Single tree influence on organic forms and transformation of Nitrogen in arid soils

Effect of fourteen tree species on enrichment of different organic fractions of N and transformation of added fertilizer N was studied. Results were compared with the values of nearby cultivated field. Soil under the canopy of most trees had higher total N than outside canopy or cultivated field. Tree species differed in selective build up of different N fractions. Simmondsia chinensis (Sc) and Acacia pellita (Ap) showed selective enrichment of amino acid and hydrolysable NH₄-N, respectively. Prosopis cineraria (Pc), Colophospermum mopane (Cm) and Hardwickia binata (Hb) selectively enriched amino acids and amino sugar-N. Acacia aneura (Aa) and Acacia nilotica (An) enriched hydrolysable NH₄-N and amino acid-N whereas Acacia ampliceps (Aam), Eucalyptus camaldulensis (Ec) and Acacia eriopoda (Ae) enriched hydrolysable NH₄-N and amino sugar-N. Changes in these fractions did not reflect any relationship with leaf lignin: N ratio. Nitrogen added in the soil under the canopy of Tu, Aa, Ab, Ap, Aam, Ec and Prosopis juliflora (Pj) nitrified after a longer delay period than control (cultivated field soil, Cfs) whereas the opposite was true for rest of the species. Use of these results in identifying the species that are more suitable to companion crops under “parkland agro-forestry” system and N management is discussed in this paper.