Effect of organic and inorganic nitrogen sources on growth, yield and oil content of sunflower grown in highly weathered soils of Morogoro

Sunflower contributes about 40% of total national cooking oil requirement in Tanzania, ranking as one of the most important cooking oil with very high nutritional value. However, its production per unit area ranges between 800 and 1100 kg/ha, the average of which is below the potential production of 1200 to 2000 kg/ha in most African countries. The low sunflower productivity is partly attributed to low soil fertility. A field experiment was therefore conducted during the 2013/2014 long and short rains season at the Sokoine University of Agriculture soil science experimental sites to determine the effect of fertilizers; farmyard manure (FYM) and inorganic nitrogen fertilizers on sunflower growth, yield and seed oil content. The treatments consisted of: control (no nitrogen fertiliser, no farmyard manure); 2 t farmyard manure (FYM)/ha applied at planting; 5 t FYM/ha applied at planting; 10 t FYM/ha at planting; 20 kg N/ha applied as UREA at 30 days after planting; 40 kg N/ha applied as UREA at 30 days after planting; 60 kg N/ha applied as UREA at 30 days after planting; 2 t FYM/ha at planting + 20 kg N/ha applied as UREA at 30 days after planting; 5 t FYM/ha at planting + 40 kg N/ha applied as UREA at 30 days after planting and 10 t FYM/ha applied at planting + 60 kg N/ha applied as UREA at 30 days after planting. The treatments were laid out in a randomized complete block design and replicated three times. Sunflower variety record was used as a test variety. Data collected included: plant height and number of leaves at 15, 30, 45, 60 and 75 days after planting (DAP); Head diameter, biomass yield, total seed yield per hectare, weight of 1000 seeds, seed oil content and total seed oil yield per hactare. All data were subjected to analysis of variance (ANOVA) using General Statistical Package (GENSTAT) and means were separated using the least significant difference (LSD) test at P = 0.05. xi The results showed that plots supplied with farmyard manure alone or in combination with inorganic N- fertilizers had significantly taller sunflower plants than the no fertilizer control plots. Application of FYM at the rate of 10 t/ha increased plant height, biomass formation, and oil content. The application of 10 t FYM/ha and 60 kg N/ha significantly increased seed yield and weight of 1000 seeds. Application of 60 kg N/ha increased plant height at 60 days after planting during the long rains season and number of leaves at 45 DAP and 60 DAP in both seasons of the experiment. Application of inorganic nitrogen fertilizers at rates lower than 60 kg N/ha did not significantly increase sunflower crop performance relative to control. It was concluded that application of fertilizers had positive impacts on crop growth, yield, yield components and percentage oil content as of sunflower. However unlike the other parameters, oil content was only increased by 10 t FYM/ha and control had higher oil content than some other treatments in both seasons. The evidence from crop performance in terms of height, head diameter, yield and yield components suggested that a combination of FYM and inorganic nitrogen fertilizers at rates of 40 kg N /ha + 5 t FYM/ha and 60 kg N /ha +10 t FYM/ha are the most promising soil fertility management practice followed by FYM alone especially to small scale farmers who cannot afford the high costs of inorganic fertilizers. It was also concluded that application of inorganic nitrogen fertilizers at rates 20 kg N/ha and 40 kg N/ha showed no significant effect on sunflower crop yields. It was therefore recommended that farmers in Morogoro to consider application of fertilizers in sunflower crop production, especially 10 t FYM/ha alone and/or combination of 60 kg N/ha + 10 t FYM/ha as an important farm management practice to obtain seed yield of more than 1 t/ha.