Response of African Nightshade ( Solanum sp . ) to cassava peel-based manure in the humid forest zone of Cameroon

Studies were conducted at Ekona in the humid forest agro-ecological zone of Cameroon to evaluate the effects of cassava peel-based manures on the growth and yield of African Nightshade. The first experiment consisted of evaluating the composted cassava peel and poultry manure applied at the rates of 0, 5, 10 and 20 t/ha and 150 kg/ha NPK (20:10:10) fertilizer. In the second experiment, a dried and grind mixture of cassava peel and poultry manure were applied at rates of 0, 5, 10 and 20 t/ha and 150 kg/ha NPK (20:10:10) fertilizer. Treatments were laid out in a randomized complete design and replicated three times. Growth and yield data were collected and subjected to analysis of variance (ANOVA). Significant treatments means were separated using students T test at p≤0.05. The different manures prepared were rich in macro nutrients particularly N (1-1.6%), P (0.7-1.4%) and K (1-1.7%). The experimental results showed that the applications of cassava peel-based manures significantly (p<0.05) influenced number of leaves, branches and biomass yield of African Nightshade. The use of cassava peel-based organic manure was very comparable to the use of inorganic fertilizer (NPK). Thus, cassava peel-based manure is promising for the enhancement of African Nightshade production, which could reduce the cost of fertilizer use and limit environmental pollution in Cameroon.


INTRODUCTION
There is increasing attention towards the use of organic wastes for soil fertility enhancement to boost food production without necessarily destroying the environment.This is because organic manures contain both macro and micro nutrients (Wang et al., 2016) and also improve soil structure, aeration, soil moisture holding capacity and water infiltration.
An increase in production and utilization of cassava has brought with it the release of huge quantities of wastes to the environment.Cassava peels are the major waste produced during cassava processing.This waste can be valorized as animal feed, used for the production of biodiesel as well as composted for other uses like mushroom substrate production and soil amendments (Iren et al., 2015;Sangodoyin and Amori, 2013).Studies by Iren et al. (2015) showed the nutrient composition of cassava peel to be: Organic carbon (12.57%), total nitrogen (1.47%), total phosphorus (0.79%), total potassium (0.11%), total calcium (1.89%), total magnesium (0.81%) and total sodium (0.012%).Based on this data, cassava peels are a potential alternative fertilizer source for the farmers which can be sold or used by the farmers for crop production.This will go a long way to improve the farmers' income, thus reducing poverty.
Consumption of traditional leafy vegetables in most of the developing countries is increasing due to their good adaptability to harsh climatic conditions and tolerance to pests and diseases, and also their nutritional and medicinal values (Prasad et al., 2008).One of the most commonly consumed traditional leafy vegetables in Cameroon is the African Nightshade (Kahane et al., 2005).African Nightshade grows in various soil types, but are best adapted to soils of high fertility; especially those rich in nitrogen, phosphorus and organic matter.
Some studies have shown that composting cassava peels eliminated the problem of waste disposal and increased the manure value of the materials (Adediran et al., 2003;Akanbi et al., 2007).Poultry manure is known to contain nutrient elements which can support crop production and enhance the physical and chemical properties of the soil (John et al., 2011).Although compost is increasingly becoming a suitable substitute for inorganic fertilizers to improve crop productivity, the information on the ideal cultural practices that enhance the quality of composts is scanty.It is a proven fact that the effectiveness of compost depends primarily on source and type of organic material, method of composting and compost maturity.Mature compost (finished compost) provides a stabilized form of organic matter.In effect, biofertilizers and soil conditioners have far greater values than just their macronutrient contents.These materials have a much greater residual effect on soil tilth and fertility than most chemical fertilizers because of the slowrelease character of their nitrogen and phosphorus components.Compost application improves the development of root systems, increases the diversity of root fungal flora, promotes the growth of plants, reduces the incidence of soil-borne diseases, and depresses the propagation of pathogens (Nitta, 1994).Thus, the aim of this study was to evaluate the effects of cassava peelbased manures on the growth and yield of African Nightshade.This study had as specific objectives to assess the mineral composition of cassava peel compost prepared following different approaches, and to determine their effects on growth and yield of African Nightshade.

Composting
Cassava peels were collected from water fufu (a local staple food from cassava) producers in Muea and Ekona areas of the South West Region of Cameroon.Poultry manure was bought from a poultry farm in Mamu Village and Pueraria phaseoloides harvested around the IRAD (Institute of Agricultural Research for Development) Ekona experimental fields.Cassava peel compost was prepared using two different recipes: Firstly cassava peel and poultry manure in the ratio of 3:1 (dry weight) and secondly using cassava peel, poultry manure and weed (P.phaseoloides) in the ratio of 3:1:1 (dry weight).These materials were combined in the said ratios and piled in heaps covering a surface area of 1 m 2 and height of 1.5 m.The weed was chopped into small pieces before usage.Two heaps were prepared using each of the recipes above with different turning frequencies: 1. Compost 1 (CP 1): Cassava peel and poultry manure (ratio 3:1) turned every two weeks; 2. Compost 2 (CP 2): Cassava peel and poultry manure (ratio 3:1) turned once a month; 3. Compost 3 (CP 3): Cassava peel, P. phaseoloides grass and poultry manure (ratio 3:1:1) turned every two weeks; 4. Compost 4 (CP 4): Cassava peel, P. phaseoloides grass and poultry manure (ratio 3:1:1) turned once a month; 5. Compost 5 (CP 5): Cassava peel only turned once a month; 6. Compost 6 (CP 6): Cassava peel and poultry manure (ratio 3:1) dried and grind without composting.
Cassava peel was combined with other local fertilizer sources such as poultry manure and P. phaseoloides to compare the nutritional value of CP 5 (cassava peel only) to that of cassava peel combinations with other fertilizers.
During the composting process, the temperatures in the different heaps were monitored every two weeks using a field thermometer.Watering was done twice for each heap during turning.The compost was matured by the end of the 12 th week and the temperature dropped and remained unchanged with the compost having no peculiar smell.
Dry cassava peel manure (CP 6) was prepared by drying cassava peels and poultry manure and mixing them in the ratio 3:1 for cassava peel and poultry manure respectively.This mixture was grind into fine particles using a shredder.
The different manures (fertilizers) obtained using the different procedures were analysed for their macro nutrient composition (nitrogen, phosphorus, potassium, calcium and magnesium as well as the pH) following standard procedures.Based on the results of the analysis and considering the N levels, the two best manures (fertilizers) were used to grow African Nightshade.The fertilizer rates were 0, 5, 10 and 20 t/ha for the manure and 150 kg/ha NPK (20:10:10) with treatment 1 (T1) = control, T2 = 5 t/ha, T3 = 10 t/ha, T4 = 20 t/ha and T5 = NPK (20:10:10) at 150 kg/ha.

Study area
Field experiments were carried out at IRAD Ekona.The Ekona site belongs to the humid forest zone with unimodal rainfall regime.This area is characterized by volcanic soils (andosol) and precipitation of 3,076 mm per year.The average air temperature varies from 19 to 23°C.It is governed by a "cameroonian" climate (very hot and  (Temegne et al., 2015a).

Soil sampling and analysis
A composite sample of the top soil (0-15 cm depth) was collected from the experimental site with an auger before bed preparation following the transect method described by Okalebo et al. (2002).About 200 g of the samples were analysed for physical and chemical properties in the IRAD soil laboratory of Nkolbisson (Cameroon).The soil sample was air-dried and ground to pass through a 2 mm sieve.For carbon (C) and nitrogen (N) analysis, the soil was further fine ground to pass through a 0.5 mm sieve.Soil pH in water, was determined in a 1:2.5 (w/v) soil: water suspension.Organic C was determined by chromic acid digestion and spectrophotometric analysis (Heanes, 1984).Total N determined from a wet acid digest and analysed by colorimetric analysis (Anderson and Ingram, 1993).P was extracted using Bray extractant and the resulting extract analysed using the molybdate blue procedure described by Murphy and Riley (1962).Exchangeable cations Ca, Mg, K and Na were extracted using the ammonium acetate (NH4OAC, pH: 7) and determined by flame atomic absorption spectrophotometry.Cation exchange capacity (CEC) was determined using ammonium acetate.Results of the soil physico-chemical properties are presented in Table 1.

Experimental layout
The experimental design was a randomized complete block design with three replicates.A land area of 10 m  10 m was ploughed and harrowed and mapped out into plots (blocks) and sub-plots (treatments).Each sub-plot measured 1.5 m  2 m with 1.5 m alley between plots and 0.5 m alley within each sub-plot.Thus each treatment measured 2 × 1.5 m.
To determine the moisture content in the compost, 100 g of the compost was oven dried at 80°C to constant weight and the amount of absorbed moisture contained in the compost determined as the difference between fresh weight and dry weight.Equivalent weights of 5, 10 and 20 t/ha of manure on dry weight basis were applied to designated plots on the field two weeks before planting (0, 1.5, 3 and 6 kg/subplot representing 0, 5, 10 and 20 t/ha).NPK (20:10:10) at 150 kg/ha (45 g/subplot) was applied to the designated plots three weeks after planting.
Seedlings of African Nightshade were planted at a spacing of 20×20 cm on slightly raised beds.Weeding and watering were done regularly.At five weeks after planting, five plants were tagged per plot and sampled for the following growth parameters: Plant height, leaf area, number of leaves and branches.Each plot was ratooned (at 10 cm above the soil level) for marketable yields assessments at the 6th and 10th weeks.The ratooned plants were allowed to regenerate, and four weeks later, the marketable yields were again re-assessed.

Data analysis
Data collected was subjected to an analysis of variance (ANOVA) and means separated with student t test at P < 0.05 using the JMP 5 SAS software (SAS, 2002).

Nutrient content of the prepared manures
The chemical composition of the different compost prepared is presented in Table 2.All pH values of the prepared composts were greater than 7, so they were basic.CP 2 presented the highest pH value while the lowest was obtained for CP 6 which is the dry fertilizer prepared by grinding a mixture of dry cassava peels and dry poultry manure in the ratio of 3:1.However, the difference was not significant.The pH obtained for these prepared compost manures was generally within the range of 7.5 to 8.5 recommended by USDA-NRCS (2000).
The highest level of nitrogen (1.63%) obtained for CP 6 dry manure compared to the other manures could be attributed to the fact that most of its nitrogen was not lost  during drying compared to the N loss during composting.This is in agreement with other studies which confirm nitrogen lost during composting (Liang et al., 2006).The lowest level of N in CP 5 is logical because no additional nitrogen source was added to the cassava peels during composting.The fact that only cassava peels were composted for CP 5 production could account for its lowest phosphorus level.The K, Ca and Mg levels for CP 5 were among the highest suggesting that cassava peels are quite rich in these elements.Comparing the values obtained from composted cassava peels and literature values of un-composted cassava peels showed that some values like N, P and Mg decreased during composting while K and Ca values increased.This increase was in agreement with the study of Iren et al. (2015).
Comparing compost 1 and 2, then 3 and 4 which had the same compositions but varied in the frequency of turning, there were no clear trends or significant differences between most chemical elements in the various composts.Although for nitrogen, there were lower N concentrations for composts that were turned once in a month (CP 2 and CP 4).This showed that more nitrogen was lost with less turning.This disagrees with the results of De Guardia et al. (2008), Körner and Stegmann (2003) and Liang et al. (2004) who found higher ammonia emissions with higher aeration rates.This difference could result from the reaction of the different nitrifying bacteria with aeration and the nature of the compost material (De Guardia et al., 2009).The results of this study therefore suggest that both frequencies of turning could be used with little effects on the properties of the finished compost.
It is worth noting that the composition of N, P and Mg obtained in this study was lower than the values obtained by Iren et al. (2015) who composted cassava peels and poultry manure in the ratio of 1:1.The pH (H 2 O), K and Ca levels were higher in this study than in the study by Iren et al. (2015).This difference could be attributed to differences in the proportions of the different components since the composting period was 12 weeks for both studies.

Influence of the different amendments on African Nightshade growth
Based on the N levels of the various manures, CP 1 (cassava + poultry manure at 3:1 and turned every two weeks) and CP 6 (dried and ground cassava peels and poultry manure at 3:1 without composting) were used to grow African Nightshade at different dosages known respectively as Experiments 1 and 2.

Growth parameters at five weeks after transplanting
As shown in Table 3, there were no significant differences in mean plant height, number of leaves, number of branches, leaf length and number of plant with flowers for the various treatments in Experiment 1. Leaf width however presented a significant difference with T2 having the highest mean leaf width.The plot treated with inorganic fertilizer had the lowest mean plant height.This could be attributed to the fact that the plants had not taken up most of the fertilizer applied since it was applied three weeks after transplanting and this measurement was done just two weeks after fertilizer application.Although plant height was lowest, T5 presented the highest number of leaves showing that most nutrients were used for leaf formation at the expense of height.
The control plot presented the lowest number of leaves, branches, leaf length and number of plants with flowers.This could be attributed to lack of adequate nutrients for growth and development.There was a significant difference between the different amendments with regards to the average leaf width.In most parameters, the organic amendments were very comparable to the inorganic fertilizer.
Considering results of the experiment carried out using ground dry cassava peels and poultry manure (Experiment 2), there were significant differences in the growth parameters at the fifth week after transplanting (Table 3), except for the average number of leaves, leaf length and number of plants with flowers.For plant height, leaf length and width, the plot treated with inorganic fertilizer (T5) presented the highest values while the plants in the control plot presented the lowest average plant height, number of branches and leaf length.
The experiment did not influence the growth parameters of African Nightshade (Table 3).

Growth parameters at six weeks after transplanting
At the sixth week after planting, in Experiment 1, there was no significant difference in most of the growth parameters with respect to the different amendments (Table 4).However, there were significant differences observed in the average number of leaves per plant and number of branches with the control treatment having the highest values.This suggests that at this time, during the experiment, the plots that were amended loose more nutrients to microbes during manure breakdown, which was not the case with the control.
In Experiment 2, growth parameters at the sixth week showed that there were no significant differences between the various treatments.For plant height and number of leaves, plants treated with organic manure at 10 t/ha (T3) presented the highest values (Table 4).The highest average number of branches (4.6) and flowers per plant (5) observed for the control treatment could be attributed to nutrient deficiency especially nitrogen.This is similar to the study of Wolf (1999) who explained that plants suffering from nitrogen deficiency mature earlier and their vegetative growth stage is shortened.
In this study, the various treatments did not influence the plant height, number of leaves and number of branches of African Nightshade at six weeks after planting (Table 4).However, the leaf length and the leaf width were significantly higher in Experiment 2 than Experiment 1.This suggested that composting would have resulted in loss of nutrients during the decomposition process and grinding of dried cassava peels conserved most nutrients.
Plant height increased with maturity, with maximum plant height of 35 cm recorded in this study.Solanum nigrum plant height of between 30.48 and 60.96 cm were reported by Millspaugh (1974) in his study and the results of the present study fall within this range.Edmonds and Chweya (1997) recorded 70 cm as the maximum height of S. nigrum in their study.Bvenura and Afolayan (2013) recorded a maximum height of 90.33 cm.These values are however higher than the values obtained in the present study.This could be attributed to the fact that records for plant height for this study ended at six weeks while the previous studies were much longer.Comparing results obtained from different parts of the world, different agro-ecological conditions presumably produce different plant heights of the same plant.Nitrogen generally stimulates vegetative growth (Zhang et al., 2010) meaning the formation of more buds and a subsequent increase in the number of leaves.From this study, it is obvious that as the height increased due to the uptake of N in its nitrate form, there was a general increase in vegetative growth as indicated by the increase in number of leaves with time.

Marketable yield
The marketable yields for the five plants sampled per plot at the 6 th and 10 th week after transplanting for experiment are presented in Table 5.This vegetable is usually marketed and consumed fresh, thus the total fresh weight for both harvests was calculated.The results showed that the control plot presented the lowest yields while the plot treated with the lowest quantity of manure (T2) presented the highest total fresh weight, but the difference was not statistically significant.This showed the beneficial effects of amendment in African Nightshade yields similar to the observation of Ondieki et al. (2011).The overall fresh weight for the compost amended plots was very similar to that of the plot treated with inorganic fertillizer.In addition, the work of Ngome et al. (2013), Mary and Nithiya (2015) and Temegne et al. (2015a, b) showed that the chemical composition of the soil affect the growth and plant yield.
In Experiment 2, yield data collected at the 6 th and 10 th week after transplanting showed no significant difference in the fresh weight of plants from the various amended plots.However, the plot treated with inorganic fertilizer (T5) had the highest fresh weight while the control treatment had the lowest fresh weight (Table 5).As concerns the dry weight, there were significant differences between treatments with the control treatment having the highest weight at the 6 th week and the plants treated with inorganic fertilizer (T5) having the highest dry weight at the 10 th week.The highest dry weight obtained for the control at the 6 th week suggested that the application of soil amendments increased plant water uptake which is lost during drying.The total fresh weight was highest for the plot amended with inorganic fertilizer.However, the values were very close to those obtained in organic manure amended plots.The control plot presented the lowest total fresh yield.This showed that amending the plots improved yield and this is in agreement with the results of Ondieki et al. (2011) who showed that compost manure improved yield of African Nightshade species.Tarla and Fontem (2010) obtained similar results on huckleberry (Solanum scabbrum) with poultry manure.
The mean fresh weight was better at 6 th than 10 th week after planting for both experiments.In fact, flowering took place 5 weeks after transplanting and most plant resources were mobilized for biomass production which would justify the higher fresh weight obtained at the 6 th week (Table 5).On the other hand, at 10 weeks after planting, the roots of the plant are depleted, the plant supply is reduced, and the leaves of the base quickly become senescent and fall.This last observation could justify the low fresh weight at the 10 th week.

Conclusion
Based on the N levels of the various manures, CP 1 (cassava + poultry manure at 3:1 and turned every two weeks) and CP 6 (dried and ground cassava peels and poultry manure at 3:1 without composting) were the best formulations.Using CP 6 gave better results than CP 1 for African Nightshade growth at six weeks after transplanting.The cassava peels based-manures prepared in this study were very comparable to other organic manures.The effects of the used organic fertilizers on African Nightshade growth and yield were very similar to that of inorganic fertilizer.This study has demonstrated that the use of cassava peels in the preparation of compost or as dry manure is promising in improving African Nightshade fresh yields.T2 (5 t/ha), T3 (10 t/ha) and T4 (20 t/ha) were the best compost doses.
The results of this study conclude that very high dosages of the organic manure are not very necessary since they do not improve yield or growth significantly.T2 can therefore be recommended for the cultivation of African Nightshade in the South-West Region of Cameroon.Thus using the organic fertilizers for crop production would be more economical and will also be very useful in the development of sustainable food production systems.This approach (use of organic fertilizer) will go a long way to promote environmental safety for waste will be converted to wealth.The cumulative agronomic and economic value of some organic materials applied to agricultural soils could be more than five times greater in the post-application period than the value realized during the year of application.Thus it is suggested for this study that, more significant effects of the amendments could be observed following studies on residual effects.

A
For each experiment, means with same letter in a column are not significantly different (p<0.05).

Table 1 .
Physico-chemical properties of the soil of the experimental site.

Table 2 .
Chemical composition of the different cassava peel-based manures.
humid), a variant of the equatorial climate

Table 3 .
Mean African Nightshade growth parameters as influenced by cassava and poultry manure-based compost at five weeks after planting.

Table 4 .
Mean African Nightshade growth parameters as influenced by cassava and poultry manure-based compost manure (Experiment 1) at the sixth week.
AFor each experiment, means with same letter in a column are not significantly different (p<0.05).

Table 5 .
Mean African Nightshade fresh weight as influenced by cassava and poultry manure-based compost at six and ten weeks after planting.For each experiment, means with same letter in a column are not significantly different (p<0.05). A