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  • 1
    Electronic Resource
    Electronic Resource
    Old tree root channels in acid soils in the humid tropics: Important for crop root penetration, water infiltration and nitrogen management (1991)
    Springer
    Plant and soil 134 (1991), S. 37-44 
    Details
    ISSN: 1573-5036
    Keywords: cassava ; Guelph permeameter ; leaching ; maize ; methylene blue ; rice ; rooting depth ; soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Under high rainfall conditions on acid soils with shallow crop root systems the rate of N leaching is high. A simple model predicts nitrogen uptake efficiency as a function of the amount of rainfall in excess of evapotranspiration, rooting depth and degree to which N leaching is retarded in comparison with water transport. Field observations on acid soils in S.E. Nigeria and S. Sumatera (Indonesia) showed that this model should be amended to include the role of old tree root channels. Crop roots can follow these channels, which are coated with partly decayed organic matter, into the acid subsoil. Measurements of water infiltration with a Guelph permeameter and a methylene blue dye showed that such channels form the major infiltration sites during rainstorms. Implications for nitrogen use efficiency and cropping pattern are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010715
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  • 2
    Electronic Resource
    Electronic Resource
    Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths (1998)
    Springer
    Agroforestry systems 43 (1998), S. 81-93 
    Details
    ISSN: 1572-9680
    Keywords: competition ; leaching ; N uptake ; subsoil ; N2 fixation ; Indonesia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched 15N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual 15N in the soil remained close to the injection points due to the joint application with a carbon source which promoted 15N immobilization. Temporal 15N uptake patterns (two-weekly leaf sub-sampling) as well as total 15N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little 15N from any depth but obtained an estimated 44–58% of its N from atmospheric N2-fixation. Gliricidia took up an estimated 21 kg N ha–1 and Peltophorum an estimated 42 kg N ha–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of 15N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022123020738
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