The Influence of N and P on Maize Yield and Yield Components in Maize/Rice Mixture in the Northern Savanna Zone of Nigeria

Most recommended fertilizer rates available for crops in the northern savanna zone of Nigeria are for crops in monoculture. In order to be able to recommend to farmers the rates of nitrogen (N) and phosphorus (P) to be applied to maize and rice in an intercropping system to increase crop yields, a field experiment was conducted at the Samaru farm of the Institute for Agricultural Research (IAR), Nigeria (Lat. 11o 11’ N and Long. 07o 38’ E) at 680 m above sea level on a sandy loam soil in 1990 and 1992. Factorial combination of four levels of N (0, 60, 120 and 180 kg ha-1) and three levels of P (0, 13.2 and 26.4 kg ha-1) were laid out in a randomized complete block design (RCBD) with four replications. Yield components of maize such as ears/m2 increased significantly (P < 0.05) with increasing levels of N and P but no significant changes were observed in shelling percentage and 100 seed weight of maize. The number of panicles/m2 and number of tillers/plant were the yield components of rice that responded significantly (P < 0.05) with increasing levels of N and P. Threshing percent and 1000 seed weight of rice were not significantly affected by increasing levels of N and P. Grain yields of maize and rice increased significantly (P < 0.05) by raising the levels of N and P. The application of 13.2 kg P ha-1 at each level of N significantly (P < 0.05) increased maize and rice yields. However, the highest grain yields of both crops were obtained when 120 kg N ha-1 and 13.2 kg P ha-1 were applied. Introduction Intercropping, the practice of growing two or more crop species on the same piece of land in a cropping season, continues to be popular and persistent among peasant farmers in the developing world (Andrews & Kassam, 1976; Willey, 1979). Surveys conducted by Norman (1975) in the former Zaria Province of Northern Nigeria revealed that 82% of land grown to crops was under mixed cropping system. The advantages which encourage these farmers to practice this system are numerous. These include (i) a reduction in the spread of pest and diseases (IITA, 1977), (ii) insurance against total crop failure and stability of income (Abalu, 1977), (iii) efficient utilization of both factors above and under ground-resources by plants with different growth periods, heights, rooting systems and nutrient requirements. Maize is one of the most popular and widely consumed cereal in the West Africa sub-region (Langyintuo, 1997). Apart from the fact that the savanna environment has been proven suitable for production of the crop in these areas, there are other important reasons for popularizing maize in the midst of millet and sorghum. Maize yields higher than all the cereals and responds better to fertilizers. Maize yields of 8–10 tonnes ha-1 have been obtained as against 4–5 tonnes ha-1 for improved millet and long duration sorghum (Kowal & Kassam, 1978). Even yields of maize in intercrops and yields after leguminous crops gave yields comparable to sole crops fertilized with 120 kg N ha-1 which was not the same with sorghum and millet (Nguimgo, Balasubramanian & Thê, 2001). Maize is also preferred to sorghum or millet due to the fact that maize ears are protected against insects and birds damage. Though most peasant farmers in the sub-region do not consume rice regularly because of its high cost, surveys showed that most people prefer it to traditional staples like cassava and maize (IITA, 1992). However, rice is now more increasingly becoming a staple food crop in most West African countries but in others, the crop is limited to occasional preparations at funerals, weddings and for religious celebrations. Both maize and rice have become important in the Nigerian goal for food sufficiency (Olu & Adepetu, 1984), and mixed cropping continues to be dominant and important system in northern Nigeria (Fisher, 1979) but not much work is done on fertilizer use to improve the yields of such crops in the system. It has also been found that intercrop components suffer from competition for resources such as nutrients, water and light within the system (Nguimgo Balasubramanian & Thê, 2001). This means that efforts should be made to reduce the competition by supplying the system with the most limiting factors, such as nitrogen, to make the system more efficient. The recommended rates of N and P for the optimum grain yields of these crops in monocultural system in northern Nigeria have been found to be 120 kg N ha-1 and 60 kg P2O5 ha-1 for maize (Balasubramanian & Mokwunye, 1976) and 90 kg N ha-1 and 60 kg P2O5 ha-1 for rice, respectively (Nossa & Vergra, 1980). Even though work done on the production of maize and rice in a mixed cropping system showed that alternating one row of maize with five rows of rice proved promising in producing component crop yields that are comparable to sole crop yields (Elemo, 1990), little work has been done to establish the rates of fertilizers to be applied to the system to increase yields of component crops. Farmers in northern Nigeria, therefore, rely on rates of fertilizers meant for sole crops to fertilize crop mixtures. This necessitated the studies of N and P levels on maize and rice that can give optimum grain yields in an intercrop system. Specifically the study was established to determine the levels at which N and P applied to maize/rice mixture would give optimum grain yield and yield components of maize and rice in an intercropping system. Materials and methods A field experiment was conducted at the Institute for Agricultural Research (IAR) farm, Samaru (lat. 11o 11’ N and long. 07o 38’ E) at 680 m above sea level in 1990 and 1992 cropping seasons. Samaru is within the northern Guinea savanna ecological zone of Nigeria with an average mono modal rainfall of about 1200 mm. The climate is warm semi-arid with temperatures ranging from 16 oC (Decem-ber) to about 50 oC in September annually. The vegetation of the area is grassland interspersed with non-canopy forming shrubs and trees. The soil texture is sandy loam and it is classified as Orthic luvisol (FAO, 1977). Soil characterization of the site in 1990 showed a pH of 4.7 in calcium chloride (CaCl2) solution. Other chemical properties were 0.021% N, 0.6% organic carbon, 23.18 p.p.m. available P and 90 mg kg-1 K. The treatments were composed of all possible combinations of four levels of nitrogen (0, 60, 120 and 180 kg N ha1) and three levels of P (0, 13.2 and 26.4 kg P ha-1) in a randomized complete block design with four replications. The gross plot size was 40.5 m2 (8.1 m × 5 m2) and a net plot 27 m2 (5 × 5.4 m2). The site was disc-ploughed and ridged at 90 cm apart by a tractor-mounted ridger for the planting of maize. Every other ridge was then flattened, levelled and raked to a fine tilth where the rice component was planted. Maize (cv. TZBSR), a late maturing variety (120 days) resistant to streak with white grain (IITA, 1975) and rice (cv. ITA 257), an early maturing variety (90–100 days), blast resistant and low shattering (IITA, 1981) were the test crops. Maize was planted three seeds per hole on ridges at 1.8 m by 0.2 m and later thinned to 2 plants per stand, 2 weeks after planting, to maintain a plant population of 55,555 plants ha-1. Rice, on the other hand, was planted six per hole at 30 cm × 30 cm which was also later thinned to two plants per hill to meet the recommended rice plant population of 222,222 plants ha-1. The plant arrangements were, therefore, alternate with one row of maize alternating five rows of rice and the mixture was the additive model since both maize and rice were held at 100%. Fertilizer application was by band placement in split application for N, with half the amount of urea (as source of N) applied 2 weeks after planting and second dose, 7 weeks after planting. Phosphorus was applied as single super phosphate at a single dose 2 weeks after planting and covered with soil. Five hoe weeding operations were carried out at 2, 4, 6, 9 and 12 weeks after planting in order to maintain a weed-free environment. Maize was harvested later than rice in both years by hand while rice was harvested by the use of a sickle. Rice and maize were harvested on the 6th and 15th October in 1990, respectively, while in 1992, harvesting was done on the 7th and 21st of October for rice and maize, respectively. The harvested ears of maize and panicles of rice from the net plots were shelled and threshed, respectively, sun-dried and winnowed. The grains were then weighed before converting each crop into per hectare bases. Other data taken included 100-grain weight of maize, 1000-grain weight of rice, number of tillers per plant for rice, shelling and threshing percentages for maize and rice, respectively. Analysis of variance was done to test the treatment effect for significance using the F-test as described by Cox & Cochran (1967). The effects of N and P and their interactions were compared using standard errors (SE+). Results Grain yield of maize Maize grain yield increased significantly (P = 0.01) in both years as levels of N increased (Table 1). In 1990 the increase in grain yield of maize was significant up to 180 kg N ha-1, while in 1992 there was no yield advantage beyond 120 kg N ha-1 (Table 1). The effect of P levels on maize yield showed that there was no significant increase in grain yield of maize beyond 13.2 kg P ha-1 in 1992 but in 1990 the increase in grain yield due to P was significant up to highest P level of 26.4 kg P ha-1 (Table 1).