ISHS Acta Horticulturae 401: International Symposium on Growing Media & Plant Nutrition in Horticulture
NITROGEN DRAW-DOWN INDEX (NDI) TESTS USED WITH VARIOUS PEAT ALTERNATIVES IN RELATION TO PLANT GROWTH OBSERVATIONS |
| Authors: | N.C. Bragg, G.M. Whiteley |
| DOI: | 10.17660/ActaHortic.1995.401.37 |
| Abstract:
The search within the UK for sustainable alternatives to peat is continuing. Previous work by the first author has considered many materials including developments in the use of composted refuse and sewage as substrate additives for container grown plants. Since this earlier work it has become apparent that there is a need for some form of objective test to make initial assessments of new materials in order to know how to manage their nutrient demands and release. A nitrogen draw down index (NDI) test has recently been developed for the rapid assessment of the rate of nitrogen immobilisation in organic components of potting media over a four day incubation period. However, from our observations of plant growth in relation to nitrogen deficiency symptoms, it was concluded that the short period of the NDI test may not necessarily relate to the fluctuating demands for nitrogen assimilation by micro-organisms taking part in the degradation of the substrates components. In this paper a series of NDI tests were conducted over a 40 day period using a range of peat alternatives in parallel with a plant growth trial. Changes for the four day NDI test values over the 40 day period varied from as little as 1.02–1.05 for peat to 0.21–0.69 for the chopped heat treated rape straw (NDI values at day 10 and day 40). The results also indicate that the changes in plant growth in relation to the availability of nitrogen are correlated with changes in sequential NDI tests taken on material incubated over the same time period as the plant growth trial. | |
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