ABSTRACT

Three field experiments were conducted at the National Root Crops Research Institute (NRCRI), Umudike experimental field (located on longitude 07˚ 33̍ E and latitude 05˚ 29̍ N and at an elevation of 122 m above sea level in the rainforest agro-ecological zone of Nigeria) in 2014 and 2015 cropping seasons. The experiments were laid in a randomized complete block design (RCBD) with three replications. Each plot size was 6m x 4m (24m²). Land equivalent ratio (LER) and Gross monetary returns (GMR) and net returns (NR) were used to assess the productivity of the intercropping systems. The first experiment was to determine the effect of eggplant population on growth and yield of component crops in sweetpotato/eggplant intercropping system. It consisted of four eggplant populations (10,000; 20,000; 30,000 and 40,000 plants/ha) and two sweetpotato varieties of Umuspo 1 and TIS 87/0087 at 33,333 plants/ha each. The second experiment was on the effect of time of introduction of eggplant in sweetpotato/eggplant intercrop. There were three different times of introduction such as simultaneous planting of eggplant and sweetpotato; eggplant 2 weeks before planting (WBP) and 2 weeks after planting (WAP) sweetpotato varieties; eggplant 4 WBP and 4 WAP sweetpotato varieties. The third experiment evaluated the effect of organic and inorganic fertilizers application on growth and yield of component crops of sweetpotato/eggplant intercrop. The treatments were made up of 3 rates of NPK 15:15:15 fertilizer (0, 300 and 600 kg/ha) and 2 levels (5 and 10t/ha) of poultry manure (PM).  In the first experiment, intercropping reduced the growth and yield parameters of eggplant and sweetpotato. Optimum yield was achieved at mixture of 10,000 eggplant + 33,333 sweetpotato (plants/ha). Land equivalent ratio (LER) in the two years of study was mostly above 1.00. Best performance (1.79) was obtained from 10,000 eggplant + 33,333 sweetpotato (plants/ha) in 2014 and (1.60) from 20,000 eggplant + 33,333 sweetpotato (plants/ha) in 2015. The best gross monetary returns (GMR) and net returns (NR) for both years were from a population of 10,000 eggplant + 33,333 sweetpotato (plants/ha).  In the second experiment, the result showed that intercropping decreased growth and yield parameters of eggplant and sweetpotato. Simultaneous planting of eggplant and sweetpotato was the best time of introduction. LER for both years were above unity for all times of introduction but the best productivity in both years was obtained with simultaneous planting of eggplant and sweetpotato. The highest GMR and NR for both years also came from simultaneous planting of eggplant and sweetpotato. The result of the third experiment indicated also that intercropping reduced the growth and yield parameters of eggplant and sweetpotato. LER in all the applications were above unity, with the application of 300kg/ha of NPK 15:15:15 fertilizer + 5t/ha PM giving the best result. The same trend was observed with the GMR and NR. In both years of study, intercropping was more productive than sole cropping and gave greater revenue.  The greatest net return in mixture was obtained when NPK fertilizer was applied at 300kg/ha and poultry manure at 5t/ha on average. From the results obtained intercropping sweetpotato and eggplant at mixture of 33,333 sweetpotato + 10,000 eggplant plants/ha; simultaneous planting of sweetpotato and eggplant; and application of 300kg/ha of NPK 15:15:15 fertilizer + 5t/ha PM were recommended for maximum crop productivity and income generation.