Assessment of filtermud as a carrier for legume seed inoculants

Abstract

Peat is the most commonly used carrier for Rhizobiun. Although it is the best carrier identified to date, it has some disadvantages: its suitability varies depending on -the source and it is not readily available in many parts of the world especially the tropics. Alternative carriers of uniform composition would therefore be of considerable importance. Filtermud, a byproduct of white sugar factories, is one such material which shows a lot of promise. In this study the suitability of filtermud as a carrier for legume inoculants has been assessed. Five samples each of fresh and decomposed filtermud were collected from five sugar cane factories in Kenya namely, Ramisi, Miwani, Muhoroni, Mumias and Nzoia. Australian peat used as a standard was supplied by the Agricultural Laboratories, Sefton, New South Wales, Australia. The physico±chemical properties of filtermud and peat were investigated. Fresh filtermud contained high levels of ash and exhibited high-water holding capacity compared to decomposed filtermud. Peat and decomposed filtermud had higher pH values (6.7 to 7.9) than fresh samples (5.3 to 7.0). Extractable phosphorus, organic carbon content, C/N ratio, calcium and magnesium content were all significantly higher (P = 0.05) in fresh filtermud than in decomposed filtermud. The total N level in decomposed filtermud was higher than in fresh samples. There was however no significant difference between the levels of K and Na in the two types of filtermud. Compared to filtermud, peat exhibited a very low P content. However, the levels of total N, organic carbon, K and Na were highest ~hile the C/N ratio, Ca and Mg values were similar to those of fresh and decomposed filtermud. The plate"cou~t method was used for the enumeration of rhizobia. Irrespective of the degree of decomposition or source, filtermud-based inoculants compared well as a carrier with peat-based inoculants. This was judged from the growth and survival of R. phaseoli strain NUM 406 within a five to six months period during which cell densities of 108/g of carrier were sustained for all carriers. The effect of storage temperature on growth and . survival of R. phaseoli strain NUM 406 and R. japonic un strain NUM 504 was also determined using only decomposed filtermud from Muhoroni and peat as carriers. Storage at 40C did not significantly increase rhizobial numbers while a maximum viable count of 10 rhizobia/g of carrier was obtained when inoculants were stored at 2800 for three mDnths. No viable cells were "however recovered from inooulants stored at 400C for one -month. Based on rhizobial survival on seeds, it was observed that 40% gum arabic was a better sticker than 10% sucrose solution with both carriers when sprinkler and slurry methods of seed inoculation were adopted. Tests on effectiveness were performed using Rhizobium cultures applied as broth, peat-based and filtermud-based inoculants. Nodulation and N2- fixation were also assessed in Leonard jars under greenhouse conditions. Soybean (Glycine m ax L. Merrill) cv. "Bossier" and the common bean (Phaseolus vulgaris L.) cv. "Canadian wonder" were planted in N-free vermiculite in Leonard jars. Measurements of dry matter yield indicated that the effect of inoculation with filter mud based inoculant did not differ significantly (P = 0.01) from peat-based inoculant. From these investigations based on carrier materials from Kenya, it has been concluded that filtermud is a good carrier for inoculant production. Filtermud is easily available in large qu?-ntities at very low cost.