African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 6, Num. 4, 1998, pp. 407-415

C. K. SSEKABEMBE

Department of Crop Science, Makerere University, P. O. Box 7062, Kampala, Uganda

Code Number:CS98043

ABSTRACT

Napier grass (Pennisetum purpureum Schum.) is extremely valuable in eastern Africa, but high biomass production is often limited by poor establishment. An experiment was carried out at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) to determine the effect of planting method on sprouting and survival of Napier cuttings for three varieties. Erect and prostrate planting methods were compared. During the period 10 to 52 days after planting, ILCA 16791 was superior in percentage sprouting, development of fully opened leaves and 10 to 15 cm long leaves, and consequently had the lowest percentage of plants failing to sprout. The erect planting method resulted in a slightly higher percentage of sprouted Napier cuttings, but, generally, planting method did not have a significant effect on sprouting, growth and plant survival. Survival varied significantly between seasons.

Key Words: Burial, erect, Napier grass variety, planting method, sprouting, survival

Le napier (Pennisetum purpurem Schum.) est extrêmementt valable en Afrique de l'Est, mais la haute production en biomasse est souvent limitée par un faible établissement. Une expérience a été conduite à l'Institut de recherche Agricole de l'Université Makerere, à Kabanyolo (MUARIK) en vue de déterniner l'effet de la méthode de plantation sur la pousse et la survie des trois variétés de bouture de Napier. Les méthodes de plantation en position érigée et à plat ont été comparées. Durant la période de 10 à 52 jours après la plantation, l'ILCA 16791 était supérieur en pourcentage de la pousse, au développement des feuilles pleinement ouverts et de 10 à 15 cm de longueur, et par conséquent, avait le plus bas pourcentage des plants ayant échoué à la pousse. La méthode de plantation en position érigée a donné un pourcentage beaucoup plus décevant sur la pousse de bouture de Napier, mais généralement, la méthode de plantation n'a pas eu d'effet considérable sur la taille, la croissance et la survie du plant. La survie a varié suivant les saisons.

Mots Clés: l'enfouissement, position érigée, variété de Napier, méthode de plantation, pousse, survie

Napier grass (Pennisetum purpureum Schum.), also called elephant grass, originates from tropical Africa (Purseglove, 1972) and is widely adapted in tropical and subtropical areas (Wolfang-Bayer, 1990). When left unpruned in fallow, it can grow as tall as 3 to 5 m. Napier grass fallow can improve soil aggregate stability (Stephens, 1967), and this improvement in soil structure probably explains why farmers in central Uganda believe that it improves soil fertility. Napier grass is often used as mulch for banana gardens in Uganda, and thus improving productivity by conserving soil moisture and also by releasing nutrients when the mulch decomposes. Napier grass is important as a fodder (Wolfang-Bayer, 1990) and hybrid Napier grass can outyield many other grasses such as Guinea grass (Panicum maximum) and Rhodes grass (Chloris gayana) (Relwani et al., 1982).

Unfortunately, Napier grass production is often limited by problems associated with its establishment (Woodard et al., 1985). Napier can be established from seed, but it is more commonly propagated vegetatively because seed yield is low and the seed loses viability soon. Hybrids can only be propagated vegetatively (Wolfang Bayer, 1990), which allows for production of genetically uniform plant stands (Woodard et al., 1985). The most common method of Napier grass propagation used by small-scale farmers in eastern Africa is a stem cutting system. Stem cuttings are inserted into the soil vertically or at an angle of 45º. The cuttings can also be buried horizontally in furrows or shallow hills. However, there has been limited research on the most effective techniques of vegetative propagation for Napier grass (Woodard et al., 1985). In Florida, USA, Woodard et al. (1985) found that one cultivar of Napier grass (N-75) was particularly sensitive to planting depth when planted horizontally in furrows, but planting depth was less critical for another cultivar (PI 300086). In the above study, planting Napier horizontally, vertically or at an angle of 45º did not significantly influence initial emergence or winter survival of the tested Napier grass varieties. Nonetheless, the study indicated cultivar differences in response to planting techniques but did not monitor subsequent growth of Napier. Furthermore, the survival of emerged plants under tropical conditions cannot be inferred from this study. Thus a study was carried out in Uganda to determine how three Napier grass varieties respond to planting method.

The experiment was carried out at Makerere University Agricultural Research Institute, Kabanyolo (0º28¹N; 32º27¹E; 1200 m a.s.l). The station soils are Oxisols with a pH of 5.6. The area has a bimodal rainfall pattern with April to May and October to November as the wettest months. The mean daily maximum and minimum temperatures of the area are about 27 and 17oC, respectively.

Treatments consisted of three Napier grass varieties and two planting methods. The varieties included a local cultivar, and an improved cultivar (KW4) which is recommended for Uganda. The third variety, ILCA 16791, is a line introduced from the International Livestock Research Institute in Ethiopia. The planting methods were planting at an angle of about 45º, and "burial" or horizontal planting. In the former method, cuttings with 2 nodes were inserted into the soil by hand while in the latter method a hoe was used to make a shallow furrow at a depth of 10 - 15 cm into which similar cuttings were laid and buried completely.

The experiment was planted on 5 October, 1994 (referred to as the first trial), and repeated with planting on April 28, 1995 (referred to as the second trial). The first trial was associated with significantly more rainfall compared to the second trial, having received 859 mm compared to 172 mm received during the duration of the second trial. The treatments were arranged in a split-plot experimental design with Napier variety in main-plots and planting method in subplots. There were 3 replications in each trial. A main plot consisted of 2 rows and a subplot consisted of one row with 15 plants (50 cm apart).

Plots were weeded regularly to maintain virtually weed-free conditions. Observations included percentage sprouting, development of 2 or more fully opened leaves (FOL), and 2 or more leaves 10 to 15 cm long, percentage of cuttings failing to sprout, and death of plants that had sprouted (survival of sprouted plants). The number of shoots developed and dry matter produced were only determined in the second trial. Observations of sprouting started 10 days after planting (DAP) and continued at 3 day intervals. A cutting was judged to have sprouted when the nodes produced a leaf. For horizontal planting, these leaves had emerged from the soil. Scoring the percentage of plants with 2 or more FOL started 16 DAP while scoring for those with leaves 10 to 15 cm long started 21 DAP. Fully opened leaves were those no longer wrapped at the node of origin. Survival of sprouted plants was recorded as the percentage of plants alive 3 months (90 DAP) after planting divided by those that had sprouted by 52 DAP. During the counting of shoots, primary and secondary shoots were differentiated. A primary shoot is the first shoot that directly arises from a node on the stem cuttings (Woodard et al., 1985); but in the study, primary shoots were those which originated at ground level and equivalent to primary tillers in cereals while secondary shoots originated from the primary shoots. Total dry matter harvested 3 months after planting was partitioned into leaf and stem dry matter using a sample of five plants from each subplot. Dry matter was determined after cutting the samples into small pieces and drying in an oven at 60ºC for 48 hours. The percentage data were subjected to arcsine transformation before statistical analysis.

Overall sprouting of Napier by the end of the sampling period (52 DAP) was greater than 70% in both trials with the exception of the local variety in the first trial. Early sprouting (10 DAP), was least for the local variety in the first trial but least with KW4 in the second trial (Fig. 1). In the second trial, KW4 improved in percentage sprouting over time, reducing the difference between it and the local variety by 22 DAP. However, in the first trial, the local variety maintained the lowest percentage sprouting throughout the sampling period. In both trials, ILCA 16791 was significantly (P<0.01) better in percentage sprouting than the other 2 varieties, from 10 DAP to 49 DAP. KW4 was significantly better than the local variety only in the first trial. ILCA 16791 also attained its maximum sprouting percentage earlier than the other varieties, and this was particularly noticeable in the first trial. On average, and particularly for the local variety, percentage sprouting was significantly (P<0.05) better during the second trial. This was particularly pronounced between 16 and 25 DAP. Hence, there are major differences among the varieties in terms of the rate of sprouting and this was greatly influenced by season in the case of the local variety. The erect method exhibited a greater percentage of sprouting only at 10 DAP (P<0.05) (Fig. 1).

In the second trial, ILCA 16791 developed the maximum number of plants with 2 or more FOL earlier than the other varieties, and more FOL (P<0.01) at 52 DAP (Fig. 2) and had more leaves of 10 to 15 cm length (Fig. 3). FOL and the development of at least 2 leaves 10 to 15 cm long was not influenced by planting method (Figs. 2 and 3).

Although the difference was not significant, the burial method exhibited a higher percentage of failed cuttings and this was particularly pronounced for the local variety during the first trial (Table 1).

TABLE 1. Effect of planting method on Napier failure to sprout