极显著正相关;槟榔地上部N浓度以及香露兜地上部P和K浓度分别显著增加41.56%、26.56%和25.69%;而槟榔和香露兜根系以及地上部N、P和K养分含量均高于单作,其中根系槟榔P和K含量和香露兜K含量显著增加;同时,间作后槟榔和香露兜对N的吸收效率均高于单作,香露兜的P和K的吸收效率高于单作并略高于槟榔的吸收效率,其中P和K的吸收效率与总根长、总表面积、根体积、根数目均显著正相关,氮的吸收效率与根系形态无显著相关关系。综上所述,槟榔间作香露兜增加了土壤中速效磷含量,促进了槟榔和香露兜对氮、磷和钾养分的吸收,土壤速效磷含量的增加、养分吸收效率的提高均与根系形态显著正相关。     

成龄胶园间作不同禾本科作物对土壤养分与土壤酶的影响

研究成龄胶园条件下间作不同禾本科作物对胶园土壤养分和土壤酶的影响,为成龄胶园禾本科作物间作合理施肥和土壤培肥提供理论依据。本研究以间作3种禾本科作物的胶园为处理,以单作胶园土壤为对照,采用土壤常规分析方法分别测定土壤养分和土壤酶。结果表明：间作的3种禾本科作物对胶园土壤的有机质、全氮、全钾含量、酸性磷酸酶活性、过氧化氢酶活性的影响不显著;显著降低了全磷、速效磷含量、pH值、土壤脲酶活性;显著增加了铵态氮、硝态氮(除坚尼草外)、速效钾及土壤蔗糖酶活性(除旱稻外)。这些结果说明,间作禾本科作物能提高土壤的土壤硝态氮、铵态氮及速效钾含量,短时期内能提高土壤的供氮、供钾能力,但降低了土壤磷含量和土壤磷的供应能力。由此可见,在成龄胶园内进行间作,必须加强间作物施肥,以实现土壤养分收支平衡,维持土壤肥力、提高土壤质量。     

The competitive ability of pea-barley intercrops against weeds and the interactions with crop productivity and soil N availability

Grain legumes, such as peas (Pisum sativum L.), are known to be weak competitors against weeds when grown as the sole crop. In this study, the weed-suppression effect of pea-barley (Hordeum vulgare L.) intercropping compared to the respective sole crops was examined in organic field experiments across Western Europe (i.e., Denmark, the United Kingdom, France, Germany and Italy). Spring pea (P) and barley (B) were sown either as the sole crop, at the recommended plant density (P100 and B100, respectively), or in replacement (P50B50) or additive (P100B50) intercropping designs for three seasons (2003-2005). The weed biomass was three times higher under the pea sole crops than under both the intercrops and barley sole crops at maturity. The inclusion of joint experiments in several countries and various growing conditions showed that intercrops maintain a highly asymmetric competition over weeds, regardless of the particular weed infestation (species and productivity), the crop biomass or the soil nitrogen availability. The intercropping weed suppression was highly resilient, whereas the weed suppression in pea sole crops was lower and more variable. The pea-barley intercrops exhibited high levels of weed suppression, even with a low percentage of barley in the total biomass. Despite a reduced leaf area in the case of a low soil N availability, the barley sole crops and intercrops displayed high weed suppression, probably because of their strong competitive capability to absorb soil N. Higher soil N availabilities entailed increased leaf areas and competitive ability for light, which contributed to the overall competitive ability against weeds for all of the treatments. The contribution of the weeds in the total dry matter and soil N acquisition was higher in the pea sole crop than in the other treatments, in spite of the higher leaf areas in the pea crops.     

Effects of crop density and tillage system on grain yield and N uptake from soil and atmosphere of sole and intercropped pea and oat

Pea (Pisum sativum L.) and oat (Avena sativa L.) were grown as sole and mixed crops in various densities under two different tillage systems on a loess soil near Göttingen/Germany in a 2-year field experiment (2002/2003). In the conventional tillage system a mouldboard plough (CT) was used and in the minimum tillage system a rotary harrow (MT) was employed. The effect of crop density and tillage system on the grain dry matter and grain N yields, N₂ fixation and soil N uptake were determined to address the following questions: (i) which mixture compositions exhibit the highest grain yields compared to the sole crops, (ii) which mixture compositions also fix a high level of N₂ and leave low levels of residual inorganic soil N after harvest, and (iii) whether the intercrop advantage is influenced by the tillage system. For (i) the result in 2002 showed that the highest grain yields of both sole cropped pea and oat and intercropped pea and oat were achieved at the highest densities. In 2003, when the inorganic soil N content was higher and weather conditions were warmer and drier, grain yields were significantly higher than in 2002, but sole as well as intercropped pea and oat gave their highest grain yields at lower densities. For both years and tillage systems, the highest intercrop advantages were achieved in mixtures with densities above the optimal sole crop densities. The result for (ii) was that a distinctly higher proportion of nitrogen was derived from the atmosphere (Ndfa) by intercropped pea than by sole cropped pea. However, the uptake of soil N by intercropped pea and oat was not reduced in comparison with that of sole cropped oat as the decrease in the uptake of N from the soil by oat at lower oat densities in the mixture was compensated for by the soil N uptake of pea. Additionally, the N_min-N content of the soil following the mixtures and sole cropped oat did not differ, especially in the deeper soil layers because oat in mixture was forced to take up more soil N from deeper layers. Therefore, the risk of soil N losses through leaching after mixtures was lower compared to sole cropped pea. The tillage system (iii) had no significant influence on grain yield and soil N uptake, but N₂ fixation and the competitive ability of intercropped pea were higher under CT than with MT. An additional result was that intercropping led to a significantly increased grain N content of both pea and oat compared to the sole crops. The increase in grain N content from sole to intercrop was from 3.30 to 3.42% for pea and from 1.73 to 1.96% for oat as a mean for both years and tillage systems. The present study confirms that growing pea and oat as intercrops highlights potential economic and environmental benefits which still need to be understood in more detail in order to exploit intercropping to a greater extent.     

The value of catch crops and organic manures for spring barley in organic arable farming

The effect of nitrogen (N) supply and weeds on grain yield of spring barley was investigated from 1997 to 2004 in an organic farming crop rotation experiment in Denmark on three different soil types varying from coarse sand to sandy loam. Two experimental factors were included in the experiment in a factorial design: (1) catch crop (with and without), and (2) manure (with and without). The crop rotation included grass-clover as a green manure crop. Animal manure was applied as slurry in rates corresponding to 40% of the N demand of the cereal crops.

Application of 50 kg NH₄-N ha⁻¹ in manure (slurry) increased average barley grain DM yield by 1.0–1.3 Mg DM ha⁻¹, whereas the use of catch crops (primarily perennial ryegrass) increased grain DM yield by 0.2–0.4 Mg DM ha⁻¹ with the smallest effect on the loamy sand and sandy loam soils and the greatest effect on the coarse sandy soil. Model estimations showed that the average yield reduction from weeds varied from 0.2 to 0.4 Mg DM ha⁻¹ depending on weed species and density. The yield effects of N supply were more predictable and less variable than the effects of weed infestation. The infestation level of leaf diseases was low and not a significant source of yield variation.

The apparent recovery efficiency of N in grains (N use efficiency, NUE) from NH₄-N in applied manure varied from 29 to 38%. The NUE of above-ground N in catch crops sampled in November prior to the spring barley varied from 16 to 52% with the largest value on the coarse sandy soil and the smallest value on the sandy loam soil. A comparison of grain yield levels obtained at the different locations with changes in soil organic matter indicated a NUE of 21–26% for soil N mineralisation, which is smaller than that for the mineral N applied in manure. However, this estimate is uncertain and further studies are needed to quantify differences in NUE from various sources of N.

The proportion of perennial weeds in total biomass increased during the experiment, particularly in treatments without manure application. The results show that manure application is a key factor in maintaining good crop yields in arable organic farming on sandy soils, and in securing crops that are sufficiently competitive against perennial weeds.     

Sitona lineatus (Coleoptera: Curculionidae) Larval Feeding on Pisum sativum L. Affects Soil and Plant Nitrogen

Adults of Sitona lineatus (pea leaf weevil, PLW) feed on foliage of several Fabaceae species but larvae prefer to feed on nodules of Pisum sativum L. and Vicia faba L. Indirectly, through their feeding on rhizobia, weevils can reduce soil and plant available nitrogen (N). However, initial soil N can reduce nodulation and damage by the weevil and reduce control requirements. Understanding these interactions is necessary to make integrated pest management recommendations for PLW. We conducted a greenhouse study to quantify nodulation, soil and plant N content, and nodule damage by weevil larvae in relation to soil N amendment with urea, thiamethoxam insecticide seed coating and crop stage. PLWs reduced the number of older tumescent (multilobed) nodules and thiamethoxam addition increased them regardless of other factors. Nitrogen amendment significantly increased soil available N (>99% nitrate) as expected and PLW presence was associated with significantly lower levels of soil N. PLW decreased plant N content at early flower and thiamethoxam increased it, particularly at late flower. The study illustrated the complexity of interactions that determine insect herbivory effects on plant and soil nutrition for invertebrates that feed on N-fixing root nodules. We conclude that effects of PLW on nodulation and subsequent effects on plant nitrogen are more pronounced during the early growth stages of the plant. This suggests the importance of timing of PLW infestation and may explain the lack of yield depression in relation to this pest observed in many field studies. Also, pea crops in soils with high levels of soil N are unlikely to be affected by this herbivore and should not require insecticide inputs.     

Forage Legumes for Sustainable Cropping Systems

SUMMARY

Perennial and annual forage legumes are important components of sustainable cropping systems. Forage legumes are a primary source of forage to supply protein and fiber for livestock rations. They can be grazed, or stored as hay or silage. They contribute biologically fixed N and sustain the soil by reducing erosion and increasing soil organic matter levels. Diversifying cropping systems by including legumes can also reduce weed, insect, and disease incidence. Potential new uses of legumes include phytoremediation of N contaminated sites and capturing N lost from cropping systems. Legumes also have potential use as a feedstock for renewable energy production. Legumes have traditionally been used in rotation with grain crops but more recently have been shown promise as winter cover crops, intercrops with grain crops, and as living mulches. In this review, we discuss traditional and new roles of forage legumes in sustainable cropping systems with examples primarily chosen from northern USA and Canada.     

Clover cover crops under-sown in winter wheat increase yield of subsequent spring barley—Effect of N dose and companion grass

Four two-year field trials, arranged in randomised split-plots, were carried out in southern Sweden with the aim of determining whether reduced N fertiliser dose in winter wheat production with spring under-sown clover cover crops, with or without perennial ryegrass in the seed mixture, would increase the clover biomass and hence the benefits of the cover crops in terms of the effect on the wheat crop, on a subsequent barley crop and on the risk of N leaching. Four doses of nitrogen (0, 60, 120 or 180 kg N ha⁻¹) constituted the main plots and six cover crop treatments the sub-plots. The cover crop treatments were red clover (Trifolium pratense L.), white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) in pure stands and in mixtures. The winter wheat (Triticum aestivum L.) was harvested in August and the cover crops were ploughed under in November. The risk of N leaching was assessed in November by measuring the content of mineral N in the soil profile (0–30, 30–90 cm). In the following year, the residual effects of the cover crops were investigated in spring barley (Hordeum distichon L.) without additional N. Under-sowing of cover crops did not influence wheat yield, while reduced N fertiliser dose decreased yield and increased the clover content of the cover crops. When N was applied, the mixed cover crops were as effective in depleting soil mineral nitrogen as a pure ryegrass cover crop, while pure clover was less efficient. The clover content at wheat harvest as well as the amount of N incorporated with the cover crops had a positive correlation with barley yield. Spring barley in the unfertilised treatments yielded, on average, 1.9–2.4 Mg DM ha⁻¹ more in treatments with clover cover crops than in the treatment without cover crops. However, this positive effect decreased as the N dose to the preceding wheat crop increased, particularly when the clover was mixed with grass.     

Effect of winter cover crop species and planting methods on maize yield and N availability under irrigated Mediterranean conditions

Under semiarid Mediterranean conditions irrigated maize has been associated to diffuse nitrate pollution of surface and groundwater. Cover crops grown during winter combined with reduced N fertilization to maize could reduce N leaching risks while maintaining maize productivity. A field experiment was conducted testing two different cover crop planting methods (direct seeding versus seeding after conventional tillage operations) and four different cover crops species (barley, oilseed rape, winter rape, and common vetch), and a control (bare soil). The experiment started in November 2006 after a maize crop fertilized with 300 kg N ha⁻¹ and included two complete cover crop-maize rotations. Maize was fertilized with 300 kg N ha⁻¹ at the control treatment, and this amount was reduced to 250 kg N ha⁻¹ in maize after a cover crop. Direct seeding of the cover crops allowed earlier planting dates than seeding after conventional tillage, producing greater cover crop biomass and N uptake of all species in the first year. In the following year, direct seeding did not increase cover crop biomass due to a poorer plant establishment. Barley produced more biomass than the other species but its N concentration was much lower than in the other cover crops, resulting in higher C:N ratio (>26). Cover crops reduced the N leaching risks as soil N content in spring and at maize harvest was reduced compared to the control treatment. Maize yield was reduced by 4 Mg ha⁻¹ after barley in 2007 and by 1 Mg ha⁻¹ after barley and oilseed rape in 2008. The maize yield reduction was due to an N deficiency caused by insufficient N mineralization from the cover crops due to a high C:N ratio (barley) or low biomass N content (oilseed rape) and/or lack of synchronization with maize N uptake. Indirect chlorophyll measurements in maize leaves were useful to detect N deficiency in maize after cover crops. The use of vetch, winter rape and oilseed rape cover crops combined with a reduced N fertilization to maize was efficient for reducing N leaching risks while maintaining maize productivity. However, the reduction of maize yield after barley makes difficult its use as cover crop.     

Characterizing nitrogen use efficiency in natural and agricultural ecosystems to improve the performance of cereal crops in low-input and organic agricultural systems

Low-input and organic farming systems have notable differences in nitrogen (N) sources, cycling and management strategies compared to conventional systems with high inputs of synthetic N fertilizer. In low-input and organic systems, there is greater reliance on complex rotations including annual and perennial crops, organic N sources, and internal N cycling that more closely mimic natural systems. These differences in farming system practices fundamentally affect N availability and N use efficiency (NUE) and could impact crop traits and breeding strategies required to optimize NUE. We assess genetic and environmental factors that could assist breeders in improving crop performance in low-input and organic farming systems by examining NUE in natural and agricultural ecosystems. Crop plants have often been bred for high N productivity, while plants adapted to low N ecosystems often have lower productivity and higher levels of internal N conservation. Breeders can potentially combine N productivity and N conservation through the use of elite and wild germplasm. Beneficial genetic traits include the ability to maintain photosynthesis and N uptake under N stress and the ability to extract soil N at low concentrations, perhaps through beneficial associations with soil microorganisms. In addition, breeding for specific adaptation to climactic and management practices so that crop uptake patterns match N availability patterns, while minimizing pathways of N loss, will be critical to improving NUE.     

Estimation of the N fertiliser requirement of cotton grown after legume crops

In a series of legume-based cropping systems experiments, the economic optimum N fertiliser rate for cotton ranged from 0 to 186 kg N ha⁻¹ depending on the cropping system and soil N fertility. The economic optimum N fertiliser rate was closely correlated with pre-sowing soil nitrate-N (0–30 cm) and petiole nitrate-N (at early flowering). Pre-sowing soil nitrate-N and petiole nitrate-N were also strongly correlated with cotton N uptake at late boll-filling and lint yield of unfertilised cotton.These analyses allow for the estimation of the N fertiliser requirement, providing revised calibrations that more precisely estimate the N-fertiliser requirement of irrigated cotton crops where legume cropping has substantially improved soil N fertility. Such management tools are essential to avoid the problems associated with over- or under-fertilizing cotton crops.The importance of optimising N fertiliser application was demonstrated by examining the effects of crop N nutrition on cotton maturity and fibre quality. Crop maturity (rate of boll opening) was delayed by 1 day for each 83, 16 or 24 kg fertiliser N applied per hectare in the three experiments. Increasing N fertiliser rates generally increased fibre length, and tended to increase fibre strength, whereas micronaire tended to decline.     

Control of damping-off of organic and conventional cucumber with extracts from a plant-associated bacterium rivals a seed treatment pesticide

Environmentally friendly control measures are needed for soilborne diseases of crops grown in organic and conventional production systems. We tested ethanol extracts from cultures of Serratia marcescens N4-5 and N2-4, Burkholderia cepacia BC-1 and BC-2, and Burkholderia ambifaria BC-F for control of damping-off of cucumber caused by the soilborne pathogens Pythium ultimum and Rhizoctonia solani; ethanol being an Organic Materials Review Institute (OMRI) -approved solvent for use in certain applications in organic crop production. Ethanol extracts from strains N4-5 and N2-4 inhibited mycelial growth and germination of sporangia of P. ultimum in vitro but those from strains BC-1, BC-2, BC-F, and the ethanol control did not. Ethanol extracts from strains BC-2 and BC-F inhibited mycelial growth of R. solani in vitro while ethanol extracts from strains BC-1, N2-4, N4-5, and the ethanol control did not. Thin-layer chromatography demonstrated that ethanol extracts from strain N4-5 contained prodigiosin while ethanol extracts from strains BC-2 and BC-F contained pyrrolnitrin; extracts from strains N2-4 and BC-1 did not contain either of these compounds. DNA sequencing confirmed the presence of a biosynthetic gene for prodigiosin in strain N4-5 and its absence in strain N2-4, while a biosynthetic gene for pyrrolnitrin was found in strains BC-2 and BC-F but not in strains N2-4, N4-5, and BC-1. Prodigiosin was previously implicated in inhibition of P. ultimum while pyrrolnitrin has been shown to inhibit R. solani. Certified-organic cucumber seed treated with an ethanol extract of strain N4-5 was the only extract treatment from any of these five microbial strains to effectively suppress damping-off caused by P. ultimum in growth chamber pot experiments. This ethanol extract provided suppression of P. ultimum on cucumber that was similar to that provided by a commercially available seed treatment pesticide and greater than that provided by a commercially available biocontrol agent for this pathogen. The inhibitory factor(s) in ethanol extracts of strain N4-5 was stable as a seed treatment for at least 14 weeks when incubated at 4 °C in the dark. No ethanol extracts applied as treatments of organic cucumber seed consistently suppressed damping-off caused by R. solani in growth chamber pot experiments. Experiments reported here suggest that certain natural products from microbial strains as seed treatments are promising alternatives for control of soilborne diseases in conventional or organic cucumber production systems.