Effect of compost enriched with N and L-tryptophan on soil and maizeRizwan Ahmad1, Azeem Khalid1, Muhammad Arshad1, Zahir A. Zahir1 and Tariq Mahmood2
1 Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad-38040, Pakistan
2 Department of Agronomy, University of Arid Agriculture, Rawalpindi, Pakistan
Accepted 3 December 2007; published online 15 March 2008
Abstract - Composting provides an excellent way to manage the huge volume of organic waste and convert it into a useful soil amendment. The effectiveness of composted organic waste can be further improved by enriching and blending it with nutrients and biologically active substances. The resulting value-added composts can be used at substantially low rates such as a few hundred kg per ha compared with conventional use of organic wastes in tons per ha. This approach could have practical significance in reducing the use of chemical fertilizer for sustainable agriculture and the environment. L-tryptophan is a precursor of the growth hormone indole acetic acid and is known to stimulate plant growth at extremely low concentrations. Here, we studied the effect of composted fruit and vegetable wastes, enriched with N at 133 g kg-1 compost, with or without L-tryptophan at 10 mg kg-1 compost, on soil and maize crops. The enriched compost was applied at 300 kg ha-1 to a sandy clay loam soil either by mixing with the top 15-cm soil layer in pots or as a band placement along the maize plants grown in the field. The compost was applied alone and in combination with 40 or 80 kg ha-1 urea N and compared with a treatment containing 160 kg N ha-1, a full dose of N fertilizer alone, while P and K fertilizers were applied in all the treatments. Our results show that application of the enriched compost to soil increased aggregate stability by up to 24.8% and water retention by up to 43.1% compared with untreated control. A gradual increase in the concentration of indole acetic acid in compost, ranging from 1.02 to 3.34 mg kg-1, was observed when compost was treated with its precursor L-tryptophan. The results of pot and field experiments revealed that compost enriched with N and L-tryptophan in the presence of 80 kg N fertilizer significantly increased cob and grain yields, by up to 19.8 and 21.4%, respectively, compared with a full dose of N fertilizer. These findings suggest that enrichment of composted organic wastes with N and L-tryptophan can change them into a value-added organic product that could be used as a soil amendment at rates as low as 300 kg ha-1 to increase crop production on a sustainable basis.
Key words: auxins / biologically active substances / maize / nitrogen / organic fertilizer / organic waste / recycling soil aggregate
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