Maize/Joint Velch Intercropping and N Fertilization Effects on Striga Infestation and Maize Grain Yield in the Southern Guinea Savanna of Nigeria

The parasitic weed Striga poses a serious threat to cereal production in sub-Saharan Africa. For many years, technological packages for the control of this weed were proposed and implemented on farmers’ fields. A study was conducted in 2012 and 2013 to determine maize/ Jointvetch (Aeschynomenehistrix) and N fertilization effect on Striga infestation and maize yield. The intercropping trial consists of six treatments, four inorganic N fertilizer levels of 0, 60, 90, 120 kg ha , alternate hill and same hill intercropping of A. histrix. The experiment was laid out in a randomized complete block design with three replicates. Alternate hill and same hill intercropping significantly (P < 0.05) reduced Striga infestationwith respect to Striga shoots per m and plot, Strigareation score and enhanced maize grain yield. There was a significant decline in the level of damage by Striga on maize in plots that received 60 – 120 kg N ha. Alternate hill and same hill intercropping had maize grain yield of 3295 kg ha -1 and 2616 kg ha which were significantly higher than those obtained without inorganic N application (306 kg ha ). Inorganic N application had a significant (P < 0.05) effect on grain yield. Lowest grain yield of 306 kg ha -1 was obtained without inorganic N application, which was significantly (P<0.05) different from those fertilized with inorganic N, that had comparable grain yields. Inorganic N fertilizer rate of 60 kg ha -1 seems to be optimum for maize. Keywords— Grain, intercropping, Jointvelch, Maize, Striga.

7 mm long producing 1.5-2 mm long seeds which are black in colour. This herbaceous plant thrives well in habitat with sandy acid and low fertility soils, sometimes in sandy loam and clay soils, and it is moderately drought tolerant. It is a fast growing and decomposing green manure with high potential as legume fallow in the humid tropics [4]. A.histrix has the ability to fix large quantities of N, thus enriching the poor tropical sav anna soils [5]. It grows wildly and widely in the southern Guinea Savanna of Nigeria.
Intercropping is a common practice in Africa. The use of intercropping host crops with legume crops is to serve as trap, wher eby the Striga soil seed bank is depleted in the long run. The trap crop stimulates Striga seeds to germinate without being parasitized, a phenomenon known as suicidal germination and improve soil fertility [6]; [7]. However, it was discovered that the species and varieties of the crops exhibit a wide variation in their ability to stimulate Striga seed germination. [8] noted that maize intercropped with groundnut (RMP12) did better than plots intercropped with cowpea (IAR, 48). In a similar study, [9]observed increased maize grain yield when groundnut was intercropped with it than with soybean. Furthermore, [10] and [11] found intercropping sorghum and millet with groundnut, to reduced S. hermonthicainfestation compared with sole cropping. Also, [10] noted that the resistant sorghum varieties supported fewer numbers of Striga shoots than the susceptible varieties. In addition, [12] observed fewer Strigashoots and higher grain yield in Strigaresistant maize. In a similar study, [13] observed that sorghum interplanted with Jointvetch (A.histrix) delayed Striga shoot emergence by about two weeks and reduced its density by about 60 % thereby, increasing sorghum grain yield by about 74 % above the control. When resistant maize variety, ACR 97 -TZL COMP. l -W was intercropped with soybean and groundnut, it consistently resulted in lower Striga incidence, infestation and severity than the farmer's local cultivar 9 (Kuchindaet al., 2003). Intercropping maize with two varieties of soybeans did not significantly reduced Striga incidence, infestation, crop syndrome reaction score and grain yield, an indication that the two soybean varieties had similar potentials for use as trap crop [14]. In the same vein, [15] have reported that intercropping Celosia argentea(Strigachaser) into sorghum reduced Striga emergence by an average of 55 % in a season and increased the yield of a susceptible sorghum variety in the field by 35 % compared to sole sorghum treatment. The objective of this experiment is to determine the effect of Jointvelch (A. histrix) intercropping with maize and N fertilization on Striga infestation and maize performancein Mokwa, southern Guinea savanna.

Experimental Site
Field experiments were conducted on a Striga infestedfield in 2012 and 2013 rainy seasons at the Teaching and Research Farm of Niger State College of Agriculture, Mokwa (09 0 18 N; 05 0 50 E), situated in the Southern Guinea savanna agro ecological zone of Nigeria. The soil of the experimental site was Alfisols with surface soil texture of sandy -loam, acidic, low in nitrogen but moderate in phosphorous. Rainfall pattern is monomodal with the rainy season starting in March or April and ending in October . Monthly rainfall during the period of study is shown in Table 1. The field was heavily infested with Strigahermonthica which makes it to be sparingly cultivated with maize over the years with no fertilizer application.

Treatments and experimental design
The treatments were four inorganic N fertilizer levels (0, 60, 90, 120 kg ha -1 ), alternate hill and same hill interplanting of A. histrix. The treatments were laid out in a randomized complete block design with three replicates. There were 18 experimental plots, such that gross plot size was 8 m × 4 m (32 m 2 ) and the net plot size was 18 m 2 , separated by 1m alley. The number of ridges in the plot was five while the length of ridge was 8 m.

Agronomic practices
The field was manually cleared and ridged using hoe at 75 cm apart in 2012 and 2013. The maize variety, SUWAN 1, obtained from premier seeds, highly susceptible to Striga was manually planted at 3 seeds per hill, spaced 50 cm within rows. The seedlings were thinned to two plants per hill at two weeks after sowing (WAS) to give a plant population of 53, 3333 plants h a -1 . Basal application of 30 kg P ha -1 as single superphosphate and 30 kg K ha -1 as muriate of potash were carried out at 2 WAS after thinning. Inorganic N fertilizer as urea was splitapplied to plots that were to receive N fertilizer. At 2 WAS, one-third of the N was applied, while the remaining two-third was applied at 6 WAS. Fertilizers were applied by side banding at about 5 cm away from the seedlings and at about 5 cm deep along the ridge. The first hoe -weeding was carried out at 3 WAS while the second weeding was at 5 WAS followed by careful hand-pulling of weeds other than Striga.

Striga infestation parameters
The number of Striga shoots per maize plant was taken by counting each Strigashoot present per maize plant stand starting from 6 WAS. The number of Striga shoots flowering was taken by counting closely the number that flowered in each plot. The number of Striga shoots per meter squared was taken by counting closely the number of Striga present in each plot per m 2 . Days to 50 % Strigashoot flowering was carried out by counting the number of days from the day the first Striga shoot emerged to the day that 50 % of Striga shoots flowered. The Striga reaction score was taken on the scale of 0 -9 using visual observation to measure mild, severe and very severe or death infestation of Striga on maize plant.

Observations on growth and yield parameters
Ten maize plants from each of the net plot were randomly tagged for periodic observation at 3, 6 and 9 WAS. The following observations made were: The maize plant population was carried out by counting individual plants at 3, 6 and 9 WAS. This is also known as plant population count and expressed in hectare. The maize plant height was observed by tagging ten plants from the inner rows at random which were used throughout for taking the measurements. The plant height was measured using meter rule from the top of the uppermost leaf to the base of the plant at 3 and 6 WAS but from the base to the tip of the tassel at 9 WAS and express ed in centimeters. Days to 50 % maize tasselling was taken through observation by counting the number of days from the sowing date to the day when about 50% of all the maize plants in each plot has tasseled and expressed in percentage. The average cob leng th of 10 harvested tagged maize plant from the inner row of each plot were taken and measured using meter rule and expressed in centimeters. The number of maize cobs from the inner rows of each plot was counted and estimated per hectare. This was done when the plant attains physiological maturity. The number of maize grain per cob was also obtained by weighing those harvested from the inner rows and shelled at harvest time. This was done by counting. 100 maize grain weights was taken from the ten harvested cobs from each plot, shelled and weighed using a weighing balance, expressed in grams.

Grain yield and yield components analysis
The maize grain yield analysis was carried out by harvesting maize ears in the two central rows leaving out the border plants at both ends (net plot of 18 m 2 ). These were shelled, air-dried and weighed. The grain yield was adjusted to 12 % moisture con tent for each plot and weighed.

III.
STATISTICAL ANALYSIS The data collected were subjected to analysis of variance (ANOVA) and means were separated using Duncan Multiple Range Test at 5 % level of probability. The statistical package used was Statistical Analysis System (SAS), version 9.2(2002).

IV. RESULTS Initial soil properties of the study area
The initial soil properties of the experimental site before the commencement of the study are shown in Table 2. The soil of the experimental site for this trial was loamy sand, acidic, low in organic carbon but moderate in nitrogen and phosphorous. The soil had a loamy sand texture which is suitable for the cultivation of maize with minimum tillage.

Vegetative growth parameters
The effects of intercropping and nitrogen fertilization on maize plant height is shown in Table 3. Maize plant height was significantly (P < 0.05) affected by intercropping and N-fertilization at 3 WAS and at 6 and 9 WAS in 2012. Plots given 60 kg N ha -1 obtained taller plants at 6 and 9 WAS which was 48 and 33 % higher than the control. The trend was slightly different in 2013 cropping season where the heights was significantly increased by intercropping and N fertilization across the sampling weeks such that plots given 120 kg N ha -1 had taller plants at 3 WAS. The application of 90 kg N ha -1 and same hill intercropping produced similar taller plants than all others except plots given 120 kg N ha -1 at 6 WAS. The trend over the two years show a consistent increase in plant height with the use of 60 kg N ha -1 in 2012 and same hill in 2013. The effect of intercropping and N fertilization on days to 50 % tasselling is shown in Table 4. Days to 50 % tasselling was significantly (P < 0.05) influenced by intercropping and N fertilization in 2012 and 2013 cropping seasons (Table 4). In this, alternate hill intercropping, 60, 90 and 120 kg N ha -1 had shorter number of days to 50 % tasselling, compared with the control which had longer days in both years though similar to same hill in 2012 only. The effects of intercropping and N fertilization on number of maize cobs are also shown in Table 4. The number of maize cobs per plot differ significantly (P < 0.05) due to intercropping and N fertilization in 2012 and 2013 rainy seasons. Application of 60 kg N in 2012 and 90 kg N in 2013 produced greater number of cobs, which were similar to plots given 90 kg N, 120 kg N and alternate hill in 2012 only. Application of 0 kg N ha -1 obtained lower number of cobs per plot in both years. Intercropping and N fertilization had a significant (P < 0.05) effect on cob length such that the use of 120 kg N ha -1 produced longer cobs than the other treatments except plots given 60 kg N ha -1 in 2013. In the same vein, application of 60 kg N ha -1 and alternate hill obtained similar longer cobs than 0 kg N ha -1 plot only in 2013.

Striga infestation
The effects of intercropping and N fertilization on Striga shoots per m -2 , Strigareation score and Striga shoots per maize plant at 9 and 12 WAS in 2012 and 2013 are shown in Tables 5, 6 and 7, respectively. Intercropping and N fertilization had a significant (P < 0.05) effect on Striga population (m -2 ) ( Table 5). In both 2012 and 2013 cropping season, Striga population was significantly reduced by 120 kg N ha -1 than 0 and 60 kg N ha -1 only at 9 WAS in 2012, while 90 kg N ha -1 and same hill were statistically similar at 12 WAS in 2012 except 0 kg N ha -1 . Similarly in 2013, application of 60 kg N ha -1 , had lower number of Striga shoots compared to the control only which had the highest at 9 WAS. At 12 WAS, 90 kg N ha -1 and same hill obtained higher number of Striga shoots, compared to 60 and 120 kg N ha -1 which had the lowest, which were also in turn not significantly different from 0 kg N and alternate hill. Strigareaction score was significantly (P < 0.05) affected by intercropping and N fertilization in both cropping seasons (Table 6). There was a significant decline in the level of damage caused by Striga on maize in plots that received 60 -120 kg N ha -1 , same hill and alternate hill in both sampling times in 2012, while the reverse was the case with 0 kg N ha -1 during this time. The trend in 2013 rainy season showed that 60 kg N had lower level of infestation at both sampling times, and were similar to 90, 120 kg N ha -1 and same hill at 9 WAS, and 120 kg N ha -1 at 12 WAS only. The application of 0 kg N ha -1 consistently had higherStriga reaction scores on maize in this study. Intercropping and N fertilization had a significant (P < 0.05) effect on Striga shoots growing with maize ( Table 7). The number of Striga shoots growing with maize was significantly reduced in alternate and same hill intercropping which were in turn similar to other treatments except 0 kg N ha -1 which obtained higher shoots at each sampling time in 2012. The trend in 2013 showed that 60 kg N ha -1 plots at 9 WAS had lower number of Striga shoots more than the 0 kg N ha -1 and same hill plots only. At 12 WAS, there was no significant difference of this treatments on this parameter.

Maize yield and yield components
The effects of intercropping and N fertilization on maize yields and yield attributes in 2012 and 2013 rain y seasons are shown in Table 8. Intercropping and N fertilization significantly (P < 0.05) affected 100 grain weight (Table 8). In 2012, application of 60 kg N was found to have heavier seeds, which were comparable to other treatments except the control in bot h years. Furthermore, grain yield was significantly (P < 0.05) affected by intercropping and N fertilization such that application of 60 kg N produced higher grain yield more than the 0 kg N ha -1 by 59.7 % and 36.6 % in 2012 and 2013, respectively. Stover yield was significantly affected by intercropping and N fertilization such that application of 120 kg N in 2012 an d alternate hill in 2013 obtained heavierstover than same hill and 0 kg N ha -1 in 2012 and 0 kg N ha -1 in 2013 only.

V. DISCUSSION
The slightly acidic nature of the soil make most soil nutrients to be available for plant uptake [16]. The low organic carbon content of the soil will necessitate incorporation of crop residues and other organic materials into the soil to increase its fertility especially N, which was low. Soil organic matter is the main source of N in the soil [16]. Available phosphorus content was moderate implying that the soil might not need application of phosphorus fertilizer in the short run for optimum yield of mai ze. The very low base saturation suggests the domination of the exchange sites by exchangeable bases with consequent low exchangeable acidity. Plant height, days to 50 % tasselling, number of cobs plot -1 and cob length were increased but varied between N fertilizer levels and A. histrix intercropping with maize in this study. The positive response (increase) observed in this study for plant height, number of cobs per plot and cob length due to N application and intercropping with A. histrix could probably be due to incorporation of residues resulting in high SOC. Increase in soil organic matter level might have resulted in increase in soil fertility, nutrient supply, porosity, permeability and thus, soil productivity [17]. The findings obtained are consist ent with that of other workers in the same savanna agroecological zone of Nigeria [18]. Striga shoots per m -2 and per plot, and Striga reaction score generally were reduced by and varied between N fertilization and A. histrix intercropping with maize in this study. This clearly demonstrated that alternate plants of A. histrix could cause a reduction in Striga emergence, similar to application of N at 60 -120 kg N ha -1 . Furthermore, same hill intercropping of A. histrix also produced a reduction in Striga shoots in this study. These findings might be attributed to A. histrix acting as a trap or catch crop and the shading effect from A. histrix canopy. In addition to shading out Striga in intercropping systems, the A. histrix has also shown to stimulate the germination of Striga without acting as host, just like cowpea and soybean [6]; [14]; [9] and [19]. Striga shoots were generally low with application of 90 kg N ha -1 at 9 WAS, 90 kg N ha -1 and alternate hill planting at 12 WAS in 2012; 60 kg N ha -1 , 90 kg N ha -1 and alternate hill planting at 9 WAS, 60 kg N ha -1 was the case at 12 WAS in 2013. These demonstrate that alternate plants of A. histrix could cause a reduction in Striga emergence similar to application of N at 60 -90 kg N.This is in agreement with the findings of other workers. Usually large amounts of nitrogen are required to reduce Striga density [20]. However, improved growth and vigour due to N fertilization might have helped the maize crop to reduce Striga parasitism. [21] indicated higher Striga emergence without nitrogen compared with all nitrogen rates evaluated with sorghum. Early application of compound fertilizers might have depressed the germination of Striga seeds hence the delay in emergence [22]. Similarly, [19]; [23] and [24] observed that adequate urea and cereal legume rotation, have been reported to be effective in reducing Striga emergence and damage on maize and sorghum. Grain yield without inorganic N fertilizer was significantly lower than t hat of the other inorganic N levels. Similar responses to inorganic N fertilizer have been reported in the study area by [25]. The high yield obtained in the study area might be attributed to adequate moisture and other optimum growth factors obtained in t his study [26].

VI.
CONCLUSION Intercropping maize with A. histrix has the potential of reducing Striga parasitism with respect to Striga shoots per m -2 and plot, Strigareation score and enhancing maize grain yield. Both intercropping and N fertilization improved the soil organic matter and hence, reduced Striga infestation for good crop growth. Incorporation of the A. histrix residues substantially reduced Striga infestation. Maize intercropping with A. histrixwas as good as N fertilization, with respect to plant height, days to 50 % tasseling, number of cob per plot, cob length, 100 grain weight, stover and maize grain yields. There was response to inorganic N fertilizer application, suggesting the need for N application to maize for optimum grain yield. Nitrogen rate of 60 kg ha -1 was optimum for maize yield.