Performance of rape (Brassica napus) Grown under organic farming compared to conventional practices

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Muleya, Mukonde Patrick
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This study was carried out during the 2008/09 season under irrigated conditions. It was conducted at the University of Zambia (UNZA), School of Agricultural Sciences Field Station. The objective of the study was to determine the yield response of selected varieties of a leafy vegetable, Rape (Brassica napus) grown under organic and conventional practices and ultimately provide evidence of the potential of organic farming. The specific objective of the study was to evaluate the suitability of organic manure as a source of nutrient nitrogen for plant growth in organic production system compared to conventional system Three varieties (English giant, Nanga and Prior), three nitrogen levels (10, 20 and 50 Kg N/ha) from D-compound and three organic sources (undecomposed, partially decomposed and fully decomposed composts) under the two farming systems (conventional and organic) were used as main and sub plots respectively. A Strip-Split Plot Design was used. The yield parameters measured were number of leaves per plant, leaf width, leaf area index (LAI) and leaf yield. The nitrogen content of leaves and in the soil after harvesting were also determined. The results indicated that applied nitrogen level had a significant effect (P<0.05) on all the yield parameters measured with the highest results obtained under the rate of 50 Kg N/ha. Varieties were different for number of leaves per plant. The variety Nanga had the highest (20) number of leaves per plant while the variety English Giant had the lowest (13) number of leaves. The plants grown under conventional farming gave a significantly (P< 0.05) higher number of leaves (19) per plant compared to (16) for those under organic farming. Nitrogen levels were also significantly (P<0.05) different for leaf width. The smallest leaves were under the level of 20 Kg N/ha (7 cm) while the other two nitrogen levels the leaf widths were not significantly different. The farming methods were different for leaf width with the conventional producing wider leaves (8.85 cm) than those from organic farming (7.59 cm). The nitrogen levels were also significantly different (P< 0.05) for leaf area index (LAI). The highest LAI of 55.5 was observed under the 50 Kg N/ha while the other two were not significantly different. The varieties were not significantly different for LAI. However, significant differences for LAI were observed between conventional and organic farming. Conventional farming gave a higher LAI of 50 compared to 28.6 for organic farming. Relative higher leaf yields were obtained under 50 Kg N/ha treatment and under the variety English Giant, but there were no significant differences observed among the nitrogen levels and varieties for leaf yield. Similarly, no significant differences were observed between conventional and organic farming for leaf yield. Farming methods were significantly different for soil N with organic (0.30%) producing higher than conventional farming (0.24%). No significant differences were observed among nitrogen levels, variety and farming methods for plant tissue N. The average leaf yield of 1.6 tons/ha for the conventional and 1.2 tons/ha for the organic farming respectively were not significantly different (P< 0.05) thereby making organic farming a viable alternative to conventional practices.
Organic farming--Brassica napus-Zambia , Brassica napus