• Authors:
    • Graham, J. H.
    • Wu, T.
    • Chellemi, D. O.
    • Church, G.
  • Source: Phytopathology
  • Volume: 102
  • Issue: 6
  • Year: 2012
  • Summary: Development of sustainable food systems is contingent upon the adoption of land management practices that can mitigate damage from soilborne pests. Five diverse land management practices were studied for their impacts on Fusarium wilt (Fusarium oxysporum f. sp. lycopersici), galling of roots by Meloidogyne spp. and marketable yield of tomato (Solanum lycopersicum) and to identify associations between the severity of pest damage and the corresponding soil microbial community structure. The incidence of Fusarium wilt was >14% when tomato was cultivated following 3 to 4 years of an undisturbed weed fallow or continuous tillage disk fallow rotation and was >4% after 3 to 4 years of bahiagrass (Paspalum notation) rotation or organic production practices that included soil amendments and cover crops. The incidence of Fusarium wilt under conventional tomato production with soil fumigation varied from 2% in 2003 to 15% in 2004. Repeated tomato cultivation increased Fusarium wilt by 20% or more except when tomato was grown using organic practices, where disease remained less than 3%. The percent of tomato roots with galls from Meloidogyne spp. ranged from 18 to 82% in soil previously subjected to a weed fallow rotation and 7 to 15% in soil managed previously as a bahiagrass pasture. Repeated tomato cultivation increased the severity of root galling in plots previously subjected to a conventional or disk fallow rotation but not in plots managed using organic practices, where the percentage of tomato roots with galls remained below 1%. Marketable yield of tomato exceeded 35 Mg ha(-1) following all land management strategies except the strip-tillage/bahiagrass program. Marketable yield declined by 11, 14, and 19% when tomato was grown in consecutive years following a bahiagrass, weed fallow, and disk rotation. The composition of fungal internal transcribed spacer 1 (ITS I) and bacterial 16S rDNA amplicons isolated from soil fungal and bacterial communities corresponded with observed differences in the incidence of Fusarium wilt and severity of root galling from Meloidogyne spp. and provided evidence of an association between the effect of land management practices on soil microbial community structure, severity of root galling from Meloidogyne spp., and the incidence of Fusarium wilt.
  • Authors:
    • Muchaonyerwa, P.
    • Chiduza, C.
    • Dube, E.
  • Source: Soil & Tillage Research
  • Volume: 123
  • Year: 2012
  • Summary: A study was conducted to determine the effects of oat (Avena sativa) and grazing vetch (Vicia dasycapa) winter cover crops and fertilization regimes on soil organic matter (SOM) in an irrigated maize-based (Zea mays L.) conservation agriculture (CA) system following four years of continuous practice. Separate plots of oat and grazing vetch cover crops were grown in winter and then maize was planted in all plots in the following summer season. The four fertilization regimes used were: (i) fertilizer applied to the cover crops and the maize crop (F1), (ii) fertilizer applied to cover crops only (F2), (iii) fertilizer applied to the maize crop only (F3) and (iv) no fertilizer applied (F4). Control plots (weedy fallows) were included and the treatments were laid out in a randomized complete block design with three replications. Soil samples from 0-5, 5-20 and 20-50 cm depths were analyzed for total SOM, particulate organic matter (POM) fractions, hot water soluble C (HWC) and C-associated with water stable macro- and micro-aggregates (WSAC). While total SOM was more concentrated in the 0-5 cm soil depth across treatments, a lack of maize fertilization (F2 and F4 regimes) significantly (P
  • Authors:
    • Kadyampakeni, D.
    • Fandika, I. R.
    • Zingore, S.
  • Source: Irrigation Science
  • Volume: 30
  • Issue: 1
  • Year: 2012
  • Summary: The performance of a bucket drip irrigation system (BDI) powered by treadle pump was evaluated on tomato and intercropped maize/bean crops, between 2005 and 2007 in Malawi. It was a split plot experiment with three replicates. The BDI system consisted of a 1,300-l tank mounted 1.5 m above ground and connected with a 32-mm mainline and 15-mm lateral lines spaced at 1 m by 0.6 m. A treadle pump was used to uplift water to the tank. Tomato and intercropped maize/bean were irrigated every 4 days. The system reduced labour and water by >25% and it showed high uniform application depth and wetted diameter. Yields were significantly different between tomato varieties ( P
  • Authors:
    • Duc, T. T.
    • De Rouw, A.
    • Valentin, C.
    • Jouquet, P.
    • Orange, D.
    • Tureaux, T. H. des
    • Huon, S.
    • Hai, A. P. H.
  • Source: Geoderma
  • Volume: 177
  • Year: 2012
  • Summary: In Vietnam soil erosion is a major environmental problem with respect to soil fertility, water quality and downstream property damages and involves 40% of total land surface. Due to a continuous and persistent decrease of soil quality under annual crops, farmers gradually convert their fields to grazing lands and their crops to fodder cultures or tree plantations. Experimental 1-m(2) field plots with three replicates each were monitored for two years (2006-2007) to evaluate the impact of three different fodder treatments (Paspalum atratum, Panicum maximum and Stylosanthes guianensis) on runoff and soil detachment in a cultivated catchment of North Vietnam. These experiments were designed to monitor at local scale the protective effect of vegetation cover against splash and rain-impacted erosion. The lowest runoffs (ca. 3.0-4.4%), sediment yields (ca. 14-19 g m(-2) yr(-1)) and soil organic carbon losses (ca. 0.7 g C m(-2) a(-1)) were obtained for P. maximum that provided the best soil protection with respect to the two other treatments. These values were low as compared to cultivated crops (cassava and rainfed rice). Soil surface characteristics (mainly biological activity and crusting) did apparently not play a key role, most likely because each plant cover provided, with its own efficiency, protection against rainfall erosivity and rapid plant regrowth wiped out traces of flow detachment. The extent of soil detachment and sediment export, mainly controlled by cut and carry operations of fodder management, was reduced by increasing slope length from 1 to 5 m. The choice of dense fodders such as P. maximum appears to be, in terms of improved livelihood and environment sustainability, an interesting issue for uplands farmers. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Gamba, F.
    • Cruz, G.
    • Scattolini, A.
    • Prieto, V.
  • Source: Agrociencia (Montevideo)
  • Volume: 16
  • Issue: 1
  • Year: 2012
  • Summary: Citrus canker, caused by Xanthomonas citri pv citri, affects all Citrus production regions worldwide with tropical or subtropical climate. This work studies the relationship between rain, temperature, susceptibility of lemon leaves, and the appearance of symptoms of canker The evolution of citrus canker symptoms during five months of vegetative growth in a lemon Lisbon type orchard with disease background were analyzed. The data used were generated in the assessment of three growth flushes in plots with six (Treatment I) and ten (Treatment II) copper oxide sprays respectively. Daily rainfall and temperature were registered every 20 minutes. The parameters of the logistic curve of disease progress were calculated. Shoot age at disease outbreak and maximum disease value were determined. Rain was assumed to initiate an infection event from which a model of hour-degree accumulation was applied to predict the date for new symptoms appearance. Under the conditions of local infection, only the rains over 10 mm produced symptoms at the predicted date according to the model used. It was demonstrated that tissue susceptibility became a secondary factor once the environmental conditions became favourable to dissemination and symptoms expression. The method used demonstrated to be an useful tool to predict the risk of new symptoms appearance and to plan monitoring of the disease.
  • Authors:
    • Wang, N. Y.
    • Mondal, S. N.
    • Sutton, B.
    • Jeyaprakash, A.
    • Palm, M. E.
    • Peres, N. A.
    • Dewdney, M. M.
    • Schubert, T. S.
    • Rascoe, J.
    • Picton, D. D.
  • Source: Plant Disease
  • Volume: 96
  • Issue: 8
  • Year: 2012
  • Summary: In March 2010, citrus black spot symptoms were observed on sweet orange trees in a grove near Immokalee, Florida, USA. Symptoms observed on fruit included hard spot, cracked spot and early virulent spot. Hard spot lesions were up to 5 mm, depressed with a chocolate margin and a necrotic, tan centre, often with black pycnidia (140-200 m) present. Cracked spot lesions were large (15 mm), dark brown, with diffuse margins and raised cracks. In some cases, hard spots formed in the centre of lesions. Early virulent spot lesions were small (up to 7 mm long), bright red, irregular, indented and often with many pycnidia. In addition, small (2-3 mm), elliptical, reddish brown leaf lesions with depressed tan centres were observed on some trees with symptomatic fruit. Chlorotic halos appeared as they aged. Most leaves had single lesions, occasionally up to 4 per leaf. The causal organism was identified as Guignardia citricarpa based on cultural, morphological and genetic (ITS) analyses. This is thought to be the first report of black spot in North America.
  • Authors:
    • Dabar, S.
    • Soni, S. N.
  • Source: Journal of Soils and Crops
  • Volume: 22
  • Issue: 1
  • Year: 2012
  • Summary: After the green revolution and the development stage of cotton production in India the acceptance of improved cotton production technology/practices was getting the prime attention for increasing their production and productivity. Cotton research schemes and several extension education programmes were introduced to offer the education and training to farmers in respect of adopting the viable and proven improved cotton production technology/practices for their practical utilization in order to increase the income. In this context study was conducted in Dhar district. Madhya Pradesh to know the technological adoption level of cotton growers and to find out the association between socio personal and economic attributes of cotton growers with level of adoption. The study was conducted in the year of 2008-09. The study revealed that in respect of overall technology adoption, maximum cotton growers 50.22% adopted high level of technology followed by 34.11% respondents who adopted medium level and 15.67% respondents adopted low level of improved cotton production technology on their farms. The high level of adoption were reported in various extent i.e. in case of irrigation management (60.00%) followed by insect control measure (58.00%), rhizobium culture (58.00%), seed treatment (55.00%), recommended dose of fertilizer (52.00%), method of sowing (47.00%), weed management (46.00%), pest control measure (41.00%) and improved variety of seed (35.00%) respectively. The Study also revealed postive nature of phenomena the relationship between socio personal and economic characteristics of cotton growers and adoption level of improved cotton production technology. The zero order correlation coefficient of characteristic of cotton growers depicted in respect of age was 0.470**, for caste 0.283**, for level of income 0.392**, for level of employment 0.468**, for social participation 0.289** and for size of family 0.431. These characteristics were found to positively significant with adoption level of cotton production technology at 0.01 level of probability respectively. On the other hand, the characteristics like size of land holding had the correlation coefficient value of 0.200*, for material possession 0.248*, for economic motivation 0.201*, for attitude towards improved practices 0.215* and for extension participation 0.247* and these values were found positively significant with adoption level of cotton production technology at 0.05 level of probability respectively.
  • Authors:
    • Foratto, L. C.
    • Salomão, L. C.
    • Quaggio, J. A.
    • Boas, R. L. V.
    • Souza, T. R. de
  • Source: Pesquisa Agropecuária Brasileira
  • Volume: 47
  • Issue: 6
  • Year: 2012
  • Summary: The objective of this work was to evaluate nutrient dynamics in soil solution after fertigated application of nitrogen, phosphorus, and potassium to orange trees. The experiment was carried out from September 2007 to October 2009, in 'Valencia' and 'Hamlin' orange orchards grafted onto citrumelo 'Swingle' rootstock. Five doses of N, P 2O 5 and K 2O (0, 25, 50, 100 and 200% of the recommended dose) were evaluated. Soil solution was extracted from 30 and 60 cm soil depths using extractors with porous cups. Eleven evaluations were done during the experimental period, with extractions beginning 12 hours after fertigation. Increasing nutrient doses decreased pH (pH-3.5, at the highest dose), and increased electrical conductivity (CE-1.5 dS m -1, at the highest dose) and the amounts of NH 4, NO 3, P, K, Mn, and Zn in the soil solution, in both sampled depths. In the months with heavier rainfall, there was nutrient potential losses by leaching, since higher concentrations of NO 3, K, and B were observed at the 60 cm soil depth. Soil solution analysis, obtained by extractors with porous ceramic cups, can be considered an auxiliary tool for monitoring and assessing nutrient availability to plants.
  • Authors:
    • Albrigo, L. G.
    • Syvertsen, J. P.
    • Melgar, J. C.
  • Source: Acta Horticulturae
  • Issue: 928
  • Year: 2012
  • Summary: The loss of leaves, branches and flowers along with bark scuffing and root exposure that can occur during mechanical harvesting (MH) has not reduced long term yields of healthy trees. Nonetheless, such visible injuries have limited the widespread adoption of mechanical harvesting in Florida's citrus industry. There was little measurable physiological stress from MH in healthy, well-managed trees as leaf water relations, CO 2 assimilation and final yield were not affected. The abscission compound CMNP, can effectively reduce fruit detachment force and result in fewer visible injuries. Late season MH of 'Valencia' sweet orange remains a major problem when young fruitlets for next crop become large enough to be harvested prematurely. We determined if winter drought stress from January to March could delay flowering and fruitlet development so they would be too small to be susceptible mechanical harvesting. Drought stress during winter delayed flowering 2-3 weeks, reduced flowering and vegetative growth but did not reduce new fruit set relative to irrigated trees. Fruit growth after the delayed bloom caught up with the irrigated treatments so final yield and fruit quality were not affected. During mechanical harvesting, previously drought stressed trees had a higher fruit removal efficiency and less loss of the smaller young fruit than continuously irrigated trees for up to three months. Thus, winter time drought stress can be an effective practice to delay flowering and to avoid young fruit loss during late season mechanical harvesting of 'Valencia' oranges. Fruitlet oleocellosis in late season mechanical harvested trees did not increase fruitlet drop nor alter internal fruit quality.
  • Authors:
    • Shu, B.
    • Zhang, J. J.
    • Wang, P.
    • Xia, R. X.
  • Source: Plant, Soil and Environment
  • Volume: 58
  • Issue: 7
  • Year: 2012
  • Summary: Communities of arbuscular mycorrhizal fungi (AMF) were studied in sod culture (SC), straw mulching (NM), and herbicide treated and no-tillage (NH) citrus orchards, respectively. The highest total colonization rate (39.47%) and hyphal length density (1.15 m/g soil) were found in SC, the highest spore numbers (1024 spores/100 g soil) in NM, while the lowest ones (31.50%, 0.94 m/g soil and 719 spores/100 g soil) in NH and they varied significantly among three different types of orchards. Total 18 AMF species belonging to five families, Acaulosporaceae (four species), Claroideoglomeraceae (two species), Gigasporaceae (one species), Glomeraceae (nine species) and Pacisporaceae (two species) were identified, and Glomus aggregatum and Claroideoglomus etunicatum were the dominant species in all surveyed plots. The redundancy analysis showed that AMF community structure was influenced greatly by pH, soil management, soil organic matter (C ox) and available phosphorus (P Olsen). In SC orchards, species richness and Shannon-Wiener index of AMF were notably higher than in other treated orchards. So, it is reasonable to select SC as the best practice in citrus orchard in order to enhance AMF benefits.