Soil chemical properties and growth response of Moringa oleifera to different sources and rates of organic and NPK fertilizers

The need for increasing production of Moringa oleifera in Nigeria can be achieved through adequate fertilization. This study investigated the effects of sources and rates of NPK (15:15:15) and compost on soil properties and productivity of Moringa at National Horticultural Research Institute, Ibadan, Nigeria. NPK was applied at 30, 60, and 90 kg N/ ha, cow dung (CD), poultry manure (PM) and organomineral (OM) were applied at 10, 20 and 30 tons/ha. The experimental design was a randomized complete block design with three replicates. Organic fertilizers were incorporated into the soil 2 weeks before sowing; NPK was split applied at 2 and 5 weeks after sowing. Seeds were sown at 75 cm × 75 cm spacing. Data were taken on plant height (cm), stem girth (cm), number of leaves, leaf biomass, stems weight and post-planting soil properties. Growth values for NPK and compost treatments were higher than the control. PM applied at 30 tons ha−1 resulted in highest growth values: plant height (65.91 cm), stem girth (1.51 cm) and number of leaves (14.20). PM applied at 30 tons ha−1 gave higher stem weight (2249.9 g) and leaf biomass (3610.5 g). Post-planting soil analysis indicated that nitrogen, phosphorus, calcium, sodium, manganese, iron and zinc contents were higher in plots with organic and inorganic fertilizers except for potassium and magnesium. PM proved more superior to CD manure and others because it produced better growth attributes such as shoot height, stem girth and number of leaves and leaf biomass than its counterparts produced.


Introduction
Moringa oleifera, also known as horseradish tree, is a medium-sized tree belonging to the family Moringaceae; it is adapted to a wide range of soil types, but grows best in well-drained loam to clay loam, neutral to slightly acidic soils, but cannot withstand prolonged water logging. It grows where temperature ranges from 26 to 40°C and annual rainfall totals at least 500 mm.
Interest in Moringa in recent times is skewed towards its medicinal properties. Hence, researchers focus on its value as medicine. Consequently, the demand for the plant products has been on ascendancy (Imoro et al. 2012). However, not much research has been done on its cultivation and fertilization in Nigeria with respect to its growth and productivity using different types of inorganic and organic manures commonly used by local farmers and more so, until recently M. oleifera was not popular in southwestern Nigeria despite its acclaimed economic and health importance (Odeyinka et al. 2007); hence, very little research has been done on the species, although it is widely used by the rural poor as a food resource.
Note This research was carried out in the southwestern part of Nigeria, where before now M. oleifera was not a popular field crop.
Nigeria is among countries with low to medium productivity soils (Eswaram et al. 1997) and are classified as being generally infertile (Aduayi et al. 2002), thus, necessitating the addition of fertilizers for optimum yield. Amelioration of soil by the use of inorganic or organic fertilizers is considered as a component of intervention for increased crop production around the world (Chand et al. 2006). The positive effects of organic manures on soil structure, aggregate stability, water-holding capacity and crop yield were reported in several studies (Togun and Akanbi 2003;Jedidi et al. 2004;Odlare et al. 2008). Low cost and ready availability of materials for their preparation, gradual release of plant nutrients, aeration, the ability of the soil to hold nutrients and being environmental friendly have made organic fertilizers popular among farmers.
This experiment was carried out to investigate the effects of different sources and rates of organic and inorganic fertilizers on early growth of M. oleifera and soil characteristics.

Materials and methods
Field experiments were carried out at the National Horticultural Research Institute (3°54 0 E, 7°30 0 N, and 213 m above sea level), Ibadan, to determine the optimum rate at which different rates and sources of fertilizers can be applied to soil to increase its productivity and growth of M. oleifera. The experiment comprises thirteen treatments: NPK (15:15:15) applied at 30, 60 and 90 kg N ha -1 , cow dung (10, 20 and 30 tons ha -1 ), poultry manure (10, 20 and 30 tons ha -1 ) and organomineral (10, 20 and 30 tons ha -1 ) along with the control. The experimental design was a randomized complete block design (RCBD) with three replicates. Organic fertilizers (poultry manure and cow dung) were incorporated into the soil 2 weeks before planting to allow for their mineralization, while NPK fertilizer was split applied at 2 and 5 weeks after planting while organominerals were applied at 2 weeks after planting to enable the seedlings absorb the mineral nutrients. Three seeds were directly sown per hole at 75 cm 9 75 cm spacing, on plots of size 9 m 2 . The seedlings were thinned to one plant per stand at 2 weeks after sowing (2WAS). Data on growth parameters (plant height, stem girth and number of leaves) were taken fortnightly from 4WAS for ten (10) weeks. Also leaf biomass was determined by cutting four stands per plot at 1 m above ground level; the pruned shoot were separated into leaves and stems, air dried at room temperature until uniform weight was achieved. This process was repeated every fortnight and the total sum of the leaf weight over time was recorded as leaf biomass. Samples of soil from each plot were taken before and 14WAS for laboratory analysis to determine the effects of treatments on soil properties. The soil samples were air dried, crushed and sieved through 2 mm mesh for the determination of the physical and chemical properties of the soil. Total nitrogen (N) was determined by Kjeldhal method after digestion of material (A.O.A.C. 1999). Available P was determined using Bray 1 method (Murphy and Rikey 1962). Exchangeable bases were done by extraction with 1 m NH 4 OAC. Calcium (Ca) and magnesium (Mg) in the extract were determined by atomic absorption spectrophotometer (AAS). Effective CEC was the summation of exchangeable bases (Ca, Mg, K, and Na); potassium (K) was determined by flame photometer, and pH (H 2 O) using a pH meter. Percentage organic carbon was estimated by chromic acid digestion. Data were subjected to analysis of variance and the mean data were compared using the least significant difference (LSD) at p [ 0.05.

Pre-field soil analysis
The results of the physical and chemical analysis of the potted soil before cropping are presented in Table 1. The soil was mostly sandy loam in texture with pH of 7.7. Total N content was 0.9 mg g -1 , available P was 1.95 mg g -1 , K 0.21 c mol kg -1 , Fe 6.15 mg g -1 , Zn 1.18 mg g -1 and Mn value was 45.45 mg kg -1 ( Table 1).

Analysis of organic material
The nutrient content of poultry manure, cow dung and organomineral used in the experiment is represented in Table 2. It indicated that there were differences in nutrient composition of organic components. N, P and K contents of poultry manure were higher in value than cow dung and organomineral.
Effects of soil amendments on vegetative growth of M. oleifera

Plant height
There were significant (p [ 0.05) differences in the plant height between those treated with fertilizers and the control. Results indicated that at all growth stages, plant height observed for all the fertilizer types and rates were all higher than the control, where the average values for control were 13.0, 26.1, 47.5 and 74.7 cm for 5, 7, 9 and 11WAS; plant height for 20 tons ha -1 of poultry manure (PM) was 27.2, 61.3, 111.6 and 157.4 cm, respectively. At 11WAS, 30 tons ha -1 PM had the highest plant height. This performance was followed in ranking by 20 tons ha -1 PM (157.4 cm) and 10 tons ha -1 PM (Table 3).

Stem girth
Stem girth values obtained for all organic and NPK rates were higher than the control at all stages of data measurements, where the values obtained for control were 0.3, 0.5, 0.9 and 1.4 cm; the highest values of 0.8, 2.0, 2.2 and 2.5 cm were obtained from 20 tons ha -1 PM. At 11WAS, 30 tons ha -1 PM application resulted in the highest value of stem girth obtained in the experiment. Poultry manure at all levels of application in the study resulted in stronger stem. Performance of PM was followed by application of 20 and 30 tons ha -1 cow dung (Table 3).

Number of leaves
The number of leaves produced by M. oleifera was highly influenced by application of fertilizers (Table 3). Pots without any fertilizer application had the least number of leaves at 5,7,9 and 11WAS (8.1,9.3,12.8 and 17.8), respectively, while pots with 20 tons ha -1 of PM had the highest number of leaves at 5WAS but pots with 30 tons ha -1 application had the highest number of leaves from 7WAS (15.6, 24.8, 32.3). Generally, PM at all rates produced higher number of leaves than all rates of OM, CD and NPK. The performance of seedlings with 30 tons ha -1 PM application was followed by 20 tons ha -1 OM and 30 tons ha -1 of CD in descending order. The higher the rate of poultry manure, the higher the number of M. oleifera leaves produced.

Effects of different sources and rates of nutrients on post-field soil properties
Soil nitrogen (N), phosphorus (P) and potassium (K) were significantly influenced by different rates and sources of fertilizers. For post-planting soil N and P, addition of both organic and NPK fertilizers resulted in the higher N and P soil contents than the control plots except for K (Fig. 1). Organomineral (OM) applied at 10 tons ha -1 had higher residual soil N content; this was followed by poultry manure applied at 30 tons ha -1. For K and P, it was also OM applied at 30 tons ha -1 ; this performance was followed by poultry manure. Other soil properties were determined which were significantly influenced by different rates and sources of fertilizers include: Ca, Na, Mn, Fe and Zn. Application of 30 kg ha -1 of NPK resulted in the higher residual soil content of Ca; this was followed by 30 tons ha -1 application of OM. 20 tons ha -1 application of CD on M. oleifera resulted in the higher residual content of Mg and Mn in the soil, while for Fe, it was 10 tons ha -1 application of CD; this was followed by PM applied at 30 and 20 tons ha -1 application, respectively (Fig. 2).

Discussion
The pre-planting major nutrient content of the soil was inadequate, where the minimum critical level required for crop growth in the area is 0.6-1.0 mg kg -1 for N, 3-7 mg kg -1 for P, and 0.21-0.3 cmol kg -1 for K (Adeoye and Agboola 1985). This nutrient status of the soil agreed with the results of Aduayi et al. (2002) who reported that most Nigerian soils are deficient in major nutrient, thus emphasis the need for use of sustainable soil amendments. Also nutrient analysis of organic manure (Table 2) indicated that poultry manure is higher in content in major nutrients required for optimum plant growth, such as N, P and K. This may have been responsible for significance performance by Moringa plants treated with higher rates of poultry manure. Addition of fertilizers either organic or inorganic improves Moringa growth and productivity of soils, but their performance depends on the crop type, the environment, season, variety, fertilization, and irrigation   regime. Moringa yields best under warm, dry conditions, with some supplemental fertilizer and irrigation (Radovich and Paul 2008). In this experiment, poultry manure applied at 20 tons ha -1 treated seedlings showed a significant  treated with 20 tons ha -1 of cow dung, goat droppings and poultry manure, respectively; application of poultry manure (PM) resulted in the higher growth parameters and fruit yield of tomato plants. The increasing effects of PM on moringa development and soil properties in this study also corroborated the observation of Gupta et al. (1997), Adeniyan and Ojeniyi (2005), Akanbi et al. (2005), Adenawoola and Adejoro (2005) and Agyenim-Boateng et al. (2006) that poultry manure is very rich animal manure that releases considerable soil organic matter, available P and exchangeable cations when applied to soil. Poultry manure contains all the essential plant nutrients that are used by plants; these include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), manganese (Mn), copper (Cu), zinc (Zn), chlorine (Cl), boron (B), iron (Fe) and molybdenum (Mo) (Amanullah et al. 2010). It increases the moisture holding capacity of the soil and improves lateral water movement, thus improving irrigation efficiency and decreasing the general doughtiness of sandy soils. Poultry manure application improves soil retention and uptake of plant nutrients (Amanullah et al. 2010). It increases the number and diversity of soil microorganisms, particularly in sandy conditions. This effect enhances crop health by increasing water and nutrient availability, as well as suppressing harmful levels of plant parasitic nematodes, fungi and bacteria. The cumulative effect supports the observation that poultry manure added organic matter and nutrients to the soil. This may probably be due to the fact that poultry manure contains concentrated nutrients and hence led to enhanced plant growth in those seedlings treated with poultry manure. The nutrient quality in poultry manure might surpass the ones in cow dung manure leading to more enhanced plant growth in those treated with poultry manure. This observation was between week 5 and 7 after planting. This generally implies that the plant is a fast growing species and this conforms to the earlier findings by Odee (1998) and Imoro et al. (2012) that Moringa is a fast growing plant and grows between 6 to 7 m per annum even in areas receiving less than 400 mm of rainfall. The significance influence of organomineral (OM) on residual soil content of N, P and K may also be because, OM was fortified with mineral N, P and K. The bulk of cow dung manure might probably be materials that do not significantly enhance plant growth as compared to those found in poultry manure. Other authors found significant improved height in M. oleifera using poultry manure (Agyenim-Boateng et al. 2006;Imoro et al. 2012). The organic matter component of poultry manure were higher, and when decomposed in soil, nutrients were released to soil. Hence the findings that poultry manure increased soil N, P, K, Ca, and Mg significantly.

Conclusion
Application of poultry manure, cow dung manure, organomineral and NPK had significant effects on the growth of M. oleifera over controls. However, poultry manure treatments had the best growth attributes for optimal yield. Therefore, the treatment with 20 tons ha -1 is recommended for sustainable leaf dry matter production of M. oleifera in South-West, Nigeria.