High C / N Materials Mixed with Cattle Manure as Organic Amendments to Improve Soil Productivity and Nutrient Availability

Identification of organic materials, which can enrich the soil organic matter pool and improve the productivity of marginal lands, is a necessity in tropical countries. A study was conducted to comprehend the effect of organic materials of different quality on the soil carbon (C) pool size and N, P, K release from soil. Organic amendments (OA) with different complexities namely, cattle manure (CM), cattle manure-rice straw (CR), cattle manure-wood shavings (CW), and cattle manure-rice straw-wood shavings (CRW) mixtures as fresh (f) or incubated for two months (i), were used in a leaching column study, soil incubation experiment and greenhouse experiment using maize (Zea mays L.) as the test plant. The N, P and K release pattern from soil, soil organic matter content and biomass of maize in OA added soils compared to fertilizer-only (SF) and soil-only (S) treatments were determined. The nitrogen release and microbial activity were higher in fresh-OA added soils compared to other treatments. Phosphorous and K were higher in soils amended with incubated-OA than fresh-OA. The highest N, P and K release was obtained with CM-i, CRWi and CM-f, respectively. Shoot biomass of maize was enhanced by 20-40% with the application of incubated-OA compared to SF. The total soil organic C and active organic C ranged from 10.85 to 13.50 g/kg and 0.31 to 0.64 g/kg, respectively, with soils treated with OA showing significantly high values compared to the control. The organic amendments used as fresh or incubated materials, did not impede plant growth and generally maintained or improved the soil nutrient status and C pool. Incubating OA prior to application improved the nutrient availability in soil.


INTRODUCTION
Use of organic amendments is an integral part of sustainable agriculture (Ajwa & Tabatabai, 1994).Organic amendments supply nutrients and replenish the soil organic matter (OM) pool.According to several studies, organic materials improve soil chemical, physical and biological properties and thereby contribute to the maintenance of overall soil fertility and productivity (Topoliantz et al., 2005, Bhogal et al., 2011).
Application of compost, green manure and animal manure to soil is known to supply nutrients (Ohno & Crannel, 1996;Odlare et al., 2008).But the effect of organic amendments on organic matter pool is poorly studied.Repeated application of organic amendments or applications in high quantities have led to a marked improvement in soil OM pool (Miller et al., 2002;Hao & Chang, 2002).Hai et al. (2010) reported concentration of various soil organic carbon fractions increased significantly due to application of farmyard manure for a period of 26 years.Increasing soil OM pool size by applying organic amendments such as compost and manure is challenging especially in tropical environments due to high decomposition rates.
Numerous studies have been conducted regarding the effect of diverse organic material, both animal and plant based, on soil nutrients and soil chemical properties (Bulluck et al., 2002;Qian & Schoenau, 2002;Miller et al., 2012).Application of poultry manure was reported to increase soil organic matter, N and P (Agbede et al., 2008).Karami et al. (2012) reported that organic carbon, P, K, Mn and Fe increased while soil pH decreased when soil was amended with organic materials such as manure, rice husk, wheat straw, chopped reeds and licorice dregs.Short-term N availability decreased when the C/N ratio of manure exceeded 15 (Qian & Schoenau, 2002).Wheat straw rapidly decreased soil nitrate content within the first week of addition (Shindo & Nishio, 2005).Organic materials containing 0.22% or less P increased the amount of P adsorbed by soil (Singh & Jones, 1976).From 224 days long incubation study using different animal wastes, Morvan et al. (2006) found C/N ratio of the amendment significantly correlated with N mineralization rate and carbon mineralization varied from 5 to 62% of the organic C added.Thus, addition of organic inputs, especially high C/N materials to soil could cause nutrient imbalances in the short-run even though such material are required to improve soil OM content.Therefore, it is a challenge to combine different types of organic materials of diverse quality with mineral fertilizers to meet crop demands and retain or rebuild soil fertility.
Tropical climate in Sri Lanka is in favour of highly weathered and low organic matter containing soils (Mapa, 1999).One of the major limitations to crop production in Sri Lanka is low plant nutrient content (Kumaragamage, 2010).Through short-term effects on nutrient supply and long-term contribution to soil organic matter, organic materials have a prominent place in soil fertility management in the tropics (Palm et al., 2001).Thus, introducing costeffective organic materials, which could improve soil OM while complementing existing nutrient management practices, would be a best management practice.This should enable soil to strike a balance between supplying plant nutrients in the short-run and enriching nutrient reserve in the long-run.Information is scarce for tropical countries like Sri Lanka regarding the impact of organic materials of different quality on soil fertility.Therefore, this study was conducted with the aim of understanding the effect of organic materials of different quality on soil carbon pool size and the release of N, P and K using laboratory and greenhouse scale experiments.

Study site and soil sampling
Soil samples were collected from a fallowed field (110 m 2 ) in the Agriculture Training Centre, Wagolla situated in the Low-country Wet Zone (LCWZ) of Sri Lanka.The soil order is Ultisols.The land was fallowed for the past six years and was covered with grasses (dominated by Imperata cylindrica) at the time of sampling.The field was divided in to 18 grids and four random samples were collected from each grid to prepare a representative composite sample.Stones and organic debris were removed.Soil was air-dried and sieved through a 2 mm sieve prior to use in experiments.All the experiments were conducted at the Department of Soil Science, Faculty of Agriculture, University of Peradeniya.

Soil characterization
Soil pH was measured in soil: water suspension (1:2.5) using a glass electrode (McClean, 1982) and soil electrical conductivity (EC), using a conductivity meter in a soil: water suspension (1:5).Organic matter content was analysed by modified Walkley and Black method using acid dichromate (Nelson & Sommers, 1996).Cation Exchange Capacity (CEC) was measured according to Summer and Miller (1996) using ammonium acetate buffer solution.Soil texture was determined by the pipette method (Gee & Bauder, 2002).All analyses were performed in triplicates.

Preparation of organic amendments
Cattle manure was collected from the cattle shed maintained by the Faculty of Veterinary Medicine and Animal Science, University of Peradeniya.Rice straw was collected from a conventionally cultivated rice field at Thihariya and wood shavings (a mixture from Alstonia macrophylla, Swietenia macrophylla, Tectona grandis trees) were collected from a timber mill at Peradeniya.Different combinations of these organic materials were used to develop treatments.Cattle manure (CM), cattle manure-rice straw at 2:1 ratio (CR), cattle manurewood shavings at 2:1 ratio (CW), and cattle manure-rice straw-wood shavings at 4:1:1 ratio (CRW) mixtures as fresh (f) or incubated (i) were the eight treatments.Incubation was carried out at room temperature under aerobic condition for two months to facilitate partial decomposition of the material through the activity of mesophilic microorganisms.
Total organic carbon was measured by Walkley and Black method using acid dichromate and total nitrogen was determined using acid digestion followed by Kjeldhal distillation method (Bremner & Mulvaney, 1982).C/N ratio of materials was calculated.

Leaching column study
To study the effect of organic amendment on nutrient release pattern from soil, leaching columns were set-up in triplicates arranged in a complete randomized design.Each column was filled with 50g of soil after mixing with mineral fertilizer (recommended rate by the Department of Agriculture, Sri Lanka for irrigated maize crop) and organic material (fresh or incubated CM, CR, CW, or CRW at the rate of 1% w/w dry weight basis of soil).Two additional treatments of soil mixed with mineral fertilizer alone (SF) and unamended soilonly (S) were also included in the leaching column study.Leaching columns were maintained at room temperature in dark condition.Soils were leached with 100 ml distilled water at the first, second and eighth week after initiating soil incubation.Leachates were analysed for NO 3 --N, P and K. Nitrate nitrogen concentration was measured colourimetrically (Cataldo et al., 1975).Phosphorous concentration was measured using molybdenum blue colour method (Olsen & Sommers, 1982) and K using Flame Emission Spectrophotometer.

Soil incubation study
In a separate experiment, soil was mixed with each organic material in the fresh form at the rate of 1% on dry weight basis.A control was also set up using unamended soil (S).One kilogram of each treated soil was filled into plastic trays (3 cm depth) in four replicates and, covered with dark polythene and maintained in a dark room at room temperature.Moisture was maintained at 16% (gravimetric basis) throughout the incubation period using distilled water.Samples were collected after three months and analysed for total organic carbon (TOC) by modified Walkley and Black method (Nelson & Sommers, 1996) and active carbon by KMnO 4 oxidizable carbon method (Weil et al., 2003).A separate soil incubation study was maintained with fresh and incubated organic amendments (1% on dry weight basis of soil) to assess soil respiration during the first week of incubation using static incubation titrimetric method (Zibilske, 1994).

Greenhouse study
A greenhouse experiment was conducted using maize (Hybrid variety -Sampath) to study the effect of organic amendment on crop growth.Plastic pots were filled with 200g of soil mixed with mineral fertilizer at the rate developed for the experimental soil (Vinodhini, 2012) and organic material at the rates of 1% on dry weight basis.Two additional treatments as soil mixed with mineral fertilizer alone (SF) and unamended soil-only (S) were also included.The experiment was arranged in a complete randomized design with three replicates.Pots were seeded with four seeds and thinned out leaving two plants after one week.Plants were harvested after one month, oven dried at 60 o C and the shoot dry weight was measured.

Statistical analysis
Data were statistically analysed using the programme SAS 9.1.3for Windows.Time series data were analysed using mixed procedure in SAS.Duncan Multiple Range Test (DMRT) was performed to compare means for treatment effects.

RESULTS
The C/N ratio of rice straw is reported to vary from 39 to 78 when analysed using Dumas combustion procedure (Devevre & Horwarth, 2000).When cattle manure was mixed with rice straw the initial mean C/N decreased from 25 to 9 after 98 days and when the same cattle manure was mixed with a mixture of saw dust and wood shavings the mean C/N decreased from 33 to 13 after 112 days (Changa et al., 2003).In their study total C was analysed by colourimetry and total N was determined using Dumas combustion method.In the present study, incubating rice straw and/or wood shavings with cattle manure reduced the C/N of the organic material prepared (Table 1).

Release of N, P and K from Soil as affected by Organic Amendments
Soil used in the present study was sandy clay loam in texture with an OM content of 2.1%.Soil was slightly acidic (pH of 5.1) having CEC of 10.5 cmol(+)/kg and EC of 164.2 µS/cm.
The cumulative release of N, P, and K from 50 g of soil varied among treatments with values ranging from 5.7 to 19.7 mg, 0.006 to 0.01 mg and 0.4 to 3.7 mg, respectively.A definite decline in the release of all three nutrients with time was observed in the unamended soil and P release reduced with time for all treatments except for CW (f) and SF (Table 2).
In all the treatments, cumulative N release was higher compared to the unamended treatment (S).Cumulative N release relative to SF treatment was generally higher in the treatments added with fresh material (Fig. 1).Significantly high N release was observed from soils amended with cattle manure (CM) both as fresh and incubated material in the first week.
When cumulative N release for the whole period was considered, incubated CM showed a higher release than fresh CM.Higher amount of N was released from CM (i) and CR (i) than their fresh counterparts.CRW (i) showed the lowest N release followed by CW (i).
Cumulative P release from soil was noticeably higher when incubated material was added than SF and S treatments (Fig. 1)  All the treatments with amendments showed higher cumulative release of K compared to the S treatment.Organic amendments with fertilizers in combination caused higher K release than fertilizer alone (SF) treatment (Fig. 1).Fresh cattle manure (CM (f)) released the highest amount of K over time (Table 2).In general, incubated materials released higher amount of K than the fresh materials.

Soil carbon
After three months of incubation, total organic carbon and active carbon (labile fraction) contents in soil were significantly improved by the addition of organic amendment (Table 3).

Soil respiration
Application of organic materials resulted in higher respiration than soil only (S) treatment (Fig. 2).Microbial activity as indicated by respiration was significantly higher (P<0.05)when the added material was fresh compared to those of incubated.

Aboveground plant biomass
Shoot dry weight of one month old maize plants that were grown with incubated organic amendments was higher relative to plants grown in SF treatment except CW (i) (Fig. 3).

DISCUSSION
The dynamics of various nutrients in the soil and the soil microbial activity are variably affected by the composition of different organic amendments applied to the soil (Kwabiah et al., 2003).Kaur et al. (2005) found that the microbial biomass was metabolically active and total N, P and K improved in soils mixed with organic amendments with or without fertilizer.
The changes in nutrient release patterns during the first few weeks after applying organic amendments are important since it has implications on crop growth.The nutrient releasing pattern from amended soils in the present study was differently affected by the type of amendment added.Furthermore, the pattern was different between nutrients.Form of organic materials, fresh or incubated, significantly affected nutrient release pattern and microbial activity in accordance with previous observations (Kwabiah et al., 2003;Kaur et al., 2005).
Heaping of manure enhanced the availability of N (Rupende et al., 1998).Kirchmann (1991) reported that the CO 2 -C evolution rates were higher from fresh manures than from aerobically treated manures.Soil solution acquires N via mineralization, and additions through urea and cattle manure; whereas, N immobilization removes N from the available pool.Net effect of these processes resulted in N levels higher than fertilizer only (SF) treatment.As observed by Paul and Beauchamp (1994) although net immobilization of inorganic N occurred with all manures, after three weeks, net mineralization occurred from soil amended with solid and composted beef cattle manure releasing previously immobilized N. Thus, higher N release from CM (i) compared to CM (f) may be due to re-mineralization of N due to microbial activity.Cattle manure, especially CM (i), is a potential N source for fulfilling crop N requirement.Qian & Schoenau (2002) found a significant negative correlation between organic C/N ratio of cattle manure and N mineralization.Manures tended to decrease N availability in the short-term if the organic C/N ratio was over 15.Wood shaving is a high C/N ratio material compared to rice-straw.When manure was mixed with wood shavings, the NO 3 --N and total N of the soil were significantly lower than the manure only treatment (Sommerfeldt & Mckay, 1987).In the same study it was indicated that even when N fertilizer was added to manure containing wood shavings N is immobilized and N release is impeded.According to Miller et al. (2012) mineralizable soil N was reduced in aggregate sizes ≥0.47 mm when soil was amended with feedlot manure containing wood-chip compared to soils that received straw bedding.In addition to the N content, the quality and or complexity of C in the organic material also affected the nutrient release pattern as indicated by different N release pattern from materials with approximate C/N values.
Depending on the complexity, its P concentration and amount added, organic materials can either increase or decrease the P adsorption of a soil (Singh & Jones, 1976).Release of carbon accompanied P sorption indicates that soluble carbon may influence P sorption (Erich et al., 2002).Dissolved organic carbon (DOC) from decomposed organic materials enhanced extent of P release compared to DOC from fresh material (Hunt et al., 2007).Kwabiah et al. (2003) observed that some plant materials showed net P assimilation.In the present study, treating soils with incubated organic materials resulted in more P availability than amending with fresh materials.When wood shaving was added to the cattle manure-rice straw mixture the release of P was enhanced.According to Gagnon & Simard (1999) the use of wood bedding in dairy manure compost reduced P immobilization during incubation.Phosphorus sorption in soil aggregates (≥0.47 mm) in soils amended with wood-chips was lower compared to soils treated with straw bedding (Miller et al., 2012).CRW (i) has a possibility of enhancing P availability for crop growth.
In a study conducted by Tian et al. (1992) on nutrient release of a variety of plant residues, observed that all the residues released K rapidly whereas, other nutrients were immobilized to different extents.According to previous studies (Lupwayi & Haque, 1999;Eghball et al., 2002) mineralization lead to K release in large quantities from cattle manure and it may serve as a significant source of K for crop growth.Incubation process might have facilitated the mineralization of K.
Several reports indicated that the addition of organic inputs to soil increase soil organic C in addition to supplying nutrients such as N, P, and K (Rajinder et al., 2005;Butler & Muir 2006;Karami et al., 2012).Active C pool influences the nutrient cycles and soil biological properties and can act as early indicators of soil quality following soil management practices (Weil et al., 2003).Difference in active C was observed when there was a difference in soil management practices (Purakayastha et al., 2008;Culman et al., 2012).The effect of organic amendment on soil carbon content was assessed only after three months in the present study since it is equivalent to the length of a cropping season.However, it is important to assess the effects on soil carbon pool under long-term field experiments because organic matter dynamics in the presence of plants under field conditions would be different from those under laboratory incubations.Improved active C and total organic C in organic matter amended soils indicate the potentials of the tested materials to increase soil C reserves.Accordingly, CRW has the highest potential to increase soil carbon reserves among the tested materials.
Improved shoot biomass under organic amendments combined with mineral fertilizers could be attributed to the additional provision of nutrients and/ or slow release of nutrients by the organic materials improving the nutrient availability in soil over a longer period.Rice straw and wood shavings like high C/N materials mixed with cattle manure did not impede crop growth in the present study and these materials contributed to improve soil C contents.Cattle manure mixed with rice straw and/or wood shavings is better than using cattle manure or high C/N materials alone to improve soil fertility.

CONCLUSION
The composition and complexity of organic materials affect the nutrient release pattern from soil.The use of high C/N organic materials (wood shavings and rice straw) mixed with cattle manure, as freshly prepared or incubated materials did not impede plant growth and generally maintained or improved soil nutrient status and improved soil carbon levels.Incubation of wood shavings and/or rice straw with cattle manure prior to application to soil enhanced soil productivity in the short-run.Considering the positive effect on plant growth, soil nutrient status and improvements to the soil C pool, the high C/N organic materials mixed with cattle manure as used in the present study appeared to be more promising in improving soil fertility status than others.

Fig. 1 .
Fig. 1.Cumulative release of N, P, K over eight weeks from soil mixed with mineral fertilizer and different fresh (f) or incubated (i) organic materials relative to mineral fertilizer only treatment.CM-Cattle manure, CR-Cattle manure+Rice straw, CW-Cattle manure+Wood shaving, CRW-Cattle-manure+Rice straw+Wood shaving, SF-Soil+Fertilizer, S-Soil only.*Significant difference (P<0.05) between Fresh and Incubated materials.

Fig. 2 .
Fig. 2. CO 2 -C evolved from soil incubated with organic amendments in the first week after incubation.CM-Cattle manure, CR-Cattle manure+Rice straw, CW-Cattle manure+Wood shaving, CRW-Cattle-manure+Rice straw+Wood shaving, S-Soil only.Similar letters above vertical bars for each category (fresh, incubated) show means are not significantly different (P<0.05,n = 3).

Table 2
. N, P, K content in the leachate of soil mixed with mineral fertilizer and different fresh (f) or incubated (i) organic materials with time.#analysis in SAS.Means with similar letters in a given column for each category (f and i) are not significantly different (P<0.05,n = 3).

Table 3 . Total organic C and active C in soil incubated for 3 months with different organic materials
*CM-Cattle manure, CR-Cattle manure+Rice straw, CW-Cattle manure+Wood shaving, CRW-Cattle-manure+Rice straw+Wood shaving, S-Soil only).Means followed by similar letters in a given column are not significantly different (P<0.05,n = 4).