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Suitability of composts for an acid-loving plant: highbush blueberry
Highbush blueberry (Vaccinium corymbosum L.) is adapted to soils with high organic matter and pH of 4.5-5.5. Coniferous sawdust is the blueberry industry standard soil amendment and mulch in the Pacific Northwest, USA. However, sawdust prices are increasing, and its availability is becoming limited. Therefore, many blueberry producers
are interested in compost as an alternative to sawdust, which might also reduce the need for nitrogen (N) fertilizers. Our objectives were to: (i) estimate elemental S (So) rate needed to acidify compost to target pH for blueberry, and (ii) evaluate diverse composts vs. sawdust as soil amendments in plant growth trials under low and adequate N fertilization
regimes.
Further Authors:
J.S. Owen Jr. - Oregon State University, Corvallis
B.C. Strik - Oregon State University, Corvallis
D.R. Bryla - Oregon State University, Corvallis
R.C. Costello - Oregon State University, Corvallis
The compost feedstocks were animal manures (horse or dairy manures; solids + bedding) or plant materials [yard debris (grass + woody prunings from urban landscape maintenance), deciduous tree leaves (from street sweeping), mint (leaves and stems recovered after steam distillation of peppermint oil) or bark (aged conifer bark composted with fine sawdust and municipal wastewater treatment biosolids)]. Finished compost pH was usually 7.5-8.5, except for the bark compost, which had a pH of 5.2. Composts were titrated with dilute sulphuric acid to determine their capacity to buffer pH. Compost acidification to pH 5 required an average of 10 g So/kg across all feedstock categories. Dairy and mint composts had the highest S requirement, and the most variable compost acidification requirements (within a feedstock) were found among dairy manure (8-28 g S/kg; n = 5) and horse manure composts (4-12 g S/kg; n = 4). Yard debris compost had moderate S requirement (9 g S/kg). Bark compost did not require acidification. To evaluate compost suitability, two plant growth trials were conducted in pots in acid mineral silt loam soil (pH 5) amended with a high rate of compost or sawdust (30% by volume). Trials were performed in winter in a greenhouse (4- L pots; Jan-May) and outdoors in summer (14-L pots; May-Sept). Soil pH (after compost amendment) was predicted by the pH buffering capacities of composts. Plant growth was strongly affected by soil pH. Shoot and root growth decreased as soil pH increased from 5 (acidic) to 7 (neutral). Plants usually grew better in plant-derived composts (bark, yard debris, or deciduous tree leaf, but not mint) than in manure-derived composts (dairy or horse). Acidification of composts with finely ground So increased plant growth. At low levels of N fertilizer addition (Greenhouse Trial), plants grew better with compost than with sawdust. At a higher N fertilizer rate (Outdoor Trial), plant growth with the best performing composts was equivalent to sawdust. Composts with C:N near 20 produced good growth in both trials. Plant growth response to compost was not related to compost NO3-N analyses and was good in compost treatments with relatively low NO3-N. Most composts contained soluble salt (EC) levels considered high for blueberry. Yard, leaf, and bark composts had the lowest EC (< 1), while EC in horse, dairy, and mint composts averaged 1.8. 2.5, and 6.1, respectively (1:10 compost: water method). However, compost EC did not appear to be of primary importance in determining plant response to compost. In fact, plants grew better in composts that had been acidified with S, even though compost EC was elevated by So oxidation to sulphate. Salts were rapidly leached from pots in our trials, limiting the duration of plant exposure to high EC. We conclude that composts with pH < 6 and EC < 2 are ideal soil amendments for blueberry. Composts with higher EC may be acceptable when leaching of salts is assured, or when compost is applied as mulch. Composted woody plant materials (C:N near 20), acidified with finely ground S, are the most promising composts for blueberry. Finely ground S dust reacted quickly in compost, achieving full reaction in 2-4 weeks. The So application rate can be customized to match compost buffering capacity using our quick test method (3-d incubation with dilute sulphuric acid).
| Copyright: | © European Compost Network ECN e.V. | |
| Quelle: | Orbit 2012 (Juni 2012) | |
| Seiten: | 8 | |
| Preis inkl. MwSt.: | € 8,00 | |
| Autor: | Dr. Dan M. Sullivan  | |
| Artikel weiterleiten | In den Warenkorb legen
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