Introduction
Each year, the finite capacity of tropical soils grow food and fiber has progressively decreased, largely because of the decline in soil fertilityReference Parr, Papendick and Colacicco1–Reference Adeoye, Sridhar, AdeOluwa and Akinsoji4. Therefore, management of the soil in order to prevent further degradation and declining soil productivity is imperativeReference Babalola and Akoroda5.
Conventionally, farmers use mineral fertilizers that are usually not readily available in most developing countries. Currently, some commercial organic fertilizers (OFs) and organo-mineral fertilizers (OMFs) are being developed. The mineral fertilizer (mostly NKP) is currently at least four times more expensive than the most expensive organic sources. This necessitates the search for local materials that can be readily available (as fertilizers) to peasant farmers; even if they are not as effective as the conventional ones. In this case, OFs readily come to mind. One of the major problems with OF sources is their low nutrient status, a situation that could be corrected by fortification with higher nutrient sources.
Benefits of OFs include the slow-release pattern of N and S, supply of most of the essential cations and micronutrients, contribution to the soil pore system (macroporosity, microporosity, pore space and size distribution and type of soil structure), aggregate stability, soil crusting, water retention, water movement, soil strength, penetration resistance, soil compaction and bearing capacityReference Greenland and Dart6, Reference Agboola7. Application of OFs improves soil physical properties by improving porosity and aggregate stability, thereby reducing formation of a surface crustReference Greenland and Dart6, Reference Agboola7. These benefits often lead to increase productivity of crops. Thus, sustainable production of crops on tropical soils greatly requires input of OF sources.
Among organic materials of high nutrient value that can be used as alternative sources of nutrient amendment are urine, neem cake, palm kernel cake, castor oil seed cake and compost from drumstick (Moringa) tree, Gliricidia sepium and sunflower. Human urine is an excellent high nitrogenous liquid fertilizer. Studies indicate that each person's waste fluid can provide enough nitrogen, phosphorus and potassium to grow a year supply of wheat and maize for that personReference Williams8. Neem cake is a good OF because of its high a zadirachtin content with high NPK valueReference Salako, Anjorin, Garba and Omolohunnu9.
The nutrients in urine are in forms which are readily available to plants. The nitrogen is in the form of urea, which readily degrades to ammonium and nitrate, both of which are available to plants. The phosphorus is mainly in the form of phosphate ions, the potassium in the form of potassium ions and the sulfate in the form of sulfate ions. This means that they are all in forms that are taken up readily by plants. This makes urine a unique biologic fertilizerReference Höglund10. In many other parts of the world it is also a tradition to keep the urine and feces apart. The old Japanese practice of night soil recovery from urban areas separated urine and feces, since urine was regarded as a valuable fertilizerReference Matsui11. In Yemen, the urine is drained away and evaporated on the outer surface of multi-storey buildings to obtain the feces as a dry fraction without smell for later use as fuel, a system that has been in use for hundreds of yearsReference Esrey, Gough, Rapaport, Sawyer, Simpson-Hébert, Vargas and Winblad12.
Of crucial importance also is the acceptance of urine as a fertilizer by the market. At present the EU does not include human urine on the list for approved fertilizers in organic farming, whereas the International Federation of Organic Agriculture Movements (IFOAM) allows urine (and feces) if sanitary requirements are met13. In a healthy individual, the urine is sterile in the bladder. The urine can be collected in ordinary jerry cans or, if this is more suitable, in large tanks. The fate of the enteric pathogens entering the urine tank is of vital importance for the hygiene risks related to the handling and reuse of the urine. Survival studies of bacteria in urine have been performed at 4 and 20°C. Their persistence was also investigated at different dilutions of the urine and at different pH values. Bacteria were added or originally present in the urine mixture. At different time intervals, the bacteria were enumerated and T90-values (time for 90% inactivation) for the different organisms were then estimatedReference Höglund10.
Green amaranth (Amaranthus caudatus L.), a fast growing and highly nutritious crop common in the diet of Nigerians, was used as a test crop in this experiment. However, one major constraint to growing this crop is the high cost of mostly available fertilizer sourcesReference Adeoye, Sridhar, AdeOluwa and Akinsoji4.
A. caudatus was used in the present investigation because it is a good indicator plant for N, P and K nutrientsReference Adeoye, Sridhar, AdeOluwa and Akinsoji14. Fortification of compost with 50% G. sepium as a N source has been found to encourage better productivity of A. caudatus Reference Sridhar, Adeoye and AdeOluwa15. Plant growth parameters such as height, girth, number of leaves and fresh weight are often consumers' preference, while dry weight seems to more scientific. Thus, the objective of this report was to evaluate growth responses of green amaranths to application of urine, neem cake and their various fortifications of compost from market wastes. This investigation, although preliminary, could lead to further investigations in utilizing urine and neem cake in crop production and sustainable agricultural resources management for food security.
Materials and Methods
The experimental site is situated at the experimental plot of the Department of Agronomy, University of Ibadan, located in the northern limit of the lowland rainforest zone of western Nigeria (latitude 7.43°N and 3.9°E) having an annual rainfall of 1289.2 mm with bimodal distribution. Experimental soil was low in N, P and K. The choice of this soil with marginal plant essential nutrient was to ensure a response to applied treatments. The amaranth seeds and mineral fertilizer (NPK 15:15:15) were obtained from the Department of Agronomy seed store and urine used was collected from Nnamdi Azikwe Hall of the University of Ibadan and stored for a month before useReference Höglund10. Neem cake was made from crushed neem seeds obtained from Cocoa Research Institute of Nigeria (CRIN), Ibadan, Nigeria. The OF and OMF were obtained from Pacesetters' fertilizer plant, Bodija, Ibadan, Oyo State, Nigeria. The OF comprises cow dung and market waste compost in the ratio 1:3. The OMF is OF fortified (for N and P) with urea and bone meal, respectively. The investigation was a field trial laid out in a randomized complete block design with four replicates.
Table 1. Total N analysis of OFs used.
Analytical results indicated OMF having greater total N content than other treatments used, while the lowest was recorded in human urine.
The experimental soil was a loamy sand, slightly acidic with pH of 6.5 and the total nitrogen of 1 g kg−1 was lower than the critical level of 1.5 g kg−1 soil. The P content of the soil was 7 mg kg−1 which was also very low. Exchangeable Ca, K and Mg levels (0.2, 0.1 and 0.1, respectively), were also on the low side. Thus, the soil was suitable for the fertilizer trial experiment.
The investigation was carried out in two successions (main with fertilizer treatments and residual without further application) between November 2005 and February 2006. Seedbed preparation was done manually. Each experimental unit (bed) was 0.65×0.50 m in size (0.325 m2) and there were a total of 64 experimental beds, bringing the total land area for the vegetable production to 63 m2 (18×3.5 m) with 0.5 m spacing between beds. The fertilizer treatments were applied a week before planting and watered adequately to aid nutrient mineralization for plant growth. Fertilizers were applied by drilling. The amaranths plants were thinned to a planting density of 1.8 million plants hectare−1 2 weeks after planting. The experiment was carried out during the dry season, so watering to field capacity was done daily (usually in the morning). Weeding was done manually as the situation demanded.
The fertilizers were applied at a rate of 100 kg N ha−1. Treatments used were: control (no fertilizer), NPK 15:15:15, OMF (grade A), OF (grade B), urine, 90% OF+10% urine, 80% OF+20% urine, 70% OF+30% urine, 60% OF+40% urine, 50% OF+50% urine, neem cake, 90% OF+10% neem cake, 80% OF+20% neem cake, 70% OF+30% neem cake, 60% OF+40% neem cake and 50% OF+50% neem cake. Details of N content of the applied OF treatments are shown in Table 1. OMF had the highest concentration of N.
Table 2. Effects of organic nitrogen fortifiers on height (cm) of amaranth.
Means followed by the same letters in a column are not significantly different by Duncan's multiple range test at the 5% level.
1 Harvested at 4 weeks after planting.
2 Harvested at 5 weeks after planting.
Data were collected on plant height, number of leaves, stem girth, total fresh and dry weights. Soil samples were analyzed for routine physical and chemical analysis. The data on plant responses were subjected to analysis of variance and the means separated using Duncan's multiple range test.
Results and Discussion
The responses of the crops to the applied fertilizers are hereby presented.
Plant height
At the end of main planting (4 weeks after planting), the tallest plants (mean of 39.55 cm) were those treated with 40% urine N amended OF (Table 2), though not significantly (P>0.05) different from effects of other treatments apart from those of control, OMF and OF. The residual effects of the treatments (at 5 weeks after planting), however, took different dimension; the highest crops were those treated with 100% neem cake N (mean of 22.49 cm) with least resulting from those treated with mineral fertilizer NPK, urine and 20% urine fortified OF.
Number of leaves
At the end of main planting (4 weeks after planting), plants (mean of 39.55 cm) treated with 10% neem N amended OF resulted in the highest significantly (P<0.05) different mean number of leaves of 12.88, though not significantly different from effects of 40% urine N amended OF. None of the treatments resulted in a significantly different (P<0.05) number of leaves at 5 weeks after planting (Table 3).
Table 3. Effects of organic nitrogen fortifiers on number of leaves of amaranth.
Means followed by the same letters in a column are not significantly different by Duncan Multiple Range Test at the 5% level.
1 Harvested at 4 weeks after planting.
2 Harvested at 5 weeks after planting.
* Not significant (P>0.05).
Stem girth
Crops treated with 40% urine N amended OF had the highest stem girth (mean of 2.58 cm) at the end of main planting (4 weeks after planting), though not significantly different from effects of other treatments except those of control and OF. None of the treatments resulted in a significantly different (P<0.05) number of leaves (Table 4).
Table 4. Effects of organic nitrogen fortifiers on stem girth (cm) of amaranth.
Means followed by the same letters in a column are not significantly different from Duncan's multiple range test at the 5% level.
1 Harvested at 4 weeks after planting.
2 Harvested at 5 weeks after planting.
* Not significant (P>0.05).
Fresh plant weight
Crops treated with 40% urine N amended OF had the highest fresh biomass weight (mean of 269 g/plot) at the end of main planting (4 weeks after planting), which was not significantly different from effects of other treatments except those of control and OMF.
At the residual level, the 40% urine N amended OF had the highest fresh biomass weight (mean of 110.8 g plot−1) but this was not significantly different (P>0.05) from the effects of other treatments apart from NPK and 20% urine N amended (Fig. 1).
Figure 1. Effects of fertilizer treatments on total fresh weight of A. caudatus.
Dry plant weight
Crops treated with 40% urine N amended OF had the highest dry biomass weight at the end of main planting (4 weeks after planting), which was not significantly different from effects of other treatments apart from the control. During the residual effects observation, the 40% urine N amended OF had the highest dry biomass weight but was not significantly different (P>0.05) from other treatments apart from NPK (Fig. 2).
Figure 2. Effects of fertilizer treatments on total dry weight of A. caudatus.
Plant growth parameters are of interest to either the consumers or the researchers in different ways. To the consumer, his/her choice of selection of vegetable crops could be determined merely by height, stem girth or how leafy (number of leaves) such leafy vegetables. In this study, the responses of growth parameters of A. caudatus to the applied treatments vary. Depending on the interest of the consumer regarding growth parameters, choice of the best performing treatments could be made.
Most of the urine- and neem-treated plants had better growth in terms of mean height than those treated with urea-amended compost. Fertilizer NPK gave the least residual effect on plant height. This means that urine and neem used as fortifiers interacted with the OF to produce better residual effect in relation to plant height. Normally, organic manure does not release the total nutrient value in the life span of most arable crops since mineralization is slowReference Matsui11. NPK applied during the main planting might have been leached down the soil by irrigation water and the remaining exhausted by the plants. This could have been the reason why urine and neem resulted in greater value during plant growth.
Plants treated with 10% N neem, 40% N neem and 40% N urine-amended OFs producing the highest number of leaves is an indication that these treatments enhanced leaf production. The residual effects of the treatments on number of leaves was similar to that observed with respect to plant height in that 40% N urine fortification performed much like 40% N neem amendment (Table 3). The reason suggested for the result on plant height is also applicable here. Mineral fertilizer (NPK 15:15:15) produced the least number of leaves.
In the same vein, 40% N urine and 10% N neem treatments resulted in better stem girth than OMF and unamended OF (Table 4). This could have been a result of positive complementary effects of the urine and neem on the OF.
The best mean 269 g plot−1 fresh yield (34 t ha−1) of amaranths produced from 40% N urine (Fig. 1) is greater than the 20 t ha−1 obtained by AdeOluwaReference AdeOluwa16 and 30 t ha−1 reported by Grubben and Van SlottenReference Grubben and Van Slotten17. This 40% N still had the highest residual effect on mean dry yield of amaranth (Fig. 2).
The results of this preliminary experiment reveal that 40% nitrogen urine amendment of the commercial compost from market wastes (OF) seems to have greater potential to enhance plant production than Pacesetter's OF grade A (fortified with urea) (OMF) and mineral fertilizer (NPK) in terms of total fresh weight (the marketable weight). This result is in consonance with the reports of Grubben and Van SlottenReference Grubben and Van Slotten17, CookeReference Cooke18 and Perverly and GatesReference Perverly and Gates19, which stated that sole OFs perform better on some crops than mineral fertilizers.
Conclusion
From the results, it can be recommended that 40% N urine be used to compost with OF. Similarly, the neem amendment showed a tendency to perform better than urea and NPK. Depending on the parameter of interest (whether from the perspective of consumers or the scientist) the use of both urine and neem cake in agriculture is a way of putting organic wastes into productive use. This could lead to sustainable utilization of environmental resources. However, other useful impacts of the OF sources on soil health and crop quality would have to be investigated.
