Influence of fertilizer combination, planting density and varieties on cassava (manihot esculenta crantz) stem yield

Cassava (Manihot esculenta Crantz), is the second staple after maize which contributes to food, feed and cash crop in Tanzania. The crop is a drought tolerant and can yield better than other crops in areas with erratic rains and in years with low total and poor rainfall distribution. However, its root yield is low due to the use of stem cuttings from land races, improper planting densities and declining soil fertility. The study was conducted to determine the effects of fertilizer combinations, planting density and variety on growth and stem yields of cassava. To evaluate the effect of fertilizing cassava plants on sprouting, growth and vigor of a subsequent crop. To assess the economic feasibility of different fertilizer combinations, improved varieties and planting density on cassava stem cuttings. One field trial and one pot experiment was conducted at TARI Ilonga, Kilosa District Tanzania. The field experiment was arranged in a split split plot in a randomized complete block design (RCBD) with variety, planting density and levels of fertilizer combinations as main, sub and sub sub factors, respectively. Cassava varieties used were Kiroba, Chereko and Mkuranga 1, planting densities of 10 000, 13 000 and 20 000 plants ha-1 and 10 fertilizer rates. Data collected were soil physico-chemical characteristics of the site, total plant height, stem height, stem diameter, number of cuttings ha-1 and number of nodes stem cutting-1. The plant data were subjected to analysis of variance (ANOVA) and means were compared using Tukey‟s honestly significance (p<0.05). Interactions of significant factors was also performed using Tukey‟s honestly significance (p<0.05). Application of N at 150N-0P-0K kg N ha-1 produced significantly higher total plant height and stem height, while planting density of 20 000 plants ha-1 and Kiroba variety produced significantly higher numbers of stem cuttings ha-1. ii There was significant interactions among all three varieties of cassava and plant density at 20 000 plants ha-1. A screen housed potted experiment was conducted for 4 weeks (28 days) using sets of stem cuttings from three cassava varieties (Mkuranga 1, Kiroba and Chereko) obtained from fertilizing mother experiment to evaluate sprouting ability (sprout growth and vigor) of a successive crop. Planting materials for a successive crop were stem cuttings harvested from stem mother crop raised from interaction of variety x planting density (13 000- and 20 000-plants ha-1) x with, and without N fertilizer use. Rooting media was river sand soil collected and homogenized through thorough mixing and sample sent for physical- chemical analysis to IITA Dar es Salaam hub soil laboratory. The stem cuttings were planted in a 4 liters plastic pot perforated at the base and filled with a 3 kg thoroughly mixed river sand soil in each of the 4 liters capacity pots. The pots were arranged in a completely randomized design (CRD). Three stem cuttings dimension 25 cm long from middle portion of stems raised from with and without fertilizing stem mother plots of the three varieties (Chereko, Kiroba and Mkuranga 1) plots were planted per pot. The soil moisture level was managed throughout the experimental period by supplying planted stems using 100 mils of rain water reserved purposely to supply moisture twice a day for each pot and the moisture for each pot was uniformly supplied early in the morning as well as late in the evening for the whole period of 4 weeks. The parameters assessed were sprouting, sprout height, and sprout fresh and dry biomass. The data collected were analyzed by analysis of Variance and significant treatments separated using Tukey‟s honestly significance test at p>0.05. The means which were statistically similar and a relative change to treatment means performance were computed. It was found that previous fertilizer applications and varying planting densities positively influenced sprouting of cassava stems of improved varieties. The sprouting ability (percentage sprouting, sprout heights, sprout fresh and dry iii biomass) of the improved cassava varieties were increased by fertilizing stem mother plots and adjustment on planting densities. For assessment of the economic feasibility of producing stem cuttings of improved varieties treated with different rates and sources of fertilizers and planted at varied densities and the economic variables used were comprised of land hire and production costs. The data on revenue were from sales of cassava stem cuttings and that of production cost which were subjected to profitability analysis through Gross Margin (GM). The results revealed the highest Gross Margin (GM) for each variety where by Chereko (89.78%) appeared the first, followed by 78.6% for Mkuranga 1 and Kiroba variety was the lowest at planting density of 20 000 plants ha-1 but the rates of fertilizer and sources were different for each variety. Chereko variety gave highest GM of TZs 13 845 535.70, (U.S. dollar 5,980.70) when it was applied with 150 kg N ha-1 from Sulphate of Ammonia and followed by Kiroba variety [TZs 8 807 405.00 (U.S. dollar 3 804.43)] applied with Urea at 75 kg N ha-1. The results revealed that appropriate use of cassava stem cuttings of improved variety, right type and rate of fertilizer use particularly nitrogen (N) and plant density of 20 000 plants ha-1 found to be necessary technologies and are recommended for massive multiplication of quality stem cuttings. The study further concluded that Chereko variety planted at a density of 20 000 plants ha-1 and applied with two splits of 150 kg N ha-1 yielded higher number of stem cuttings, reaped more profit margin and is thus recommended for massive multiplication of cassava stems in the study area. The study results from sprouting ability test of stems produced through fertilizing and non-fertilizing mother plots gathered statistical evidence that N-fertilizing stem mother plots could be considered to be an appropriate method for quality stem cuttings production in Kilosa District. . iv Thus, fertilizing stem mother plots using two splits of 150 kg N ha-1x20 000 plants ha-1 and improved varieties of cassava can be recommended for massive multiplication, improving farmers‟ income and improving sprouting ability in successive crop. Further studies on cassava stems sprouting ability and profitability analysis on stem production through fertilizing stem mother plots are of great importance.