Dynamics of soil nitrogen availability indices in a sandy clay loam soil amended with animal manures
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Transformation of nitrogen (N) from different manure sources to available forms to promote food security in context of rising climate change is vital. Effect of manure (types, nutrients, high rates and application time) on soil N transformation requires further investigation. This study evaluated effects of three animal manures on soil N mineralization of sandy clay loam.
A 22-week field study in a Randomized Complete Block Design (three replicates) was conducted using dried Cattle, Goat and Poultry Manures (CGPM), applied at 5, 10, 20, 40, 60, 80, 120 and 150 t ha−1 once at onset of the study. Also, N15P15K15 (0.4 t ha−1) was incorporated in three splits of 2, 8 and 14 weeks after incorporation (WAI) of manures as reference. Soil NH4+–N and NO3−–N were determined bi-weekly.
The results showed N release peaked at 10 WAI with highest NH4+–N (830, 400, 253 mg kg−1) and NO3−–N (316, 398, 250 mg kg−1) at 150, 60 and 60 t ha−1 for CGPM, respectively. Initial rapid N release phase occurred at 0–4 WAI, NH4+–N and NO3−–N increased averagely by 182, 183, 139% and 131, 175, 144% for CGPM, respectively. Declines occurred at 8, 14 and 22 WAI but reduction observed at 22 WAI tripled 8 and 14 WAI.
Application of NPK and all the manures provided highest soil NH4+–N and NO3−–N at 12 WAI. High rates of CGPM were not injurious to these soil properties; hence this has implication for N to maximize plants uptake as well as decrease losses to environment.
KeywordsAnimal manures Rates NPK fertilizer and nitrogen mineralization
Agricultural growth as a result of population increase had contributed to intensification of land cultivation; this causes severe soil fertility depletion. However, losses of nutrients in the soil have been replenished through the use of animal manures (Ramsasa 2010). Hence, the potential of animal manure use in soil replenishment has received the global attention. Currently, to many soil fertility difficulties, animal manures offer an affordable and readily available solution (Spore 2006) and are important source of Ca, Mg, S and micronutrients (Gomez-Brandon et al. 2013); they contain low and highly variable amounts of N, P and K. Aside from being source of plant nutrients, the physical properties of soil are also improved (Akanni and Ojeniyi 2008). However, the use of animal manures can pose a major problem of excess nitrate in soil (Azeez and Van Averbeke 2010b; Navarro Pedreno et al. 1996). The difficulty in the prediction of manure nutrients to plants is due to turnover processes and losses in manures (Azeez and Van Averbeke 2010a; Sorenson 2001). Therefore, incorporation of animal manures to supply nitrogen in proper dose at the proper time without posing any injury to soil and plants is very important in soil replenishment to support crop productivity. Hence, in order to predict the net mineralization of nitrogen in animal manures, transformation of nitrogen from organic into inorganic form and immobilization processes need to be understood. These processes are mediated through microbial activities and naturally, they are biochemical (Vel and Swamam 2013; Bartholomow 1965). Large variability in manure qualities (Chadwick et al. 2000) or types had posed difficulties for researchers in concluding on a specific rate of manure to support development of different crops. The consequence of these led to differences in the recommendations of 60 t ha−1 of cattle kraal manure for Corchorus olitorius L. (Masarirambi et al. 2012b), goat manure rate of 20 t ha−1 for sweet maize (Uwah and Eyo 2014); and poultry manure at the levels of 60 t ha−1 (Masarirambi et al. 2012a) and 30 t ha−1 (Enujeke et al. 2013) for lettuce and maize yield, respectively.
Animal manures at proper application time, adequate rates and proper nutrient contents when expanding the uses of organic matter in place of inorganic fertilizers for nitrogen mineralization to meet crop N requirement without adverse problem on soil, crop and the environment need to be investigated. This necessitated the study to (1) examine the release patterns of NH4+–N and NO3−–N from different rates of three animal manures and recommended inorganic fertilizer rate to soil, (2) evaluate the potential rates of mineralization of the three animal manures on soil and (3) determine the influence of high application rates of the three animal manures on soil.
Materials and methods
Location of the experiment
Agrometeorological data for the period of the experiment
Agrometeorological data for the period of the experiment
Mean Temp./day (°C)
Soil Temp./day (°C) (20 cm)
Average RH/day (%)
Mean sunshine (h/day)
The experiment was a randomized complete block design (RCBD) with three replicates. Cattle, goat and poultry manures were applied at the rates of 5, 10, 20, 40, 60, 80, 120 and 150 t ha−1 separately; these were used to test the pattern of manure mineralization irrespective of the rates, to test the manure-induced soil factors that affect plant growth and also evaluate the residual effect of manure rates on soil properties. NPK 15–15–15 fertilizer was used as check for each manure treatment and applied at the rate of 400 kg ha−1 (Schippers 2000). Starting from 2 weeks after incorporation of manures but a day after application of NPK fertilizer, soil samples were collected at every 2-week intervals from the net portion of each bed at a depth of 0–15 cm with the exception of 6 and 16 WAI due to rainfall failure. The samples were air dried, prepared for laboratory analysis and analyzed for NH4+–N and NO3−–N.
Soil and manures analyses
Initial soil sample and those collected bi-weekly were analyzed using the following methods. Soil EC and pH were extracted with 1:2 soil:water ratio and measured potentiometrically using HANNA 215 electrical conductivity meter (Richards 1954) and glass pH meter electrodes (HANNA pHep), respectively, (Van Reeuwijk 1993). The NH4+–N and NO3−–N were extracted in 2 Molar K2SO4 and determined colorimetrically using the method of Okalebo et al. (1993). Available P was extracted by Bray P-1 extraction (Bray and Kurtz 1965), obtained colorimetrically (Murphy and Riley 1962). Exchangeable bases were extracted with 1 N Ammonium-acetate solution in 1:10 soil solution ratio, K+ and Na+ were analyzed with flame photometer, while Ca2+ and Mg2+ with Atomic Absorption Spectrophotometer (AAS) (Anderson and Ingram 1993). Organic carbon (OC) content was determined by Walkley–Black method (Nelson and Sommers 1990) and particle size by hydrometer method (Bouyoucos 1965).
The cattle, goat and poultry manures used were digested with nitric per chloric acid (2:1) (Watanabe et al. 2013; Silva and QueirÓz 2002). The digests were analyzed for macronutrients and micronutrients using standard procedures (Kaira and Maynard 1991; Cater 1993). Distilled water was used for extraction to determine the electrical conductivity and pH of the manures.
Data collected were subjected to Analysis of Variance (ANOVA) using SAS (1999). Duncan Multiple Range Test at 5% level of probability was used to determine differences in the treatment rates means and also to show the significance effects on parameters measured in relation to the control.
Agrometeorological data for the experimental period
Agrometeorological average data for rainfall, relative humidity, mean temperature, soil temperature, mean sunshine hour and evaporation at 2-week intervals during the experiment were presented in Table 1.
The result revealed that the soil used for the research had EC value of 0.69 dS m−1, pH of 7.6 and total N value of 0.8 g kg−1. The NH4+–N, NO3−–N, OC and available P values were 0.013, 0.014, 14.2 g kg−1 and 7.5 mg kg−1, respectively. Exchangeable bases; K+, Na+, Ca2+ and Mg2+ had the values of (0.42, 0.82, 10.96 and 1.34) cmol+ kg−1, respectively. The carbon to nitrogen ratio (C: N) was 11.83. The micro-nutrients; Mn2+, Fe2+, Cu2+ and Zn2+ had the values of (55.1, 9.85, 1.2 and 5.1) mg kg−1, respectively. The percentages of sand, silt and clay were 770, 68 and 162 g kg−1, respectively.
Equivalent amount of nutrients present in cattle manure rates added to the soil
Rates (t ha−1)
Cattle manure nutrients (kg)
Equivalent amount of nutrients present in goat manure rates added to the soil
Rates (t ha−1)
Goat manure nutrients (kg)
Equivalent amount of nutrients present in poultry manure rates added to the soil
Rates (t ha−1)
Poultry manure nutrients (kg)
Effect of cattle, goat and poultry manures on soil NH4+–N and NO3−–N (mg kg−1)
Effect of cattle manure on soil NH4+–N (mg kg−1)
Influence of cattle manure rates and NPK fertilizer (t ha−1) on mean soil NH4+–N (mg kg−1) at 2 weeks intervals
Rates (t ha−1)
Means of bi-weekly analyses of soil NH4+–N (mg kg−1) with applied cattle manure
Effect of goat manure on soil NH4+–N
Influence of goat manure rates and NPK fertilizer (t ha−1) on mean soil NH4+–N (mg kg−1) at 2 weeks intervals
Rates (t ha−1)
Means of bi-weekly analyses of soil NH4+–N (mg kg−1) with applied goat manure
Effect of poultry manure on soil NH4+–N
Influence of poultry manure rates and NPK fertilizer (t ha−1) on mean soil NH4+–N (mg kg−1) at 2 weeks intervals
Rates (t ha−1)
Means of bi-weekly analyses of soil NH4+–N (mg kg−1) with applied poultry manure
Effect of cattle manure on soil NO3−–N
Influence of cattle manure rates and NPK fertilizer (t ha−1) on mean soil NO3−–N (mg kg−1) at 2 weeks intervals
Rates (t ha−1)
Means of bi-weekly analyses of soil NO3−–N (mg kg−1) with applied cattle manure
Effect of goat manure on soil NO3−–N
Influence of goat manure rates and NPK fertilizer (t ha−1) on mean soil NO3−–N (mg kg−1) at 2 weeks intervals
Rates (t ha−1)
Means of bi-weekly analyses of soil NO3−–N (mg kg−1) with applied goat manure
Effect of poultry manure on soil NO3−–N
Influence of poultry manure rates and NPK fertilizer (t ha−1) on mean soil NO3−–N (mg kg−1) at 2 weeks intervals
Rates (t ha−1)
Mean of bi-weekly analyses of soil NO3−–N (mg kg−1) with applied poultry manure
The soil used for the research was sandy clay loam (USDA 2010), slightly saline (LAS 2014), and slightly alkaline (Pam and Brian 2007) and these could support plant performances. More so, the soil was deficient in total nitrogen (McBride 2015; USDA-SCS 1974) and had low available P content (ENDMEMO 2015; Mallarino 2000) which could retard crop development. It contained moderate OC (McBride 2015; USDA-SCS 1974), exchangeable K+ and Mg2+ (Pam and Brian 2007); these were optimal for performance of the crop. The high exchangeable Na+ and Ca2+ contents (Pam and Brian 2007) could be attributed to the decomposition of the organic matter content of the soil due to high temperature, evaporation rate, sunshine hours/day and low rainfall during the research. This confirmed the studies of some researchers (Davidson and Jannssens 2006; Friedlingstein et al. 2006). The NH4+–N and NO3−–N contents were low and C: N ratio was considered normal (Hill 2001) and could be as a result of low rainfall during this period. The copper, iron and zinc contents were very high (Enwezor et al. 1989).
The EC of the three manures applied were very strongly saline (LAS 2014). This could be as a result of high concentration of cationic salts in the manures. More so, the highest EC value of poultry manure compared with the cattle and goat manures support the findings of Azeez and Van Averbeke (2010a, b) and could be attributed to the highest NH4+–N, NO3−–N and total P contents in poultry manure compared to others. The pH of the pure goat and poultry manures was considered mildy alkaline, whereas that of cattle manure was moderately alkaline (Pam and Brian 2007). This would allow for nutrients availability in the soil after mineralization. It was observed from the result that cattle manure had the highest total K, Na and Ca over the goat and poultry manures. However, goat manure was higher in total N, Mg and OC in relative to cattle and poultry manures. Very low value of total P in goat manure could be a result of the nutrient concentrations of the feed given to the animals. This is because they were fed with elephant grasses and wheat offal under intensive system although the nutrient contents of the feed were not measured. Equivalent amount of total N contents present in goat manure applied was higher than cattle and poultry manures. High P content in poultry manure could also contribute to the yield quality of crops at lower rates than cattle and goat manures. Cattle manure recorded highest equivalent amount of pH, total K, Na and Ca than goat and poultry manures; this could be attributed to the higher EC value in cattle manure than goat manure and confirmed the report of Monica (2013). Highest contents of total N, Mg and OC in goat manure compared with cattle and poultry manures suggested the reason for lowest value of EC in goat manure applied during the studies. This is because Mg was the only salt forming cation that was highest in goat manure. Highest total N could be a result of N level in the feed given to the goat animals, although the nutrient contents of the feed were not determined.
Manure mineralization processes in the soil
Incorporation of cattle, goat and poultry manures increased the concentration of NH4+–N; this supports the findings of Sajal and Abul Kashem (2014) and NO3−–N depending on the rates (Eghball et al. 2002) compared with control. However, the low values of NH4+–N between 0 and 8 WAI of the manures could be attributed to conversion of NH4+–N to NO3−–N as supported in the study of (Hoskins 2015) that, between 2 and 4 weeks, NH4+–N converted relatively quickly to NO3−–N in a soil applied with broiler manure. However, mineralization of organic N into inorganic form of NH4+–N and NO3−–N occurred between 8 and 14 WAI of manures. Consequently, the low NH4+–N between 18 and 22 WAI could be attributed to ammonia volatilization (Meissinger and Jokela 2000) while low NO3−–N contents between 18 and 22 WAI could be attributed to leaching (Tom 2002; Marco et al. 2002) and plant root uptake. The low NO3−–N contents in soil applied with NPK fertilizer at 18 WAI compared with 8 and 14 WAI could be attributed to acidic properties of NPK fertilizer, since acidity reduces soil microbial activity and this would in turn reduce nutrient mineralization (Xu et al. 2002).
Mineralization of NH4+–N and NO3−–N contents occurred in the soil with the maximum values at 10 WAI for cattle, goat and poultry manures but was contrary to the results of Azeez and Van Averbeke (2010b) that sharp increase in N release was at 120 days; and (Ayeni 2011; Ayeni and Adeleye 2011), that release of poultry manure nutrients proportion is between 1 and 2 months of incubation. The variability of mineralization processes could be attributed to microbial activities as suggested by Vinten et al. (2002); and climatic variations. Hence, the turnover processes and losses have influence on availability of nutrients in manures; this is why the prediction of manure nutrients to plants is problematic (Azeez and Van Averbeke 2010b; Sorenson 2001).
Very low N mineralization at 14 WAI compared to 12 WAI could be attributed to very low rainfall during this period. This corroborated the report of Jonathan (2006) that in dry soils, N mineralization is low because soil micro-organism activity is limited by water availability. More so, low NH4+–N suggested to be as a result of volatilization of NH3 as this is favored by warm temperature wet soils under drying conditions (Tom 2002; James 2001). While low NO3−–N could be as a result of leaching that might have occurred at 12 WAI due to very high rainfall at this period, this also corroborated the work of Tom (2002) that NO3 in the soil can be lost through percolation of water below the active root zone.
Across weeks after incorporation of the three manures, application rates of 20 t ha−1 for cattle, 40 t ha−1 for goat and poultry manure at the rate of 10 t ha−1 were not widely significantly different when compared to higher rates. Therefore, addition of manures more than these rates to the soil could lead to wastage as these did not increase the amount of NH4+–N and NO3−–N in the soil sequentially according to this study. Although the high rates of cattle, goat and poultry manures were significantly higher relative to lower rates in this research, these suggested not to be encouraged as the increments were not regular across the weeks after manure application. The irregularity could be attributed to volatilization (Meissinger and Jokela 2000) and leaching (Tom 2002; Marco et al. 2002) of the NH4+–N and NO3−–N in the soil, respectively.
During this work, NPK fertilizer applied was able to supply equal amount of NH4+–N to the soil when compared with 10 t ha−1 of cattle manure treatment between 2 and 12 WAI. But goat manure treated soil at 60 t ha−1 supplied equal amount of NH4+–N compared to NPK fertilizer between 2 and 8 WAI, while 40 t ha−1 of poultry manure was able to supply equal amount of NH4+–N to the soil compared to NPK fertilizer at 0.4 t ha−1 between 2 and 8 WAI. This suggested that cattle, goat and poultry manures incorporated to the soil at 10, 60 and 40 t ha−1, respectively, supplied equal amount of NH4+–N compared to NPK fertilizer at 0.4 t ha−1 within 6 weeks. The low NH4+–N and NO3−–N contents of the soils applied with NPK fertilizer at 14 WAI compared with cattle, goat and manure treated soils rates could be attributed to acidic properties of NPK fertilizer. This corroborated the study results of Xu et al. (2002) that acidity reduces soil microbial activity resulting in reduced nutrient mineralization. This could also be attributed to depletion of soil organic matter as a result of synthetic fertilization (Jonathan 2006).
Conclusion and recommendation
Generally, addition of NPK 15–15–15 fertilizer, cattle, goat and poultry manures improved the soil NH4+–N and NO3−–N compared with control. The NH4+–N and NO3−–N contents of the soil between 2 and 8 WAI increased with the application of cattle, goat and poultry manures. However, between 8 and 14 WAI mineralization of NH4+–N and NO3−–N occurred but peak values were obtained at 10 WAI irrespective of the manures types and rates. Finally, the effect of cattle, goat and poultry manures on NH4+–N and NO3−–N decreased between 18 and 22 WAI.
To increase soil NH4+–N and NO3−–N for optimum production of crops yield, application of cattle, goat and poultry manures is recommended. It is recommended that application rate of 20 t ha−1 for cattle, 40 t ha−1 for goat and poultry manure at the rate of 10 t ha−1 would provide optimum and improve the soil nutrients level which will be retained in the soil for longer period. To improve soil with low N contents, poultry manure is recommended. Meanwhile, addition of cattle, goat and poultry manures to supply NH4+–N and NO3−–N to the soil with regard to sowing dates is recommended to be 2 WAI as this would allow equilibration of the manures with the soil prior to planting, while incorporation of these three manures for crop needs is recommended to be 8 WAI.
The assistance of people that contributed to the success of this research is gratefully appreciated while the expressions, views and conclusions attained are for the authors.
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