ARTICLE INFORMATION	ABSTRACT
Article history:  Received:26.07.2021 Accepted:24.09.2021 Published:31.10.2021  *Corresponding author: E-mail:   nweksoniyke@gmail.com Keywords:  Ash Crop production system  Intercrop  Mixed cropping  Multiple cropping  Residual yield	A two-year (2013 and 2014) field trial was conducted at the experimental farm of the Crop Science and Horticulture Department at Chukwuemeka Odumegwu Ojukwu University to study the residual effect of different fertility levels of rice mill ash on maize-soybean intercrop. In order to achieve the objective of the study, the experiment was arranged in a randomized complete block design  (RCBD) comprising of nine (9) treatments and three (3) replications.  The treatments were sole maize (SMO), sole soybean (SBO),  maize/soybean intercrop without application of rice mill ash  (IMBO), soybean + 10 t/ha rice mill ash (SB10), sole maize + 10 t/ha rice mill ash (SM10), maize – soybean intercrop + 10 t/ha rice mill ash (IMB10), sole maize + 20 t/ha rice mill ash (SM20); sole soybean  + 20 t/ha rice mill ash (SB20) and maize/soybean intercrop + 20 t/ha rice mill ash (IMB20). Data generated were subjected to analysis of variance of which the result of the study showed that for 2 years under study, incorporated rice mill ash (RMA) and intercropping system significantly increased the soil productivity, yield, and yield components of maize and soybean studied. The application of rice will ash at the rate of 20 t/ha competitively among other treatments increased fertility of the studied soil and the yield parameter assessed across the sole and intercrop. This however declined in the 2nd year (2014) result but the residual impact was strong though relatively alike and statistical equal for 10 t/ha and 20 t/ha  RMA results. The equivalent and relative yield of both maize and soybeans in the intercrop were found to be greatly influenced relative to their individual sole yield results. Findings from the study equally showed an intercrop advantage with land equivalent ratio  (LER) for the 2-year study ranged from 1.31 – 1.94 for the 2013-year planting and 1.81 -2.74 for the 2014-year planting. With this result, farmers within the area are encouraged to adopt this production system for soil productivity improvement and efficient land management.

INTRODUCTION 

The use of chemical fertilizer to replenish lost nutrient and sustain agricultural soils is very minimal in Nigeria and most of the African countries at large. The reason is that most farmers cannot afford the cost and the attendant problems such as unavailability at the point of need, soil acidity, nutrient imbalance, etc. In this contest, therefore, the management of wastes is very critical in keeping the agricultural soils supplied with essential plant nutrients for the healthy growth of crops.

Wastes are bound in urban cities and in mini and large agricultural processing industries but the problem is the policy articulation and adequate management of the wastes to ensure maximum benefits from them. When wastes are properly managed especially with referred to soil it becomes a  source of fertilizer that reduces the cost of production and the use of chemical fertilizer in crop production. It can also be used to reclaim degraded and marginal soils.

The good thing about soil is that it is a natural filter, thus an important medium for waste disposal. The essence of life on this planet earth depends largely on the sustainability of the soil. In all cases, man and animal depend on plants for life sustenance therefore the fertility status of any given soil should be paramount to farmers, as it is a measure of the availability of the nutrients to the plant in their right proportion and balance. The objective of intercropping is to produce more crop yield on a piece of land by making use of resources that otherwise would not have been utilized by a single crop.

This wonderful method of cropping if properly planned and implemented in Nigeria soils especially southeastern region soils taking into account the climate, crop type and variety, disease and pest, as Nweke  (2018) argued could be a panacea for sustainable food production, environmental harmony and a strong check to land degradation in the area.  

This new and improved method of cropping advocated has been avoided by farmers especially the large and commercial farmers on the pretense of complications of planting and harvesting. Nonetheless, intercropping usually give benefits from increased light interception, root contact with more soils and more nutrients, increased microbial activity, and can act as a deterrent to pests and weeds of the other crops.

Available growth resources such as light, water, and nutrients are more completely absorbed and converted to crop biomass by intercropping as a result of differences in competitive ability for growth factors between intercropping components (Nweke,  2018, 2020).

However, food production is based on the continuous availability of plant nutrients in the soil, continuous cropping without adequate input, and the depletion of soil nutrients with a resultant poor yield of cultivated crops.

With this trend soil nutrients that will boost crop growth and yield decline progressively unless the nutrients are replenished through organic wastes or chemical fertilizers. Soils and crops differ in their response to organic waste amendments and therefore important to investigate more closely the influence of these organic wastes on a range of crops and of soil physical, chemical, and biological properties. Thus, the objective of this study is to determine the residual effect of rice mill ash at different fertility levels on the maize soybean intercrop.  

MATERIALS AND METHODS 

The experiment was carried at the Teaching and  Research form of Crop Science and  Horticulture of Chukwuemeka Odumegwu  Ojukwu University, Igbariam Campus  Anambra State Nigeria, Between May and September 2013 and the 2014 planting season.  The area is located between the latitude 06  14 `N and longitude 06 45 `E and within the humid tropical rainforest zone characterized by both wet and dry seasons with high rainfall and high temperature.  

Land Preparation /Treatment Allocation  and Experimental Design  

The land area measuring 434 m² was manually cleared with cutlass and debris removed. The dominant weed species in the area before they were cleared were  Imperata cylindrical (spear glass), Talinum triangular (water leaf), Eleusine indica (crowfoot grass), and Aspila africana (wild marigold). The experiment was laid out in a  randomized complete block design (RCBD)  with 9 treatments.  

The treatments are as follow;  

Sole maize (SMo)  

Sole soybean (SBo)  

Maize-Soybean intercrop (IMBo) 

Sole maize treated with a 10 t/ha rice mill ash  (SM10)  

Sole soybean treated with 10 t/ha rice mill  ash (SB10)  

Maize-Soybean intercrop treated with 10  t/ha rice mill ash (IMB10) 

Sole maize treated with 20 t/ha rice mill ash  (SM20)  

Sole soybean treated with 20 t/ha rice mill  ash (SB20)  

Maize -soybean treated with 20 t/ha rice mill  ash (IMB20)  

The treatments were randomly assigned to each plot measuring 3 m x 4 m (12 m2) and adjacent plots were spaced at 0.5 m within each block and 1m between blocks. The treatments were replicated 3 times. Two seeds of maize and soybean were sown directly on their respective plots. Supply of non-germinated seeds was done two weeks after planting for maize and 28 days after planting for soybean. Weeding was done manually every other week with either hoes or hand pulling. The maize and soybean were harvested when they are matured and dried for their seed and grain yield.

The same procedures were followed in 2014 with the exception of the application of rice mill ash. Soil samples were collected from 0 – 25 cm depth randomly from the land area before cultivation and bulk together as a composite sample.

After harvest soil samples were collected from each plot at a depth of 0 – 25 cm. These soil samples were air dried and sieved with 2 mm mesh sieve and used to analyze selected soil chemical properties and core samples used for the analysis of selected physical properties of the soil. The analysis of both physical and chemical properties follow the method outlined in Black (1965) Agronomic parameters measured include; the number of nodules of which destructive sampling was used to determine the number of nodules at 10 weeks after planting using ten (10) randomly tagged plants that were uprooted, the weight of nodules, the weight of pods,  maize grain yields, and soybean seed yield  (t/ha).  

Relative yield of maize 

 

This was used to evaluate the yield of maize  expressed as sole crop and intercrop using  the equation; 

���� =^{��������} 

_{������}  

Where RY = Relative Yield, YIMB = Yield of  maize as intercrop in soybean  

YSM = Yield of maize as a sole crop.  

Relative yield of soybeans 

The yield of soybean expressed as sole crop  and intercrop using the equation; 

 ���� =^{��������} 

������ 

Where; RY =Relative yield, YISM = Yield of  soybean as intercrop in maize  

YSB = Yield of soybean as a sole crop  

Equivalent yield of maize and soybean   

This was done by calculating the total yield of maize grain as compared to soybean seed in t/ha. The following equations were used;  

������ = ������ + (^{������×����} 

_���� )

������ = ������ + (^{������×����} 

_���� )  

Where: 

EYS = Equivalent yield of soybean 

EYM = Equivalent yield of maize 

YSB= Yield of sole soybean 

YSM= Yield of sole maize 

YIM= Yield of maize in intercrop 

YIB= Yield of soybean in intercrop 

PM= Selling price of maize at the period of  study 

PB= Selling price of soybean at the period of  study 

Land equivalent ratio (LER) 

This tool was used to evaluate the intercrop  efficiency in yield to sole crop 

_{������ =}������ 

_{������ +}������ 

������ 

Where;  

LER = Land equivalent ratio 

YIM = Yield of maize in intercrop 

YSM = Yield of sole maize 

YIB = Yield of soybean in intercrop 

YSB = Yield of sole soybean 

Data analysis 

Data generated from the study was subjected to the analysis of variance test based on randomized complete block design  (RCBD) and treatment means were separated using the least significant difference at a 5% alpha level. 

RESULTS  

On farm observation  

The maize seed germinated within 4 – 5 days after sowing while the soybean germinated  14 days after planting. Pest attack was a  major problem, in the soybean plot amended with rice mill ash. It seems the ash attracted the pest as their effects declined in the 2014  planting year when ash was not applied. Flea flies and grasshopper was major pests while in the sole plots, these insects were not seen but maggot was noticed to eat the leaf of the plant which often lead to the death of the affected plant.

Another problem is the bush rat that dug up a hole and ate up the nodules of soybean, mostly observed in plots amended with 10 t/ha of rice mill ash. Soil erosion problem was partly observed but was controlled. On the whole, number of plants that survived to maturity was observed to be higher in sole cropping compared to intercropping. However, the above-numerated problems were drastically reduced in the second year of the planting season (2014).  

Initial soil properties 

The chemical characteristics of the studied soil indicated low levels in all the parameters tested, except for base saturation (BS) value and available P that is of moderate value  (Table 1). Nutrient content of rice mill ash before the  study. The properties of rice mill ash before application in Table 2 showed that the pH of the ash is strongly alkaline (11.40) however the ash contains lower levels of exchangeable bases, P, organic carbon (OC)  and total nitrogen (TN). Effect of different fertility levels of rice mill ash and intercrop system on the chemical properties of the studied soil.

The result of the chemical properties of the studied soil presented in Table 3 showed significant differences among the treatments in 2013 planting season except for the results of K, Na, EA, ECEC, and BS while the 2014  planting season result showed non-significant (P < 0.05) different among the treatments in all the parameters assessed except for pH, OC and BS.

Most of the parameters tested in 2013 and 2014 planting season showed increments in value as the  RMA levels increased. Also decreased values were recorded in the 2014 planting season relative to the 2013 planting season results in all the parameters assessed in the study. The  RMA increased the pH of the soil to alkaline in 2013 planting season but slightly acidic in the 2014 planting season. The residual effect of  RMA on the parameters were strong but relatively alike in value. Most of the values  obtained in the 2014 planting season from 10  

Table 1. Initial soil properties 

t/ha RMA and 20 t/ha RMA fertility levels were the same and statistically equal. The obtained values in the study were however higher in amended plots relative to the control plots though more pronounced in the 2013 planting season than 2014 planting season result. 

Parameter value 

Sand 770 gkg^-1 Silt 780 gkg^-1 Clay 152 gkg^-1 Textural class Sandy loam 

pHH2O 6.46 

Available P 26.10 mgkg^-1 Total N 0.126% 

OC 0.77% 

OM 1.32% 

Ca 5.60 cmolkg^-1 Mg 2.40 cmolkg^-1 K 0.118 cmolkg^-1 Na 0.096 cmolkg^-1 EA 0.40 cmolkg^-1 ECEC 8.614 cmolkg^-1 BS 95% 

Table 2 Chemical properties of rice mill ash before the commencement of the study 

Parameter Value 

pHH2O 11.4 

OC% 0.16 

N% 0.22 

P mgkg^-1 0.45 

Ca comlkg^-1 3.84 

Mg cmolkg^-1 1.28 

K cmolkg^-1 0.78 

Na cmolkg^-1 2.25 

Effect of different fertility levels and intercrop  system on the physical properties of the  studied soil 

The physical properties of the soil showed that apart from the % clay result the treatment differed significantly (P < 0.05) in the 2013 planting season (Table 4). But in the 2014  planting season, the particle size result indicated non-significant but showed a significant effect on the result of bulk density  (BD) and total porosity (TP).

The value of BD  decreased and TP increased with an incremental increase in RMA in the 2013 planting season while there was no particular order in the result in the 2014 planting season. However, the highest recorded values for BD and TP were from 10 t/ha RMA and 20 t/ha RMA  respectively.

There was a little bit decrease in the BD value of the 2013 planting season relative to the 2014 planting season while the 2014 planting showed increased TP value relative to the 2013 planting season result. The particle size data indicated increased constant sand and silt and decreased constant clay in the 2014  planting season compared to the obtained value of the parameters in the 2013 planting season. 

Table 3. Effect of different fertility levels of RMA on the chemical properties of the studied  soil 

Treat 

 2013 planting season 2014 planting season 

ment 

p 

H 

H2 O 

P 

mg kg 1 

N % 

O C 

% 

Ca Mg K Na  EA ECEC 

 Cmolkg^-1 

B 

S 

% 

p 

H 

H2 O 

P 

mg kg 1 

N  % 

O C 

% 

Ca Mg K Na  EA ECEC 

 Cmolkg^-1 

BS % 

Ot/ha RMA 

10t/ha RMA 

20t/ha RMA 

6. 

97 

7. 

47 

8. 

23 

15. 8 

21. 6 

28. 5 

0. 

06 

0. 

13 

0. 

24 

0. 

85 

1. 

01 

1. 

09 

3. 2 

4. 8 

5. 6 

1. 6 

2. 4 

2. 0 

0. 

13 

0. 

15 

0. 

23 

0. 

89 

0. 

12 

0. 

17 

0 . 

3 0 . 

4 0 . 

6 

5. 

34 

7. 

91 

8. 

56 

9 4 

9 5 

9 3 

6. 1 

5. 9 

5. 4 

20. 52 

20. 52 

21. 45 

0. 

07 

0. 

07 

0. 

04 

0. 

37 

0. 

46 

0. 

33 

2 . 

0 1 . 

8 2 . 

4 

i. 0 

1 . 

4 1 . 

0 

0. 

13 

0. 

13 

0. 

13 

0. 

08 

0. 

08 

0. 

06 

1 . 

8 1 . 

6 1 . 

0 

9 . 

6 9 . 

6 9 . 

6 

33. 44 

33. 52 

37. 40 

LSD 0.05 

0. 

47 

3.1 6 

0. 

29 

0. 

19 

1. 

34 

0. 

34 

N S 

N S 

N S 

2. 

35 

N S 

0. 

25 

NS N S 

0. 

37 

N S 

N S 

N S 

N S 

N S 

N S 

1.5 8 

RMA = Rice mill ash 

Table 4 Effect of different fertility levels of RMA on the physical properties of the studied  soil 

Treatment 2013 planting season 2014 planting season 

Sand % 

Silt % 

Clay % 

TC BD gcm^-3 

TP % 

Sand % 

Silt % 

Clay % 

TC BD gcm^-3 

TP % 

Ot/haRMA 78 6.50 15.2 LS 1.5 43 82 12 6 LS 1.38 47,92 10t/haRMA 74 5.50 15.2 LS 1.4 47 82 12 6 LS 1.45 45.28 20t/haRMA 80 4.80 15.2 LS 1.3 51 82 12 6 LS 1.21 54.34 LSD0.05 1.38 0.58 NS 0.09 2.87 NS NS NS 0.19 2.98 

RMA = Rice mill ash; TC =Textural class; BD = Bulk density; TP = Total porosity t/ha RMA and 20 t/ha RMA varied in their  

Effect of different fertility levels and intercrop system on maize grain, yield, soybean seed yield, pod yield (t/ha), and number of nodules and weight of nodules.  

The result presented in Table 5 showed a significant difference (P < 0.05) in all the parameter measured in both the 2013 and 2014  cropping season except for pod weight in the 2013 cropping season and the number of nodules in the 2014 cropping season. The sole maize (SMO) showed a higher in value (2.81  t/ha) compared to the intercropped maize  (IMBO), 2.64 t/ha. The plot was amended with 10 yield results. SM20 recorded the highest maize grain yield of 6.96 t/ha, this was closely followed by SM10, IMB20, and IMB10. Soybean seed yield and pod weight showed a result variation of SB20 > SB10 > SB0 > IMB20 > IMB10  > IMB0.

The highest number of nodules and weight of nodules were recorded in SB20 the next in rank is SB10 for the two parameters.  No value was recorded for these two parameters in SB0 and IMB0. For the 2014  cropping season the trend of the result was almost the same with the 2013 planting season results. The highest maize grain yield was recorded in IMB10, the next in rank was SM10 and the least value of 0.72 t/ha obtain from SM20. IMBO recorded the least soybean seed and pod weight yield of 0.04 t/ha and  0.09 t/ha of which is 84.62% and 84.15%  respectively decrease in value relative to  IMB10 recorded the highest (0.26 t/ha  and 0.59 t/ha) of soybean seed and pod weight respectively.

The result obtained from SB10, IMB10, SB20 and IMB20 showed statistically similar result for the two parameters. SB20 and IMB20 recorded the same value for the number of nodules with the highest value of 26.30 recorded by  IMB10. The least value weight of nodules was obtained from IMB0 as against the highest value of 1.55 g recorded in IMB10. In all the parameters the values obtained in the first planting season (2013), showed higher values compared to the values recorded in the second planting season (2014). 

Table 5: Effect of different fertility level and intercrop system on maize grain yield, soya  bean seed, pod yield (t/ha), number of nodules and weight of nodules.  

Treatme 

2013 Planting Season 2014 Planting Season 

nt 

SM₀: SB0 IMB0 

SM₁₀:SB 10 

IMB10 

SM₂₀:SB 20 

IMB20 

LSD 0.05 

Maize  grain  (t/ha) 

2.81 

2.64 

5.94 

4.94 

6.96 

5.25 

1.62 

Soya  bean  seed  (t/ha) 

0.40 

0.22 

0.68 

0.30 

1.06 

0.38 

0.60 

Pod  

yield  (t/ha) 

0.56 

0.44 

0.96 

0.47 

1.39 

0.49 

NS 

No.  of  

nod ules 0 

0 

36.0 10.3 79.8 13.7 

15.4 7 

Weight  of  

nodule s 

0 

0 

1.50 

1.33 

3.65 

1.31 

0.85 

Treat ment 

0.79 1.14 1.67 2.24 0.72 1.43 0.74 

Maiz e  

grain  (t/ha) 0.11 

0.04 

0.21 

0.26 

0.24 

0.18 

0.15 

Soya  bean  seed  (t/ha) 

0.25 

0.09 

0.54 

0.59 

0.50 

0.46 

0.23 

Pod  yield (t/ha ) 

11.0 9.0 

13.0 26.3 11.0 11.0 NS 

No. of  nodules 

0.79 

0.37 

0.90 

1.55 

0.50 

0.55 

NS 

Effect of different fertility levels of rice mill  ash and intercrop system on equivalent and  relative yield of maize and soybean and land  equivalent ratio.  

The equivalent yield result for maize and soybean showed an order 20 t/ha RMA > 10  t/ha RMA > 0 t/ha RMA (Table 6). The 0 t/ha  RMA recorded the highest value in relative yield (0.95 t/ha) for maize and for soybean 20  t/ha RMA gave the highest of 0.52 t/ha, while  0.10 t/ha was the least value for relative yield of soybean was obtained from 0 t/ha  RMA.

The land equivalent ratio showed a resulting scenario of 0 t/ha RMA > 10 t/ha RMA > 20 t/ha RMA. In the 2014-year planting season, the equivalent yield of maize and soybean indicated 10 t/ha RMA > 20 t/ha  RMA > 0 t/ha RMA. The relative yield result for maize and soybean depicted 20 t/ha RMA  and 10 t/ha RMA to have recorded the highest value of 1.98 t/ha and 1.24 t/ha respectively.

While the land equivalent ratio showed an order of 20 t/ha RMA > 10 t/ha  RMA > 0 t/ha RMA. The two seasons under study (2013 and 2014 season) varied greatly in the results generated and there was no consistent order in the value recorded for the parameters apart from the equivalent yield value of the first planting season. The relative yield of maize and soybean and land equivalent ratio  (LER) result of the 2014 planting season showed an increased value relative to the 2013  planting season result.

The percentage increase in relative yield of maize and soybean in the 2014 planting season relative to the 2013 planting season were; 34.03%, 38.06%,  60.61%, and 72.22%, 60.48%, 30.67% for 0  t/ha RMA, 10 t/ha RMA and 20 t/ha RMA  respectively.  

Table 6: Effect of different fertility levels of rice mill ash and intercrop system on equivalent  yield of maize and soybean and land equivalent ratio. 

Treat 

2013 planting season 2014 planting season 

ment 

Equivalent  yield 

Relative Yield LER Equivalent  yield 

Relative Yield LER 

Maize Soya  bean 

Maize Soya  bean 

Maize Soya  bean 

Maize Soya  bean 

0t/ha  RMA 

10t/ ha  RMA 

20t/ha  RMA 

1.38 3.95 0.95 0.10 1.94 0.87 0.68 1.44 0.36 1.81 1.86 7.39 0.83 0.49 1.32 2.19 1.33 1.34 1.24 2.58 2.32 7.89 0.78 0.52 1.31 1.08 0.96 1.98 0.75 2.74  

DISCUSSION 

The soil analysis taken before the commencement of the study is evidence that the soil is deficient in plant nutrients as the parameters assessed were low except for available P that showed moderate level and high BS. The low-level value simply suggests that the soil is leached and strongly weathered resulting from high-temperature rain fall and rapid OM mineralization.  Hence required to be ameliorated for efficient production. The reduction in value obtained for the parameters in the 2014 planting season compared to the 2013 planting season may be due to none addition of RMA in the  2014 planting season.

While different in values may be attributed to differences in the nutrient content in the rates of RMA applied.  The rise in soil pH of the amended relative to the control plots may be due to microbial decarboxylation of the RMA that releases certain exchangeable bases into the soil solution. Thus, increasing the pH level of the soil and nutrient availability to the crop plants led to increased yield recorded in the study.

The low value recorded for chemical parameters assessed in the 2014  planting period compared to their relative value in 2013 year may be attributed to any or combination of the following factors;  residual effect of 2013 planting season, none application of RMA, uptake of nutrients by the crops, high productivity and reduced decomposition of organic matter. The addition of RMA was observed to reduce the  BD and increased the TP of the studied soil.  This is very critical as the parameters ensures easy root penetration, development, and proliferation as well as contain the required  O2 and water for soil microbes to survive in the soil.  

The significant difference effect recorded in the maize grain yield and soybean seed yield indicated that the intercropping system is positive and effective. However, the number of nodules and weight of nodules had zero value recorded and non-significant effect on pod yield in the 2013 planting year as as number of nodules and weight of nodules in the 2014  planting year could be due to competition of light energy and chemical nutrients making the intercropping system not to be efficient on the 3 parameters.

The shedding of soybean, disease pest, and bush rat attack as explained in the on-farm observation may also have influenced the recorded results.  The yield of maize and soybean was found to be increased in amended plots relative to the control plots, both 2013- and 2014-year  planting. Significant different observed suggest a higher content of nutrients due to the enrichment of the amended soil with OM by the rice mill ash. This increased the soil’s ability to absorb and retain water and plant nutrient elements required for optimal plant growth and yield recorded in this study.

The differences in values recorded could suggest differences in nutrient content and availability status in the type and rate of waste used. The 2014-year planting result values appeared to be reduced relative to  2013 planting in assessed parameters. This could be as a result of the non-application of rice mill ash in the 2014 year of crop production. Nonetheless, the rice mill ash and intercropping system showed a strong residual effect on the maize production,  number of nodules, and weight of nodules of which the greatest recorded value was observed in IMB10. The implication of the result is that without further application of the rice mill ash, reasonable yield of maize can still be obtained.

The pod yield result showed  non-significant effect of soybean intercropped with maize with considerable reduction in pod yield in intercrop relative to  sole and amended crop of which quantitatively the plot amended with 10 t/ha  RMA gave the highest value. The observed significant difference in grain and seed yield result in both 2013- and 2014-year planting attest to the evidence that intercropping system and RMA influenced the assessed parameters. The equivalent yield result was found to be increased with level of rice mill  ash in the 2013 planting season this might be  due to higher nutrient content in the level of rice mill ash applied. The 2014 planting season result however did not follow the same order and 10 t/ha showed strong residual effect among the other treatments. 

This might as well be due to different in the  rate of decomposition of rice mill ash and nutrient release ability in the form required for the crop as well as competition among the crops in picking up the released nutrients. The findings are in line with the reports of Odiete et al. (2005), and Mutuo et al. (2000) who reported that the rate of application of ash increased yield and that plot received organic biomass had a higher residual effect and gave 15% yield increase above the control. The observed reduction in the value of the maize and soybean by virtue of their equivalent yield recorded might have been influenced by both external and internal factors.

The external factor probably  might be due to the selling price of the product at the conclusion of the study. On  the internal factor, probably may be attributed to the disproportionality in  balance in soil nutrient. When optimum ratio  of bases exit in soil biological activity is increased of which will lead to more release of plant nutrients. Plant growing on such soil  will be balanced in mineral levels. 

Nonetheless the result obtained showed that the study was very profitable as it agrees with findings of Bhagat et al. (2005) who recorded the lowest net returns under sole groundnut compared to intercrop in a study of groundnut/sweet corn intercropping at different fertility levels and row proportions.  Also, in two (2) year study involving the performance of different hybrid maize varieties under an intercropping system with groundnut, Alom et al. (2009) made similar remark.

The relative yield of maize and soybean was observed to have decreased in the 2013 planting season relative to the 2014  planting season. This probably indicate that the effect of intercropping was more effective in the 2014-year planting compared to the 2013-year planting. The general growth patterns of crops in intercropping suggest that the main factor responsible for the advantages is that the use of early resources by growing soybeans complements the use of late resources by the longer-season maize crop. Regardless of the intercrop yield parameters, the LER result showed the intercropping system to be positive,  beneficial, and advantage.  

CONCLUSION  

Intercropping system and soil application of  rice mill ash have shown to have significant effect on the soil parameters studied, yield of maize and soybean. An alternative to use of chemical fertilizer and pesticide. The rice mill ash at the rate of 20 t/ha performed better both in sole cropping and intercropping though its effect on yield declined in the 2014 planting season.

The study confirmed that the way to achieve the aim of using organic waste to enhance the fertility status of soil is to apply them to the soil in the right quantity and quality to match nutrient release and needs for crops. The yield of soybean is an added advantage that will complement any loss in yield of maize. Hence, the farmers in  the locality are advised to embrace this package for effective crop production and zero tolerance of chemical inputs in the area. 

ACKNOWLEDGEMENT

The authors wish to express their thanks and appreciation to the staff of the Soil Science  Laboratory of the University of Nigeria Nsukka and Ebonyi State University Abakaliki, Nigeria for their assistance in the soil analysis of this work. We equally appreciate the effort of the co-authors Maduekwe, C. C. and Aniamalu, J.  M. I. who generated most of the data used in this work. Thank you all.  

REFERENCE 

Alom, M. S.; Paul, N. K.; Quayyum, M. A.  Performance of different hybrid maize  (Zea mays L.) and varieties under an intercropping system with groundnut  (Arachis hypogeae L.). Bangladesh J.  Agron. Res. 2009, 34-94: 585-595. 

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