Controlled-Release NPK Fertilizer Encapsulated by Polymeric Membranes
The commercial granular fertilizer NPK6-20-30 was coated using polysulfone (PSF), polyacrylonitrile (PAN), and cellulose acetate (CA). The coatings were formed from the polymer solutions by the phase inversion technique. Measurements of the thickness and porosity of the prepared coatings and a microphotographic observation of the coatings were performed. The physical properties of the coatings influence the release rate of macronutrients which are present in the core of the coated fertilizer. In the case of PAN coating with 60.45% porosity, prepared from a 16% polymer solution, 100% of NH4+ and P2O5 was released after 4 h of test and 99.7% of K+ after 5 h of test, whereas in the case of coating with 48.8% porosity, 31.8% of NH4+, 16.7% of P2O5, and 11.6% of K+ was released after 5 h. In all experiments, different selectivities of the coatings in terms of the release of components were observed. The release of potassium through the coatings made of PSF and PAN was the slowest. The same tendency was observed for the release of nitrogen through a coating of CA. The release of fertilizer active components was the slowest in the case of PSF. The lowest porosity coating was prepared from the 18% PSF solution. 
Use of Polysulfone in Controlled-Release NPK Fertilizer Formulations
Encapsulation of fertilizers in polymeric coatings is a method used to reduce fertilizer losses and to minimize environmental pollution. Polysulfone was used for a coating preparation for soluble NPK granular fertilizer in controlled-release fertilizer formulations. The coatings were formed by the phase inversion technique (wet method). The influence of the polymer concentration in the film-forming solution on the physical properties of the coatings was examined. The coating structure controls the diffusion of the elements from the interior of the fertilizer granule. It was experimentally confirmed that the use of polysulfone as a coating for a soluble fertilizer decreases the release rate of components. Moreover, the release rate of nutrients from coated granules decreases with the decrease of the coating porosity. In the case of coating with 38.5% porosity, prepared from 13.5% polymer solution after 5 h of test, 100% of NH4+ was released, whereas only 19.0% of NH4+ was released after 5 h for the coating with 11% porosity. In addition, coating of fertilizers leads to improvement of handling properties, and the crushing strength of all coated fertilizers was an average 40% higher than that for uncoated NPK fertilizer. 
Microbial biomass C, N and P in two arctic soils and responses to addition of NPK fertilizer and sugar: implications for plant nutrient uptake
The soil microbial carbon (C), nitrogen (N) and phosphorus (P) pools were quantified in the organic horizon of soils from an arctic/alpine low-altitude heath and a high-altitude fellfield by the fumigation-extraction method before and after factorial addition of sugar, NPK fertilizer and benomyl, a fungicide. In unamended soil, microbial C, N and P made up 3.3–3.6%, 6.1–7.3% and 34.7% of the total soil C, N and P content, respectively. The inorganic extractable N pool was below 0.1% and the inorganic extractable P content slightly less than 1% of the total soil pool sizes. Benomyl addition in spring and summer did not affect microbial C or nutrient content analysed in the autumn. Sugar amendments increased microbial C by 15 and 37% in the two soils, respectively, but did not affect the microbial nutrient content, whereas inorganic N and P either declined significantly or tended to decline. The increased microbial C indicates that the microbial biomass also increased but without a proportional enhancement of N and P uptake. NPK addition did not affect the amount of microbial C but almost doubled the microbial N pool and more than doubled the P pool. A separate study has shown that CO2 evolution increased by more than 50% after sugar amendment and by about 30% after NPK and NK additions to one of the soils. Hence, the microbial biomass did not increase in response to NPK addition, but the microbes immobilized large amounts of the added nutrients and, judging by the increased CO2 evolution, their activity increased. We conclude: (1) that microbial biomass production in these soils is stimulated by labile carbon and that the microbial activity is stimulated by both labile C and by nutrients (N); (2) that the microbial biomass is a strong sink for nutrients and that the microbial community probably can withdraw substantial amounts of nutrients from the inorganic, plant-available pool, at least periodically; (3) that temporary declines in microbial populations are likely to release a flush of inorganic nutrients to the soil, particularly P of which the microbial biomass contained more than one third of the total soil pool; and (4) that the mobilization-immobilization cycles of nutrients coupled to the population dynamics of soil organisms can be a significant regulating factor for the nutrient supply to the primary producers, which are usually strongly nutrient-limited in arctic ecosystems. 
Effect of NPK Fertilizer on Fruit Development of Pumpkin (Cucurbita pepo Linn.)
The effect of NPK fertilizer on pumpkin fruit development was studied for two cropping seasons in 2010 at the Teaching and Research Farm, Obafemi Awolowo University, Ile-Ife, Nigeria in 2010. The experiment was a randomized complete block design. The plants were treated with six NPK rates (0, 50, 100, 150, 200 and 250 kg/ha). Data on fruit weight, circumference, length and dry matter were obtained at 7, 14, 21 and 28 days after fruit formation. Increasing NPK fertilizer enhanced the parameters evaluated across the sampling periods. Fresh fruit weight (g/fruit) in control was 39g, 123g, 822g and 1059g and this increased to 80g, 370g, 1350g and 1630g at 7, 14, 21 and 28 days after fruit formation respectively at 100 kg NPK fertilizer rate. Across the NPK levels, pumpkin fruit growth curve was sigmoid. The fruit took approximately 22 days from fruit formation to fruit maturity across all the NPK fertilizer levels. In conclusion, excessive NPK supply did not significantly increase the rate of fruit growth or the fruit size. Fruit growth duration of pumpkin was not influenced by NPK fertilizer application. 
Comparative Effect of Pig Manure and NPK Fertilizer on Agronomic Performance of Tomato (Lycopersicon esculentum Mill)
Field experiments were performed to investigate the effectiveness of pig manure (PG) used alone and combined with NPK fertilizer on nutrients composition, growth and yield of tomato (Lycopersicon esculentum Mill.). Treatments were replicated three times in a randomized complete block design and applied to tomato seedlings grown on beds at Oba-Ile and Iju in the rainforest zone of Southwest Nigeria Six treatments compared were: (a) the control, (b) 25t/ha pig manure, (c) 250kg/ha NPK (15:15:15) fertilizer, (d) 187kg/ha NPK + 6t/ha PG (75:25), (e) 125kg/ha NPK + 12t/ha PG (50:50) and (f) 62kg/ha NPK + 18t/ha PG (25:75) Soil and plant nutrients composition, growth parameters and fruit weight were determined. The test soils were sandy loam, low in organic matter and marginal in Nitrogen. Pig manure, NPK, used alone or combined at reduced rates significantly increased soil N, P, K, Ca, Mg, number of leaves, plant height, stem girth and fruit weight significantly. The 187kg.ha NPK + 6t/ha PG gave highest soil N, leaf N and fruit weight. Combinations of NPK and PG gave relatively high soil N, Ca and Mg and adequate concentrations of leaf N, P, K, Ca and Mg. Mean fruit weight per plant given by the control and 187kg/ha NPK + 6t/ha were 91 and 1016 gm respectively. 
 Jarosiewicz, A. and Tomaszewska, M., 2003. Controlled-release NPK fertilizer encapsulated by polymeric membranes. Journal of Agricultural and Food Chemistry, 51(2), pp.413-417.
 Tomaszewska, M. and Jarosiewicz, A., 2002. Use of polysulfone in controlled-release NPK fertilizer formulations. Journal of agricultural and food chemistry, 50(16), pp.4634-4639.
 Jonasson, S., Michelsen, A., Schmidt, I.K., Nielsen, E.V. and Callaghan, T.V., 1996. Microbial biomass C, N and P in two arctic soils and responses to addition of NPK fertilizer and sugar: implications for plant nutrient uptake. Oecologia, 106(4), pp.507-515.
 M. Oloyede, F., O. Agbaje, G. and O. Obisesan, I. (2013) “Effect of NPK Fertilizer on Fruit Development of Pumpkin (Cucurbita pepo Linn.)”, Journal of Experimental Agriculture International, 3(2), pp. 403-411. doi: 10.9734/AJEA/2013/2102.
 Awosika, O. E., Awodun, M. A. and Ojeniyi, S. O. (2014) “Comparative Effect of Pig Manure and NPK Fertilizer on Agronomic Performance of Tomato (Lycopersicon esculentum Mill)”, Journal of Experimental Agriculture International, 4(11), pp. 1330-1338. doi: 10.9734/AJEA/2014/3959.