• Authors:
    • Oberson,A.
    • Frossard,E.
    • Buehlmann,C.
    • Mayer,J.
    • Maeder,P.
    • Luescher,A.
  • Source: Plant and Soil
  • Volume: 371
  • Issue: 1-2
  • Year: 2013
  • Summary: Symbiotic dinitrogen (N-2) fixation is the most important external N source in organic systems. Our objective was to compare symbiotic N-2 fixation of clover grown in organically and conventionally cropped grass-clover leys, while taking into account nutrient supply gradients. We studied leys of a 30-year-old field experiment over 2 years in order to compare organic and conventional systems at two fertilization levels. Using N-15 natural abundance methods, we determined the proportion of N derived from the atmosphere (PNdfa), the amount of Ndfa (ANdfa), and the transfer of clover N to grasses for both red clover (Trifolium pratense L.) and white clover (Trifolium repens L.). In all treatments and both years, PNdfa was high (83 to 91 %), indicating that the N-2 fixation process is not constrained, even not in the strongly nutrient deficient non-fertilized control treatment. Annual ANdfa in harvested clover biomass ranged from 6 to 16 g N m(-2). At typical fertilizer input levels, lower sward yield in organic than those in conventional treatments had no effect on ANdfa because of organic treatments had greater clover proportions. In two-year-old leys, on average, 51 % of N taken up by grasses was transferred from clover. Both, organically and conventionally cropped grass-clover leys profited from symbiotic N-2 fixation, with high PNdfa, and important transfer of clover N to grasses, provided sufficient potassium- and phosphorus-availability to sustain clover biomass production.
  • Authors:
    • Lemke, R. L.
    • Vandenbygaart, A. J.
    • Campbell, C. A.
    • Lafond, G. P.
    • McConkey, B. G.
    • Grant, B.
  • Source: Canadian Journal of Soil Science
  • Volume: 92
  • Issue: 3
  • Year: 2012
  • Summary: Carbon sequestration in soil is important due to its influence on soil fertility and its impact on the greenhouse gas (GHG) phenomenon. Carbon sequestration is influenced by agronomic factors, but to what extent is still being studied. Long-term agronomic studies provide one of the best means of making such assessments. In this paper we discuss and quantify the effect of cropping frequency, fertilization, legume green manure (LGM) and hay crops in rotations, and tillage on soil organic carbon (SOC) changes in a thin Black Chernozemic fine-textured soil in southeastern Saskatchewan. This was based on a 50-yr (1958-2007) crop rotation experiment which was initiated on land that had previously been in fallow-wheat ( Triticum aestivum L.) (F-W), or F-W-W receiving minimum fertilizer for the previous 50 yr. We sampled soil in 1987, 1996 (6 yr after changing from conventional tillage to no-tillage management and increasing N rates markedly) and again in 2007. The SOC (0-15 cm depth) in unfertilized F-W and F-W-W appears not to have changed from the assumed starting level, even after 20 yr of no-till, but SOC in unfertilized continuous wheat (Cont W) increased slightly [not significant ( P>0.05)] in 30 yr, but increased more after 20 yr of no-till (but still not significant). No-till plus proper fertilization for 20 yr increased the SOC of F-W, F-W-W and Cont W in direct proportion to cropping frequency. The SOC in the LGM-W-W (unfertilized) system was higher than unfertilized F-W-W in 1987, but 20 yr of no-tillage had no effect, likely because grain yields and C inputs were depressed by inadequate available P. Soil organic carbon in the two aggrading systems [Cont W (N+P) and F-W-W-hay(H)-H-H (unfertilized)] increased significantly ( P<0.05) in the first 30 yr; however, a further 20 yr of no-tillage (and increased N in the case of the Cont W) did not increase SOC suggesting that the SOC had reached a steady-state for this soil and management system. The Campbell model effectively simulated SOC changes except for Cont W(N+P), which it overestimated because the model is ineffective in simulating SOC in very fertile systems. After 50 yr, efficiency of conversion of residue C inputs to SOC was negligible for unfertilized F-W and F-W-W, was 3 to 4% for fertilized fallow-containing systems, was about 6 or 7% for Cont W, and about 11% for the unfertilized F-W-W-H-H-H systems.
  • Authors:
    • Paoletti, M. G.
    • Marini, L.
    • Nascimbene, J.
  • Source: Environmental Management
  • Volume: 49
  • Issue: 5
  • Year: 2012
  • Summary: The majority of research on organic farming has considered arable and grassland farming systems in Central and Northern Europe, whilst only a few studies have been carried out in Mediterranean agro-systems, such as vineyards, despite their economic importance. The main aim of the study was to test whether organic farming enhances local plant species richness in both crop and non-crop areas of vineyard farms located in intensive conventional landscapes. Nine conventional and nine organic farms were selected in an intensively cultivated region (i.e. no gradient in landscape composition) in northern Italy. In each farm, vascular plants were sampled in one vineyard and in two non-crop linear habitats, grass strips and hedgerows, adjacent to vineyards and therefore potentially influenced by farming. We used linear mixed models to test the effect of farming, and species longevity (annual vs. perennial) separately for the three habitat types. In our intensive agricultural landscapes organic farming promoted local plant species richness in vineyard fields, and grassland strips while we found no effect for linear hedgerows. Differences in species richness were not associated to differences in species composition, indicating that similar plant communities were hosted in vineyard farms independently of the management type. This negative effect of conventional farming was probably due to the use of herbicides, while mechanical operations and mowing regime did not differ between organic and conventional farms. In grassland strips, and only marginally in vineyards, we found that the positive effect of organic farming was more pronounced for perennial than annual species.
  • Authors:
    • Nyakatawa, E. Z.
    • Reddy, S. S.
    • Reddy, C. K.
  • Source: International Journal of Agriculture & Biology
  • Volume: 14
  • Issue: 1
  • Year: 2012
  • Summary: Nitrogen uptake pattern by cotton (Gossypium hirsutum L.) at different growth stages in response to long-term application of poultry litter (PL) in a no-till system (NT) was studied on a silt loam soil in 2009. The study was done in plots that were established in 1996 at TVREC, Belle Mina, AL, USA. Treatments included were three tillage [conventional tillage (CT), mulch-tillage (MT), and no-tillage (NT)] two cropping systems tot ton-lye (C-R; cotton in summer & cereal rye cover crop in winter), and cotton-fallow (C-F; cotton in summer & fallow in winter)] and two sources of nitrogen [PL at 100 and 200 kg N ha(-1) and ammonium nitrate (AN) at 100 kg N ha(-1)] Out of all treatment combinations only 11 important treatments were selected and arranged in a randomized complete block design and replicated 4 times. Results in 2009, showed that NT system can supply equal quantity of nitrogen compared to CT at all growth stages. No-tillage recorded similar growth, yield and total nitrogen uptake compared to CT. Application of PL at 100 kg N ha(-1) showed significantly superior plant growth compared to AN at early growth stage, but the differences disappeared as the plant growth progressed. Similar yields and nitrogen uptake were observed with application of either PL or AN at 100 kg N ha(-1). Application of a double rate of PL (200 kg N ha(-1)) resulted in significantly higher nitrogen uptake compared to that of PL or AN at 100 kg N ha(-1), but a significant yield advantage was not observed with this higher rate. Of the total nitrogen extracted by cotton at maturity, 50% uptake was completed by early flowering stage and 97% was completed by boll development stage. At maturity, the majority of nitrogen (52%) was partitioned into seeds, while the rest was distributed into leaves (16%), stems (18%) and reproductive parts (14%). winter rye cover crop did not influence nitrogen uptake. (C) 2012 Friends Science Publishers
  • Authors:
    • Frigo, E. P.
    • Marins, A. C. de
    • Santos, R. F.
    • Souza, S. N. M. de
    • Borsoi, A.
    • Secco, D.
  • Source: Journal of Food, Agriculture, and Environment
  • Volume: 10
  • Issue: 1; Part 2
  • Year: 2012
  • Summary: Soil organic matter is of fundamental importance to improve the structure and retention of water and nutrients. This assay aims at evaluating the dynamic of organic matter in a clayey oxisol under three tillage systems, five periods and in five depths. The experiment was conducted in the Experimental Center of Agricultural Engineering in the State University of Western Parana (UNIOESTE), in Cascavel city, Parana, Brazil, in a red latosol (usually known as oxisol) from clayey to very clayey texture (600 g kg -1 clay; 320 g kg -1 silt and 80 g kg -1 sand) basalt substrate and soft-wavy relief. The area is geographically set by the coordinates 24degrees48′ south latitude and 53degrees26′ west longitude, 760 m average height. The treatments were composed of three soil tillage systems: CT conventional tillage=disc plowing followed by harrowing to level; RT reduced tillage=scarification without a following harrowing to level; and NT no-till farming=implantation of crops on the stubble of the previous crop. The depths of soil sample extractions, for the determination of organic carbon content, in each tillage system, were as follows: 0.0-0.025; 0.025-0.05; 0.05-0.10; 0.10-0.20 and 0.20-0.30 m. Organic carbon content was determined in accordance with the Walkley-Black methodology, from years 2006 to 2010. The experimental design used was a 5*3*5 factorial (five periods, three tillage systems and five depths). Tukey's test was applied to compare the average of treatments, with the significance level at 5%. After five years, NT showed an increase of 3.5% and 4.8% in organic carbon contents, related to CT and to RT, respectively.
  • Authors:
    • Seufert, V.
    • Ramankutty, N.
    • Foley, J. A.
  • Source: Nature
  • Volume: 485
  • Issue: 7397
  • Year: 2012
  • Summary: Numerous reports have emphasized the need for major changes in the global food system: agriculture must meet the twin challenge of feeding a growing population, with rising demand for meat and high-calorie diets, while simultaneously minimizing its global environmental impacts. Organic farming - a system aimed at producing food with minimal harm to ecosystems, animals or humans - is often proposed as a solution. However, critics argue that organic agriculture may have lower yields and would therefore need more land to produce the same amount of food as conventional farms, resulting in more widespread deforestation and biodiversity loss, and thus undermining the environmental benefits of organic practices. Here we use a comprehensive meta-analysis to examine the relative yield performance of organic and conventional farming systems globally. Our analysis of available data shows that, overall, organic yields are typically lower than conventional yields. But these yield differences are highly contextual, depending on system and site characteristics, and range from 5% lower organic yields (rain-fed legumes and perennials on weak-acidic to weak-alkaline soils), 13% lower yields (when best organic practices are used), to 34% lower yields (when the conventional and organic systems are most comparable). Under certain conditions - that is, with good management practices, particular crop types and growing conditions - organic systems can thus nearly match conventional yields, whereas under others it at present cannot. To establish organic agriculture as an important tool in sustainable food production, the factors limiting organic yields need to be more fully understood, alongside assessments of the many social, environmental and economic benefits of organic farming systems.
  • Authors:
    • Everts, K. L.
    • Zhou, X. G.
  • Source: Plant Disease
  • Volume: 96
  • Issue: 3
  • Year: 2012
  • Summary: Multiple applications of fungicides are used to manage anthracnose caused by Colletotrichum orbiculare and gummy stem blight caused by Didymella bryoniae, the two most common and destructive diseases on watermelon ( Citrullus lanatus) in the mid-Atlantic region of the United States. To develop a sustainable, nonchemical management option, a split-plot experiment was conducted over 3 years to evaluate the effects of a no-till hairy vetch ( Vicia villosa) cover crop on disease severity, plant growth, and fruit yield compared with two conventional bedding systems and fungicide application. The main plots were bedding strategies consisting of bare ground, polyethylene covering, or a hairy vetch cover crop that was planted in the fall, killed the following spring, and left on the soil surface as an organic mulch. The subplots were a nonfungicide control or a weekly application of a standard fungicide program. Hairy vetch mulch provided greater than a 65% reduction in the area under the disease progress curves of anthracnose and gummy stem blight and greater than an 88% decrease in diseased fruit compared with bare ground or polyethylene mulch. The reductions were comparable with those achieved by fungicide applications. Watermelon vine lengths in plots with hairy vetch were similar to or greater than those in plots with polyethylene or bare ground that were treated with fungicides. Marketable fruit in plots with hairy vetch was higher compared with bare ground in 2 of 3 years and was similar to that in plots treated with fungicides in all 3 years. Addition of fungicide application to hairy vetch treatment further reduced anthracnose in 1 year and gummy stem blight in 2 years but did not significantly increase fruit yield in all 3 years. This is the first demonstration that a no-till hairy vetch production system can reduce anthracnose and gummy stem blight on watermelon and that the production system has the potential to mitigate damage caused by these diseases.
  • Authors:
    • Pannacci, E.
    • Onofri, A.
    • Graziani, F.
    • Tei, F.
    • Guiducci, M.
  • Source: European Journal of Agronomy
  • Volume: 39
  • Year: 2012
  • Summary: Long-term effects of organic (ORG) and conventional low-input (CONV) farming systems on size and composition of weed seedbank were assessed in 2007 in central Italy, in an on-farm experiment set up in 1996. In this experiment, six rotations (R1-R6) were considered, basically consisting on the same crop sequence with different starting points, i.e. (1) legume crop (soybean/field bean/common pea), (2) vegetable crop (pepper/melon), (3) winter cereal (soft/durum wheat), (4) summer cereal (maize) (5) industrial vegetable (processing tomato), (6) winter cereal (soft/durum wheat). All rotations were established both in ORG and in CONV, in strict adherence to EU regulations (ORG: EU reg. 2092/91; CONV: EU reg. 2078/92). Intercrops with green manuring purposes were included in ORG, while weed control was performed mechanically in ORG and chemically/mechanically in CONV. Weed seedbank was determined on 10 soil samples (0-0.30 m depth) in each plot and seeds were directly extracted, identified and counted. In all rotations, the adoption of ORG resulted in a significant increase in weed seedbank density, particularly in the case of summer weed species ( Portulaca oleracea L., Amaranthus retroflexus L. and Chenopodium album L.), which are more competitive and difficult to control in summer crops under organic farming systems in the Mediterranean climates. Small differences between ORG and CONV were found in terms of number of weed species (23 in ORG and 20 in CONV, on average), but the index of diversity in CONV was on average higher than in ORG. Furthermore, the most dominant weeds in CONV represented a lower percentage of total seedbank (40%, 23% and 5%, respectively, for P. oleracea, A. retroflexus and C. album in CONV and 56%, 32% and 4% for the same three weeds in ORG). These results confirm that the wider availability of effective weed control methods in integrated low-input farming systems (CONV) is helpful to maintain a low seedbank size, with a lower dominance structure. However, the adoption of ORG systems based on long rotation cycles, very competitive crops and accurate weed control, especially at the beginning of the ORG management, may be sustainable in the long run, in terms of potential weed infestation levels.
  • Authors:
    • Quideau, S.
    • Pswarayi, A.
    • Nelson, A. G.
    • Frick, B.
    • Spaner, D.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: To investigate intercropping as a management strategy to increase crop productivity and weed suppression in organic systems, spring wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.), canola ( Brassica napus L.) and field pea ( Pisum sativum L.) monocultures were compared with two-, three-, and four-crop intercrops containing wheat at two organic and one conventional site in 2006 and 2007, central Alberta, Canada. We measured crop and weed biomass, grain yield, and crop competitiveness against weeds from a replacement design in a completely randomized block experiment. Pea and canola monocrops on organic sites yielded the least of all crop treatments. Conventional crop treatments generally yielded higher than organic treatments. Few land equivalent ratios (LERs) on organic sites were significantly >1.0. Some wheat intercrops without barley showed overyielding (LER >1.0) potential. Most of the significant LERs were from three- and four-crop intercrops. More than 50% of the intercrops on organic sites significantly suppressed weeds (based on relative weed biomass) and most of these intercrops had barley in the mixture. Barley as a sole crop and in intercrops suppressed weeds better than all other intercrops and sole crops. The wheat-canola intercrop exhibited the best weed suppression of the two-crop intercrops on organic and conventional sites. The crop densities used in this study may have contributed to the extremely low pea and canola monocrop yields as well as low LERs. Due to this, our findings should be regarded as showing trends and potential from intercrops only. We therefore recommend further studies to establish ideal densities for the intercrops used.
  • Authors:
    • Fontoura, S. M. V.
    • Bayer, C.
    • Rojas, C. A. L.
    • Weber, M. A.
    • Vieiro, F.
  • Source: REVISTA BRASILEIRA DE CIENCIA DO SOLO
  • Volume: 36
  • Issue: 1
  • Year: 2012
  • Summary: Nitrogen losses from urea by ammonia volatilization are higher from no-tillage than from conventional tillage. The objective of this study was to evaluate the magnitude of this process under cool and wet spring conditions in the South-Central region of the State of Parana and to evaluate the influence of two winter cover crops (black oat and common vetch) on ammonia volatilization in no-tillage. The tillage systems were compared in a long-term tillage experiment (28 years) and the cover crops tested separately in a long-term (>15 yr) no-tillage area. Maize was grown in both experiments. Urea was applied at rates of 0, 80 and 160 kg ha -1 N in a single application in the tillage experiment and at rates of 0, 100 and 200 kg ha -1 N, split in two applications, in the cover crop experiment. Volatilization of NH 3 was measured for 20 days after urea application in a semi-open static system. Urease activity was evaluated in both experiments. The NH 3 loss rates were highest 5 days after urea application. Cumulative ammonia losses reached 18% of the applied N in no-tillage and 3% in conventional tillage. The higher losses from no-tillage may be partially related to the greatest urease activity in the soil surface layer. Ammonia volatilization was not affected by cover crops. As an isolated practice, split surface N fertilization does not ensure a decrease of NH 3 losses, which are primarily related to rain events immediately after urea application.