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Clyde W. Fraisse, Zhengjun Hu, and Eric H. Simonne

production (as a response to a low probability of leaching rainfall occurrence) and, conversely, if a high probability in leaching rain occurrence would justify an increase in fertilization recommendation. Ultimately, as illustrated in the wheat and canola

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Jeff B. Million, Thomas H. Yeager, and Joseph P. Albano

irrigation demand. Beeson (2006) found that 20% MAD produced acceptable sweet viburnum growth. By minimizing leaching volume, ET-based irrigation has the potential to reduce nutrient leaching losses during production and, therefore, allow smaller quantities

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Rangjian Qiu, Yuanshu Jing, Chunwei Liu, Zaiqiang Yang, and Zhenchang Wang

when irrigated with saline water, with an adverse effect on fruit yield ( Ben-Gal et al., 2008 ; Munns, 2002 ). To alleviate the effects of salinity stress on plants, the application of extra water for the leaching of salts (e.g., Na + , Ca 2+ , and Mg

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J.P. Syvertsen, M.L. Smith, and B.J. Boman

Effects of salinized irrigation water on tree canopy and root growth, water use, foliar nutrition, and leaching losses below the rootzone were studied during a 2-year period using single tree lysimeters. Eighteen 6-year-old `Valencia' orange trees on either Carrizo citrange (CC) rootstock or sour orange (SO) rootstock were each transplanted into 7.8 m3 drainage lysimeters and irrigated with water having an electrical conductivity of 0.3, 1.6, or 2.5 dS m-1 from a 3:1 ratio of NaCl:CaCl2. Six additional trees (3 on each rootstock) were transplanted into soil without tanks. Trees outside the tanks were smaller, but nutritionally similar to the low salinity trees in lysimeters. Trees on CC were larger, had greater root densities, and were associated with less leaching of ions and nutrients into drainage water from the tanks than trees on SO. High salinity irrigation water reduced canopy growth and ET, but increased fibrous root dry weight. Trees on CC accumulated more Cl in leaves and in fruit juice than those on SO. Leaching loss of total N varied from 2-8% of that annually applied to trees, but up to 70% of the applied N and up to 80% of the applied K were leached from the blank tank with no tree. Salinized trees lost more N and K to drainage water, especially those on SO. Tree size, root density, and irrigation water quality can influence leaching losses beyond the rootzone.

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Rachid Mentag, Isabelle Duchesne, and Jacques-André Rioux

The objective of this study was to determine the persistence and leaching of the herbicide oxadiazon in five substrates. The substrate mixtures consisted of the following: peatmoss, compost, and sand in the following proportions: 1:1:0, 3:3:2, 1:1:2, 1:1:6, and 0:0:1 in 5-liter containers. Rates of oxadiazon used were 4 and 8 kg a.i./ha on two separate split-split plots. Each experimental design had three factors: five substrates, four harvest times (24 h; 1, 2, and 3 months) and five soil depths (0–2, 2–4, 4–6, 6–8, 8– cm). Only herbicide persistence and leaching from the various substrates were investigated in this experiment; therefore, we did not remove plant material. Substrate oxadiazon residues were determined by gas chromatography analysis, and it was shown that leaching was more evident in media with a lower percentage of organic matter. In addition, oxadiazon did not leach below 4 cm in conventional substrate (1 peatmoss: 1 compost: 1 sand, respectively). The persistence of oxadiazon was affected by soil composition and herbicide persisted more in substrates with great percentage of organic matter.

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Yingqian Lin, Alexa R. Wilson, and Pascal Nzokou

). For example, the incorporation of cover crops has proven to significantly reduce nitrate leaching in rubber tree plantations ( Schroth et al., 2001 ) and in cereal grass-based systems where they are reported to be more efficient in the uptake of

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Brian E. Jackson, Robert D. Wright, and Mark M. Alley

/estimate microbial activity. In addition to N immobilization, nutrient leaching in PTS has been proposed as a possible reason for the lower electrical conductivity and nutrient levels observed in PTS compared with peat-lite (PL) or PB during plant production

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Nabila S. Karam and Alexander X. Niemiera

The influence of intermittent and continuous irrigation on the growth, substrate nutrient accumulation and leaching from container-grown marigolds was determined. During a three week period. Tagetes erecta L. `Apollo' in a pine bark substrate received 12 irrigations. Each irrigation allotment was applied intermittently (multiple applications) or continuously (single application). Irrigation occurred when bark reached a targeted water content; irrigation water contained a complete nutrient solution. Leachates were cumulatively collected for each container and analyzed for N; plant dry weight. size, and nutrient composition were determined. Compared to continuously irrigated plants, intermittently irrigated plants had 43% greater root dry weight, 0.7% greater N concentration, and 43% more N leached from the substrate. Shoot mass. size. K, and P concentrations, substrate (pour-through extraction) and leachate N concentration were unaffected by irrigation method. Results demonstrated that. compared to conventional irrigation practices, intermittent irrigation was an effective method to reduce fertilizer effluent and increase N absorption for container-grown plants.

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Arleen Godoy and Janet C. Cole

Commercially propagated `Halward's Silver' spirea (Spiraea nipponica Maxim.) bareroot cuttings and cuttings with substrate around the roots (plugs) were transplanted into 3.8-L containers and fertilized with various P fertilizers to determine the effect of fertilizer source on P leaching and plant growth. The following fertilizer treatments were applied: 1) 100% of the recommended rate of P from controlled-release fertilizer (CRF), consisting of 22N-2.6P-10K; 2) 100% of P from triple superphosphate (TSP, 0N-20P-0K) with N and K provided by 22N-0P-10K CRF; and 3) 50% of P from CRF, consisting of 22N-1.3P-10K, plus 50% of P from TSP (CRF/TSP). The most P leached from cuttings transplanted as plugs or bareroot and fertilized with TSP, while the least P leached from cuttings transplanted as plugs and fertilized with CRF or CRF/TSP. Plants fertilized with CRF/TSP generally had larger root dry weights than did plants fertilized with CRF or TSP. Plants fertilized with CRF had the smallest stem dry weights. Shoot-to-root (S/R) ratio was largest in plants transplanted as plugs in substrate amended with TSP, but cuttings transplanted bareroot into CRF-amended substrate had the highest S/R ratio and the lowest stem P concentration. Incorporation of CRF/TSP into the container substrate can reduce P leaching compared with incorporation of TSP, and can increase root and stem dry weights of plants transplanted as plugs compared with incorporation of CRF.

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Emmanuel Genio, Tom Garrett, Greg Hoyt, Gary Wells, Larry Bauer, Dean Batal, Doug Sanders, and Contact G. Wells

The cost-effectiveness of using winter cover crops to reduce nitrogen leaching was estimated. Costs were based on cucumber and sweetpotato grown in rotation, three fertilizer application levels (0, 60, and 120 kg N/ha), and three winter covers (weeds/bare, wheat, and clover). Soil N was measured in 15-cm intervals to a depth of 90 cm at the 1993 harvest and 1994 planting. The cover crop biomass was also analyzed. Nitrogen trapping by wheat and clover was compared to bare ground with adjustment for N fixing by clover. Four scenarios—sweetpotato/both covers/high N and cucumber/wheat cover/low and medium N—yielded increased leaching compared to their bare ground counterparts. Leaching prevented from the other scenarios ranged from 1.07 to 20.11 kg·ha–1. Costs, yields, and vegetable prices were used to calculate profit changes from the bare ground method on a dollar/kg basis. Profit changes ranged from negative $2372.74/kg for cucumber/wheat cover/high fertilizer to the only positive change of $16.53 for sweetpotato/clover/medium fertilizer. Negative costs resulted from yield increases when nonwinter weed covers were used.