• Authors:
    • Pereira, M.
    • Torres, J.
  • Source: REVISTA BRASILEIRA DE CIENCIA DO SOLO
  • Volume: 32
  • Issue: 4
  • Year: 2008
  • Summary: A study with eight cover crops types was developed: pearl millet ( Pennisetum americanum [ Pennisetum glaucum] syn. tiphoydes), brachiaria grass ( Brachiaria brizantha [ Urochloa brizantha]), sorghum ( Sorghum bicolor), pigeonpea ( Cajanus cajan), sunn hemp ( Crotalarea juncea) and black oat ( Avena strigosa [ Avena nuda]), fallow land and conventional culture (control) in the experimental area of CEFET-Uberaba-MG, in a cerrado area to evaluate K accumulation and release. The dry mass production, crop residue decomposition in litter bags and K release were evaluated. A mathematical model was used to describe residue decomposition and K release, which calculates the decomposition constant (k) and half-time life. Pearl millet, sorghum and the sunn hemp were the cover crops that produced most dry matter while K accumulation was highest in the grasses. K release was highest in pearl millet, oats, brachiaria grass and sunn hemp in the first 42 days after handling. Brachiaria grass had the shortest half-time life and the highest K release rate.
  • Authors:
    • Fabian, A.
    • Pereira, M.
    • Torres, J.
  • Source: PESQUISA AGROPECUARIA BRASILEIRA
  • Volume: 43
  • Issue: 3
  • Year: 2008
  • Summary: This study investigated dry biomass production, decomposition rate and macronutrients release (N, P, Ca, Mg and S) of cover crops cultural residues, in a no-till savanna soil in Minas Gerais, Brazil. The cover crops tested were: pearl millet ( Pennisetum americanum syn. typhoides), brachiaria grass ( Brachiaria brizantha [Urochloa brizantha] cv. Marandu), sorghum ( Sorghum bicolor), pigeon pea ( Cajanus cajan), sunn hemp ( Crotalaria juncea) and black oat ( Avena nuda), compared to a fallow plot (control). The experiment was carried out in an Oxisol, medium texture. A randomized block design, in a split-plot array in time, with four replications, was used. Dry biomass production was evaluated 110 days after sowing. Decomposition rate was evaluated by litter bags containing cultural residues. Millet and sunn hemp were the cover crops (grass and legume) with the highest dry biomass production and N accumulation, in the two evaluation periods. The highest decomposition rate and nutrient release occurred at 42 days after desiccation. The highest values of half life were observed in dry period.
  • Authors:
    • Paspatis, E.
    • Travlos, I.
    • Psomadeli, E.
  • Source: Journal of Agronomy
  • Volume: 7
  • Issue: 2
  • Year: 2008
  • Summary: Laboratory and greenhouse pot experiments were conducted to evaluate the potential usefulness of Oxalis pes-caprae L. as allelopathic ground-cover species for integrated weed management. The effects of the extracts of several tissues and the exudates from living roots of O. pes-caprae plants were tested for their allelopathic activity on several plants. Duckweed fresh weight was significantly inhibited from phytotoxic activity of petiole tissues (and secondly leaves and stems) of O. pes-caprae. For all the kinds of tissues duckweed fresh weight was reduced with increasing extract concentrations. Besides, root exudates of Bermuda buttercup caused 62, 58 and 42% inhibition of the dry biomass production of tomato, oat and lettuce plants, respectively, confirming the remarkable allelopathic activity of this weed.
  • Authors:
    • Castoldi, G.
    • Gobbi, F.
    • Pivetta, L.
    • Costa, L.
    • Steiner, F.
    • Costa, M.
    • Tremea, A.
  • Source: Central theme, technology for all: sharing the knowledge for development. Proceedings of the International Conference of Agricultural Engineering, XXXVII Brazilian Congress of Agricultural Engineering, International Livestock Environment Symposium - ILES V
  • Year: 2008
  • Summary: The objective of this work was to evaluate the effect of two soil tillage systems (rotation and succession crops) and three fertilizations (mineral, organic and organomineral) in the wheat yield, under no-tillage system. The assay was conducted in the Experimental Station Prof. Dr. Antonio Carlos dos Santos Pessoa, located at the Nucleo of Experimental Station belonging to West Parana State University - Marechal Candido Rondon. In the winter of the 2006 was cropping the wheat in the plots in succession crops and black oat+radish+hairy vetch in the plots in rotation crops. The wheat received the mineral, organic and organomineral fertilization, while the cover crops weren't fertilized. In the summer was cropping corn in all the plots, receiving the three kind of fertilization. In the winter of the 2007 was cropping wheat in all the plots, receiving again the three kind of fertilization. The plant high and the weight of 100 grains weren't affected by the management systems and fertilizations. The succession system (wheat/corn/wheat) showed superior yield than the rotation system (green manure/corn/wheat). The organic manure showed superior hectoliter weight than mineral fertilization.
  • Authors:
    • Stoffella, P.
    • Bayer, C.
    • Wilson, P.
    • He, Z.
    • Vieira, F.
    • Baligar, V.
  • Source: Australian Journal of Agricultural Research
  • Volume: 59
  • Issue: 1
  • Year: 2008
  • Summary: This study aimed to: (1) determine the effect of P depletion and presence of Al on root and shoot growth of representative cover crops, and on their nutrient uptake; (2) characterise the composition of root exudation under P and Al stress in nutrient solution; (3) evaluate the ability of aqueous extracts of composts in reducing Al phytotoxicity. Plants of cowpea ( Vigna unguiculata subsp. unguiculata), black oat ( Avena strigosa), and lablab ( Lablab purpureus) were cultivated in different nutrient solution compositions and concentrations for 3 weeks. It was found that Al at concentration of 20 and 200 mol/L increased citrate exudation at least 8 and 24 times, respectively, for cowpea and 18 and 36 times, respectively, for lablab, as compared with the blank. However, no release of organic acids occurred due to P deprivation, suggesting that citrate exudation was a specific response to excess Al. No response in organic acid release was observed for black oat under the stress of P deficiency or Al toxicity. Although the presence of Al in solution did not significantly affect chlorophyll content in leaves, it decreased root and shoot weight, as well as root length, surface area, volume, and number of tips. Organic extracts alleviated aluminum toxicity, improving plant growth and ameliorating plant nutrition status. Yard waste extract was more effective in enhancing plant growth than GreenEdge extract in plants under Al stress.
  • Authors:
    • Kang, J.
    • Osmond, D. L.
  • Year: 2008
  • Authors:
    • Grant, C. A.
    • Li, X.
    • Burton, D. L.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: Fertilizer nitrogen use is estimated to be a significant source of nitrous oxide (N2O) emissions in western Canada. These estimates are based primarily on modeled data, as there are relatively few studies that provide direct measures of the magnitude of N2O emissions and the influence of N source on N2O emissions. This study examined the influence of nitrogen source (urea, coated urea, urea with urease inhibitor, and anhydrous ammonia), time of application (spring, fall) and method of application (broadcast, banded) on nitrous oxide emissions on two Black Chemozemic soils located near Winnipeg and Brandon Manitoba. The results of this 3-yr study demonstrated consistently that the rate of fertilizer-induced N2O emissions under Manitoba conditions was lower than the emissions estimated using Intergovernmental Panel on Climate Change (IPCC) coefficients. The Winnipeg site tended to have higher overall NO emissions (1.7 kg N ha(-1)) and fertilizer-induced emissions (-0.8% of applied N) than did the Brandon site (0.5 kg N ha(-1)), representing similar to 0.2% of applied N. N2O emissions in the first year of the study were much higher than in subsequent years. Both the site and year effects likely reflected differences in annual precipitation. The N2O emissions associated with the use of anhydrous ammonia as a fertilizer source were no greater than emissions with urea. Fall application of nitrogen fertilizer tended to result in marginally greater N2O emissions than did spring application, but these differences were neither large nor consistent.
  • Authors:
    • Van Cleemput, O.
    • Ahmed, H. P.
    • Boeckx, P.
    • Beheydt, D.
  • Source: Biology and Fertility of Soils
  • Volume: 44
  • Issue: 6
  • Year: 2008
  • Summary: In this study, we investigated N2O emissions from two fields under minimum tillage, cropped with maize (MT maize) and summer oats (MT oats), and a conventionally tilled field cropped with maize (CT maize). Nitrous oxide losses from the MT maize and MT oats fields (5.27 and 3.64 kg N2O-N ha(-1), respectively) were significantly higher than those from the CT maize field (0.27 kg N2O-N ha(-1)) over a period of 1 year. The lower moisture content in CT maize (43% water-filled pore space [WFPS] compared to 60 -65%) probably caused the difference in total N2O emissions. Denitrification was found to be the major source of N2O loss. Emission factors calculated from the MT field data were high (0.04) compared to the CT field (0.001). All data were simulated with the denitrification decomposition model (DNDC). For the CT field, N2O and N2O+N-2 emissions were largely overestimated. For the MT fields, there was a better agreement with the total N2O and N2O+N-2 emissions, although the N2O emissions from the MT maize field were underestimated. The simulated N2O emissions were particularly influenced by fertilization, but several other measured N2O emission peaks associated with other management practices at higher WFPS were not captured by the model. Several mismatches between simulated and measured NH4+, NO3-and WFPS for all fields were observed. These mismatches together with the insensitivity of the DNDC model for increased N2O emissions at the management practices different from fertilizer application explain the limited similarity between the simulated and measured N2O emissions pattern from the MT fields.
  • Authors:
    • Ngouajio, M.
    • Wang, G.
  • Source: Hortscience
  • Volume: 43
  • Issue: 6
  • Year: 2008
  • Summary: The effects of two cover crops [cereal rye ( Secale cereale L.) and oat ( Avena sativa L.)], four tillage systems [no tillage (NT), strip tillage (ST), conventional tillage with cover crops incorporated (CTC), and conventional tillage without cover crop (CTN)], and three pre-emergence herbicide rates (full rate, half rate, and no herbicide) on pickling cucumber ( Cucumis sativus L.) growth and production, weed populations, and the incidence of pythium fruit rot were studied. Weed infestations, cucumber establishment, and cucumber leaf chlorophyll content were similar between the rye and oat treatments. However, the oat treatment had higher cucumber fruit number and weight and a lower percentage of cucumber fruit infected with Pythium spp. compared with the rye treatment. The NT and CTC systems reduced cucumber stand and leaf chlorophyll content, but had equivalent cucumber fruit number and weight compared with CTN. The NT and ST had lower weed biomass and weed density than CTN and CTC. The NT also reduced the percentage of cucumber fruit affected with pythium compared with CTN and CTC. Reducing the pre-emergence herbicide rate by half did not affect weed control or cucumber fruit yield compared with the full rate. However, weeds escaping herbicide application were larger in the half-rate treatment. The experiments indicate that with the integration of cover crops and conservation tillage, it is possible to maintain cucumber yield while reducing both herbicide inputs (by 50%) and the incidence of fruit rot caused by Pythium spp. (by 32% to 60%).
  • Authors:
    • Leser, J. F.
    • Wheeler, T. A.
    • Keeling, J. W.
    • Mullinix, B.
  • Source: JOURNAL OF NEMATOLOGY
  • Volume: 40
  • Issue: 2
  • Year: 2008
  • Summary: Terminated small grain cover crops are valuable in light textured soils to reduce wind and rain erosion and for protection of young cotton seedlings. A three-year study was conducted to determine the impact of terminated small grain winter cover crops, which are hosts for Meloidogyne incognita, on cotton yield, root galling and nematode midseason population density. The small plot test consisted of the cover treatment as the main plots (winter fallow, oats, rye and wheat) and rate of aldicarb applied in-furrow at-plant (0, 0.59 and 0.84 kg a.i./ha) as subplots in a split-plot design with eight replications, arranged in a randomized complete block design. Roots of 10 cotton plants per plot were examined at approximately 35 days after planting. Root galling was affected by aldicarb rate (9.1, 3.8 and 3.4 galls/root system for 0, 0.59 and 0.84 kg aldicarb/ha), but not by cover crop. Soil samples were collected in mid-July and assayed for nematodes. The winter fallow plots had a lower density of M. incognita second-stage juveniles (J2) (transformed to Log 10 (J2+1)/500 cm 3 soil) than any of the cover crops (0.88, 1.58, 1.67 and 1.75 Log 10(J2+1)/500 cm 3 soil for winter fallow, oats, rye and wheat, respectively). There were also fewer M. incognita eggs at midseason in the winter fallow (3,512, 7,953, 8,262 and 11,392 eggs/500 cm 3 soil for winter fallow, oats, rye and wheat, respectively). Yield (kg lint per ha) was increased by application of aldicarb (1,544, 1,710 and 1,697 for 0, 0.59 and 0.84 kg aldicarb/ha), but not by any cover crop treatments. These results were consistent over three years. The soil temperature at 15 cm depth, from when soils reached 18°C to termination of the grass cover crop, averaged 9,588, 7,274 and 1,639 centigrade hours (with a minimum threshold of 10°C), in 2005, 2006 and 2007, respectively. Under these conditions, potential reproduction of M. incognita on the cover crop did not result in a yield penalty.