Soil organic carbon sequestration as affected by tillage, crop residue, and nitrogen application in rice–wheat rotation system

Despite being a major domain of global food supply, rice?Cwheat cropping system is questioned for its contribution to carbon flux. Enhancing the organic carbon pool in this system is therefore necessary to reduce environmental degradation and maintain agricultural productivity. A field experiment (November 2002?CMarch 2006) evaluated the effects of soil management practices such as tillage, crop residue, and timing of nitrogen (N) application on soil organic carbon (SOC) sequestration in the lowland of Chitwan Valley of Nepal. Rice (Oryza sativa L.) and wheat (Triticum aestivum L.) were grown in rotation adding 12?Mg?ha^?1?y^?1 of field-dried residue. Mung-bean (Vigna radiata L.) was grown as a cover crop between the wheat and the rice. Timing of N application based on leaf color chart method was compared with recommended method of N application. At the end of the experiment SOC sequestration was quantified for five depths within 50?cm of soil profile. The difference in SOC sequestration between methods of N application was not apparent. However, soils sequestered significantly higher amount of SOC in the whole profile (0?C50?cm soil depth) with more pronounced effect seen at 0?C15?cm soil depth under no-tillage as compared with the SOC under conventional tillage. Crop residues added to no-tillage soils outperformed other treatment interactions. It is concluded that a rice?Cwheat system would serve as a greater sink of organic carbon with residue application under no-tillage system than with or without residue application when compared to the conventional tillage system in this condition.     

Morphological and physiological characters affecting flower drop and fruit set of tomatoes at high temperatures

Summary Seven tomato cultivars and lines were studied under high temperature conditions. Fruit set varied between 77.3% in the heat tolerant cv. Hotset, 62% in cv. Gamad and 16.3% in the most sensitive cv. Hosen-Eilon. The characters contributing to low fruit set were bud drop, splitting of the antheridial cone, style exsertion and reduction of the quantity and/or functionality of the gametes. Employing the above characters as criteria for selection, fruit set of an F₄ line, phenotypically similar to the sensitive parent, was improved to 63.1%. Improved fruit set, 87.6%, was also obtained in an F₁ hybrid between Hotset and Gamad. The importance is discussed of various easily recognizable flower components contributing to satisfactory fruit set under high temperatures and their possible use in breeding is elaborated.     

Genetic structure of Phaeosphaeria nodorum populations in the north-central and midwestern United States

Stagonospora nodorum blotch, caused by Phaeosphaeria nodorum, is considered one of the most destructive foliar diseases of wheat in the United States. However, relatively little is known about the population biology of this fungus in the major wheat-growing regions of the central United States. To rectify this situation, 308 single-spore isolates of P. nodorum were analyzed from 12 populations, five from hard red spring wheat cultivars in Minnesota and North Dakota and seven from soft red winter wheat in Indiana and Ohio. The genetic structure of the sampled populations was determined by analyzing polymorphisms at five microsatellite or simple-sequence repeat (SSR) loci and the mating type locus. Although a few clones were identified, most P. nodorum populations had high levels of gene (H(S) = 0.175 to 0.519) and genotype (D = 0.600 to 0.972) diversity. Gene diversity was higher among isolates collected from spring wheat cultivars in North Dakota and Minnesota (mean H(S) = 0.503) than in those from winter wheat cultivars in Indiana and Ohio (H(S) = 0.269). Analyses of clone-corrected data sets showed equal frequencies of both mating types in both regional and local populations, indicating that sexual recombination may occur regularly. However, significant gametic disequilibrium occurred in three of the four populations from North Dakota, and there was genetic differentiation both within and among locations. Genetic differentiation between the hard red spring and soft red winter wheat production regions was moderate (F(ST) = 0.168), but whether this is due to differences in wheat production or to geographical variation cannot be determined. These results suggest that sexual reproduction occurs in P. nodorum populations in the major wheat-growing regions of the central United States, and that geographically separated populations can be genetically differentiated, reflecting either restrictions on gene flow or selection.     

Policosanol content and composition in perilla seeds

Policosanols, long-chain alcohols, have many beneficial physiological activities. Contents and compositions in perilla seeds (Perilla frutescens) produced in Korea and China were determined. Waxy materials were extracted from perilla seeds using hot hexane. Yield of the waxy materials from perilla seeds was 72.1 mg/100 g of dry weight. Contents and compositions of the waxy materials and policosanols were identified and quantified by TLC, HPLC, and GC. Major components of the waxy materials from Korean and Chinese perilla seeds were policosanols (25.5 and 34.8%, respectively), hydrocarbons (18.8 and 10.5%), wax esters, steryl esters and aldehydes (53.0 and 49.8%), acids (1.7 and 2.1%), and triacylglycerols (1.0 and 2.9%), determined by HPLC. For comparison, waxy materials of sesame seeds were also analyzed. Yield of the waxy materials from sesame seeds were 8.6 mg/100 g. Less than 5% policosanols were detected in the waxy materials extracted from sesame seeds produced in Korea and China. Wax esters or steryl esters accounted for 93-95% of the sesame waxy materials. Policosanols in the perilla seeds were composed of 67-68% octacosanol, 16-17% hexacosanol, 6-9% triacontanol, and others.     

Characterization of Zinc Oxide Nano Particles and Their Effect on Growth of Maize (Zea mays L.) Plant

In the current literature, the impact of nano-particles (NPs) on growth of higher plants has scantly been reported. An investigation was carried out to study the effect of zinc oxide nano-particles (<100 nm) on growth of maize (Zea mays L.) plant, as one of the major agricultural crops, in a solution culture system. Various concentrations of zinc (Zn) were applied through nano-zinc oxide (ZnO) particles (<100 nm) in suspension form and in ionic form through zinc sulfate (ZnSO₄) salt in Hoagland solution culture. Experimental results showed that nano zinc oxide particles could enhance and maintain the growth of maize plant as well as conventional Zn fertilizer (as ZnSO₄). The plant parameters like plant height, root length, root volume, and dry matter weight were all improved due to application of zinc oxide nano-particle. These findings indicate that plant roots might have the unique mechanism of assimilating nano-Zn and using for its growth and development. Different enzymatic activities were also studied and experimental results revealed that nano-ZnO particles (<100 nm) also governed the enzymatic activity of maize plant. A separate laboratory experiment was also carried out to characterize the zinc oxide nano particle for its size, zeta potential, etc.     

Effects of temperature on infection and subsequent development of clubroot under controlled conditions

Controlled‐environment studies were conducted on two Brassica crops (canola, Brassica napus; and Shanghai pak choi, B. rapa subsp. chinensis var. communis) to examine the effects of temperature on infection and subsequent development of clubroot caused by Plasmodiophora brassicae. In the first experiment, canola seedlings were grown in infested soil for 3 weeks at 14–26°C to assess the impact on primary and secondary infection and transferred to 20°C for 3 weeks to assess symptom development under uniform conditions, or started at 20°C for 3 weeks and then placed at the treatment temperatures for the final 3 weeks to assess the impact of temperature on symptom development. A second experiment examined a wider range of temperatures (10–30°C). Similar experiments were also conducted on Shanghai pak choi. The studies demonstrated that clubroot severity was affected by temperature during both infection and vegetative development of the crop. Both early and late in crop development, little or no clubroot developed at temperatures at or below 17°C, and development was slower above 26°C than at 23–26°C for both crops throughout the study. In canola, the high levels of inoculum used in the study resulted in a high incidence of clubroot irrespective of temperature, but in pak choi incidence showed the same pattern as severity. This is the first study to demonstrate under controlled conditions that temperature during vegetative growth of the crop affects symptom development of clubroot.     

In vitro germination and viability of buckwheat (Fagopyrum esculentum Moench) pollen

An in vitro method for the germination of common buckwheat pollen was developed. Pollen grains were successfully germinated in an artificial medium consisting of 0.2 g each of MnSO₄, Ca(NO₃)2.4H₂O and KNO₃, 0.04 g H₃BO₃, 15 g sucrose and 30 g polyethylene glycol (molecular weight approximately 20,000) dissolved in 100 ml of double distilled water. The viability of pollen was assessed by in vivo and in vitro germination tests at 20 °C and 25 °C over a 38 h time period. Pollen grains were collected and germinated at 4 h intervals from freshly harvested flowers grown under 16 h day length and a constant temperature. Maximum pollen viability was found 2 h and 6 h after first light when plants were maintained at 25 °C and 20 °C, respectively. Viability, as measured by germination percentage, was similar at both temperature regimes. Some pollen remained viable for approximately 34 to 38 h in intact flowers, but all pollen lost viability in less than an hour when stored at room temperature without humidity control. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mayweed chamomile (Anthemis cotula L.) biology and management—A review of an emerging global invader

The globally invasive weed, mayweed chamomile (Anthemis cotula L.) is an annual, bushy, ill-scented herb, originating in Eurasia. It is aggressively weedy in croplands, field-side ditches, wet areas and along roadsides, especially in slightly acidic, nitrogen-rich, clay-loam soils. In addition to interfering with crop growth, the weed causes dermatitis and eye irritation in humans, skin rashes and sour mouth in domesticated mammals, and off-flavours in cow's milk through forage contamination. Although A. cotula may be managed effectively with some broadleaf herbicides in cereal crops, it is much more difficult to manage in broadleaved crops and cover crops. In some regions, aggressive use of relatively few herbicides has selected for acetolactate synthase herbicide resistance in A. cotula. Therefore, A. cotula poses serious ecological and economic challenges in many regions. Despite this threat, the details of A. cotula biology and ecology in the context of environmental change remain relatively unknown. For example, the reason for the invasiveness of A. cotula remains uncertain, but is presumed to be due to abundant seed production, allelochemicals, mycorrhizal associations, minimal herbivory in invaded ranges, ability to attract generalist pollinators through an extended flowering period and adaptive capacity in a wide range of soil types and conditions. In this paper, we comprehensively review the literature and ongoing work on A. cotula and provide a research agenda to improve understanding and management of this species.     

Evaluating smallholder farmers’ demand for rice variety attributes in Nepal

Despite the release of many modern varieties of rice (Oryza sativa), farmers in Nepal have been cultivating relatively few rice varieties. The objective of this study is to estimate farmers’ demand for rice variety attributes and to identify the factors that influence their decision regarding varietal choice. Yield increase is considered jointly with other attributes, such as cooking and eating quality, drought tolerance, and maturity period. Choice experiments were conducted and results showed that there was significant demand from farming households for yield increase, improvement in cooking and eating quality, tolerant to drought, and short maturing varieties. The choice data were analyzed using a multinomial and random parameter logit model. From a policy perspective, results showed that for broader adoption of crop varieties, variety development programs should give priority to aforementioned attributes rather than solely on increased crop productivity.