EFFECTS OF DECAYING LEAF LITTER AND INORGANIC FERTILIZER ON GROWTH AND DEVELOPMENT OF MAIZE ( ZEA MAYS L . )

The effects of decaying leaf litter of Tithonia diversifolia and Vernonia amygdalina as organic fertilizer, inorganic fertilizer (NPK 15-15-15) and their combination effects on the growth and development of maize were studied in a screen house. Twenty-four experimental bags filled with 20 kg of loamy soil were laid out in a completely randomized design with six treatments and four replications for each treatment which included: 250 g of decaying leaves of T. diversifolia as mulch (T1), 250 g of decaying leaves of V. amygdalina (T2), 1.52 g of NPK (inorganic) fertilizer (T3), a mixture of 250 g of decaying leaves of T. diversifolia and 1.52 g of NPK 15-15-15 fertilizer (T4), a mixture of V. amygdalina and 1.52 g of NPK 15-15-15 fertilizer (T5) and control (T6). The significant growth as well as maize yields were obtained from T3 treated maize seedlings, and this was closely followed by T4 treated seedlings. The study showed that the decaying leaf litter as an organic fertilizer in maize production in a screen house conditions did not give better yield than NPK treatment alone.


Introduction
Maize (Zea mays L.) is one of the important staple and consumed food crops in the Sub-Saharan Africa.Despite the fact that Nigeria is one of the largest maize producers in Africa with about 9.4 million tons in 2012 (FAOSTAT, 2014), the country was still a net importer of this commodity as in 2010 (Cadoni and Angelucci, 2013).There has been a great increase in the demand for maize following the Federal Government of Nigeria's ban on importation of some food crops.This led to an increase in the rate of consumption of local maize with a corresponding increase in local maize production in recent years (FAOSTAT, 2014).However, this increase in production shows no correlation with yields in terms of hectograms produced per hectare as local yields have been fluctuating (FAOSTAT, 2014).There is therefore the need to ensure sustained maize production in order to meet its numerous demands (Iken and Amusa, 2004).
Several studies have shown that essential plant nutrients are below recommended levels in most Nigerian arable lands (Molindo, 2009;Jamala et al., 2012;Obidiebube et al., 2012;Ojeniyi et al., 2012).This perennial problem contributes immensely to factors that militate against food production.In fact, many reports have associated drastic decreases in maize yields with depleted soil nutrients (Ayoola, 2011;Zafar et al., 2011).The use of inorganic fertilizers has thus become a common practice as these agrochemicals help in improving soil fertility considerably.However, subsistence farmers do not have access to these products due to economic constraints.Similarly, the long-term consequences associated with disproportionate usages of synthetic fertilizers are sometimes catastrophic.
Organic fertilizers have proved to be a good solution to replenishing poor soils as they have been widely reported to increase soil organic matter, enhance other soil chemical and physical properties and are environment friendly (Efthimiadou et al., 2010;Ibrahim and Fadni, 2013).A wide array of organic materials such as animal manure, green manures, legume cover crops, and crop residues have been in use over the years and have been found to enhance crop yields and nutritional values compared to synthetic fertilizers (Ogbonna et al., 2012).However, organic manures from both plant and animal sources are not without shortcomings as they are not always readily available, and may require the extra cost and labour while acquiring them and are often needed in enormous quantities to produce noticeable effects (Adeoye et al., 2008;Ayoola, 2011).A better approach to soil fertility management consists of using balanced proportions of organic and inorganic fertilizers (Nziguheba et al., 2002).Efthimiadou et al. (2009) and Zerihun et al. (2013) have shown that an integrated use of organic and inorganic fertilizers improves crop growth and yield by enhancing several growth parameters including leaf area index, plant height, and grain yield of maize among others.Further studies have demonstrated that a combination of inorganic and organic fertilizers in the right amounts and proportions gives better results compared to when they are used solely (Ojeniyi et al., 2012).It has been reported that green manures when used in combination with inorganic fertilizers enhance crop and soil productivity (Kumar et al., 2000;Islam and Munda, 2012).The yields of important crops such as maize, cowpea, cassava and tomatoes and the soil on which these plants were grown have been found to be significantly improved under combined use of organo-mineral fertilizers (Taura and Fatima, 2008;Achieng et al., 2010;Ibrahim and Fadni, 2013).Furthermore, a lot of plant-based organic fertilizers have been reported to be beneficial to farmers.Tithonia diversifolia is a common invasive weed in Africa and Nigeria in particular (Akobundu and Agyakwa, 1998) and its biomass is rich in essential nutrients (Jama et al., 2000;Olabode et al., 2007).It has been used to increase the growth and yield of crops (Olabode et al., 2007;Ilori et al., 2010;Ademiluyi, 2012).
This study was therefore designed to assess the suitability of the decaying leaf litter of T. diversifolia and V. amygdalina as an organic fertilizer as well as NPK (inorganic fertilizer) and their combination effects on the growth and development of maize.

Material and Methods
The study was carried out in the screen house of the Department of Botany, University of Ibadan, Ibadan, Oyo State, Nigeria.The area lies between latitude 3.53°E and 7.26°N, and altitude of 185 m above sea level (Akin-Oriola, 2003;Chukwuka and Uka, 2007) with a mean daily temperature of 24.6°C.Twenty-four experimental bags perforated at the base, containing 20 kg of loamy soil were laid out in a completely randomized design with six treatments and four replications.The treatments included: 250 g of decaying leaves of Tithonia diversifolia (Ti) as mulch (T 1 ), 250 g of decaying leaves of Vernonia amygdalina (Ve) as mulch (T 2 ), 1.52 g of NPK (inorganic) fertilizer (T 3 ), a mixture of 250 g of decaying leaves of T. diversifolia and 1.52 g of NPK 15-15-15 fertilizer (T 4 ), a mixture of V. amygdalina and 1.52 g of NPK 15-15-15 fertilizer (T 5 ) and control (T 6 ) which did not receive any leaf litter or NPK.Each of the treatments received 5 seeds of maize downy mildew resistant variety also known locally as 'Oba super' and was regularly watered with about one litre volume of water at alternate day interval.The experimental soil samples were analyzed for nutrient status prior to the experiment for their physical and chemical properties.The results of the soil analysis are as shown in Table 1.Four weeks after sowing (4 WAS) the experimental bags were thinned down to one seedling per bag and treatment.The growth parameters such as leaf breadth, leaf length and plant height were measured with a metre rule, while the stem girth was taken using a Mitutoyo digitmatic electronic calliper (MDEC) Model Cd-8"P.These measurements were taken on a weekly basis for eight weeks.The maize was harvested 3 months after planting.The dry weight (yield) was taken after harvest and drying was done at a temperature of 70°C for 48 hours, and allowed to cool inside the oven, with the aid of a digital weighing balance.All the data obtained during the experiment were subjected to descriptive statistics and Duncan's multiple range test (p≤0.05)was used to separate the means using the statistical programme SPSS V.16 (SPSS Inc., Chicago, IL, USA).

Results and Discussion
Table 2 shows the effects of each of the treatments on the plant height.There was an increase in plant height with age in all the treatments.On a weekly basis, it was observed that there were no significant treatment effects (p≤0.05) on the plant height among the treatments in week 4, 6, 7, 8, 9 , 10 and 11 after sowing, except at the fifth week after sowing where the highest plant height was observed in T 4 (72.75±1.31cm), T 6 (72.75±1.89cm), and T 3 (72.25±1.11cm) and these were found to be significantly higher than T 5 (72.25±1.80cm), T 1 (69.25±0.48cm), and T 2 (68.25±0.85cm) respectively.As shown in Table 2, there was a rapid growth and development between the fifth week after sowing (5 WAS) and the eighth week after sowing (8 WAS).At this stage, the seedlings are passing through the logarithmic phase of growth, after which their growth is stabilized (stationary phase) leading to the death phase.Between these weeks, the tissues of the maize plants were still soft and tender, which made them able to obtain as much nutrients and water as possible from the soil aiding their rapid growth and development.After 8 WAS, the plants were stabilized in height, and there were no significant effects of the treatments.However, T 4 group gave the highest mean plant height, followed by T 3 and then T 6 (control).It was not surprising that T 4 ranked first.This may be due to the combining effects of both organic and inorganic fertilizers.T 3 maize seedlings did well because NPK is only a chemical that does not need microbial degradation before it would dissolve to release its nutrients unlike T. diversifolia which is organic manure.Likewise, the volume of water used to wet the plants was enough to make the T 4 seedlings thrive better.Achieng et al. (2001) reported similar findings in maize plant height in a maize field treated with T. diversifolia.Groups treated with the decaying leaf litter of Vernonia amygdalina (T 2 ) and the one containing its mixture with NPK (T 5 ) gave the poorest performance.This means that T 2 and T 5 do not really have significant effects on the height of maize plant.However, at 4-5 WAS, treatments with the decaying leaf litter of V. amygdalina were poor in height compared to other treatments.This is also in line with the work of Liasu and Achakzai (2007).They reported that tomato plants subjected to mulching and fertilization with T. diversifolia exhibited the highest plant height and number of leaves per plant when compared with other treatment combinations.Ademiluyi and Omotoso (2004) also reported that early maize growth rates in terms of height were better in soils treated with T. diversifolia than in soils treated with NPK fertilizers.T 1 = T. diversifolia; T 2 = V. amygdalina; T 3 = NPK; T 4 = NPK + T. diversifolia, T 5 = NPK + V. amygdalina, T 6 = Control.WAS = Weeks after sowing.Mean ± SEM (n = 4).The columns with the same letter are not significantly different at p ≤ 0.05 using Duncan's multiple range test.
Table 3 shows the effects of each of the treatments applied on the maize stem girth.The treatments showed significant effects on stem girth at 4 WAS and 8 WAS.The treatments were not significantly different from one another in all other weeks.At 4 WAS, T 3 was observed to give the highest stem girth (6.90±0.21mm) and this was followed by T 6 (6.60±0.18mm) and then T 4 (6.31±0.36mm).The lowest stem girth at 4 WAS was recorded in T 5 (6.09±0.21mm).At 8 WAS however, the highest stem girth was still recorded in T 4 groups (12.08±0.30mm), while the lowest stem girth was found in T 1 (10.23±1.17mm).The group treated with NPK fertilizer (T 3 ) gave the best performance with respect to the stem girth followed by the control group (T 6 ) and then those treated with NPK + Ti (T 4 ).It was observed that the group treated with decaying leaf litter of V. amygdalina alone (T 5 ) showed some surprising growth in girth of maize plant when used as mulch.Other treatments were not significantly different from one another.This study disagreed with Ademiluyi and Omotoso (2004), who reported that stem girth was better in soils treated with T. diversifolia than in soils treated with NPK fertilizers.T 1 = T. diversifolia; T 2 = V. amygdalina; T 3 = NPK; T 4 = NPK + T. diversifolia, T 5 = NPK + V. amygdalina, T 6 = Control.WAS = Weeks after sowing.Mean ± SEM (n = 4).The columns with the same letter are not significantly different at p ≤ 0.05 using Duncan's multiple range test.
Table 4 shows the effects of treatments applied on the leaf length.All the treatments were not significantly different from one another in all the weeks, except at 6 WAS and 10 WAS, where the highest leaf length was observed in T 3 (77.25±5.02cm) and T 5 (92.50±4.33 cm) respectively and the lowest leaf length was found in T 6 (64.25±4.52 cm) and T 1 (81.75±3.12cm) respectively.Decaying leaf litter of V. amygdalina with NPK fertilizer (T 5 ) had more positive influence on the development of maize leaf length.The group treated with NPK (T 3 ) gave the best results with respect to leaf length and followed by NPK + Ve (T 5 ).Treatments with NPK + Ti (T 4 ) including those treated with T. diversifolia alone (T 1 ) did not have a significant influence on maize leaf length.
Table 5 shows the effects of treatments applied on the leaf breadth.There was a progressive increase in the leaf breadth across all the treatments applied as the weeks progressed.At 4 WAS, the highest leaf breadth of (2.53±0.03cm) was observed in T 6 , and this was found to be significantly higher compared to other treatments.At 5 WAS, T 3 gave the highest leaf breadth of (3.63±0.06cm) while the lowest was recorded in T 1 (3.05±0.03cm).At 6, 7, 9, 10 and 11 WAS, the treatments showed no significant effect on the leaf breadth in all the groups, except at week 8, where the highest leaf breadth (5.30±0.12cm) was recorded in T 2 and which was found to be significantly higher compared to T 1 , T 3 , T 4 , T 5 and T 6 .Table 6 shows the effects of treatments applied on the maize cob dry weight.It was observed that the cob dry weight of T 3 groups (36.13±0.63g) was significantly higher compared to other treatments.This was closely followed by T 4 (34.13±0.59g).The lowest dry weight of cobs was however recorded in T 5 (32.13±1.06g).The result obtained for the mean dry weight of cobs is similar to that of the plant height.T 3 and T 4 seedlings gave the best yield with respect to dry weight of cobs.This is in consonance with the work of Achieng et al. (2001), who reported that T. diversifolia and NPK treatments were not significantly different for cob yield.The result of this study agrees with that of Ademiluyi and Omotoso (2004), who reported that there was higher vegetative and reproductive growth of maize in soils treated with T. diversifolia.Maize cob and grain yields were more increased by T. diversifolia biomass than by NPK fertilizer.

Conclusion
NPK treatment gave the best result in terms of the growth and development of maize.This was closely followed by T. diversifolia + NPK treatment.Therefore, it can be concluded that degraded soils could be recovered for crop production at low cost with T. diversifolia rather than with the high cost of NPK fertilizer.It can be also concluded that the decaying leaf litter of V. amygdalina could positively influence the leaf breadth development in maize.However, considering the cost of inorganic fertilizer, a combination of T. diversifolia and NPK fertilizers will be a wise strategy in soil fertility restoration.

Table 1 .
Physico-chemical properties of the soil.

Table 2 .
Effects of treatments on plant height (cm).

Table 3 .
Effects of treatments on stem girth (mm).

Table 4 .
Effects of treatments on leaf length (cm).

Table 5 .
Effects of treatments on leaf breadth (cm).

Table 6 .
Effects of treatments on yield of maize.