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Environmental Sustainability

, Volume 1, Issue 4, pp 437–447 | Cite as

Organic and chemical fertilizer input management on maize and soil productivity in two agro-ecological zones of Ghana

  • Richard Ansong Omari
  • Yoshiharu Fujii
  • Elsie Sarkodee-Addo
  • Yosei Oikawa
  • Siaw Onwona-Agyeman
  • Sonoko Dorothea Bellingrath-KimuraEmail author
Original Article
  • 210 Downloads

Abstract

In a two-season study, six treatments comprising three organic resources (ORs) [Centrosema pubsecens (CENT), Crotalaria juncea (CROT), and Zea mays (MZE)], two conventional chemical fertilizer (CF) applications plus control were tested at Nyankpala (Guinea savannah) and Kade (Deciduous forest) to identify suitable conditions to optimize their effects on maize yield and soil chemical and microbial biomass. Aboveground biomasses of each OR were applied to respective plots at 4 Mg ha−1 season−1, followed by basal NPK 15:15:15 and subsequent topdressing with [(NH4)2SO4] at 40 kg ha−1 and 30 kg N ha−1, respectively. Maize yield response was significant in Nyankpala compared to Kade. Average maize grain yield increased from 1.2 to 1.7 t ha−1 at Nyankpala versus 1.1 to 1.4 t ha−1 at Kade. Additionally, MZE plus CF consistently showed high average grain yield at both sites. On average, agronomic N use efficiency (AEN) increased from 4.9 to 18.3 kg grain kg−1 N applied at Nyankpala against a reduction from 13.0 to 12.3 kg grain kg−1 N applied at Kade. Moreover, AEN increased with year of cultivation in the sole CF and MZE plus CF treatments. However, CROT plus CF treatment enhanced microbial biomass compared to sole CFs at both sites. Overall, while the effects of MZE with CF application on maize yield appeared suitable at both sites, inconsistent responses were observed in CENT and CROT amendments. We conclude that soil fertility and climate are essential variables in regulating the effects of OR and CF inputs on yield and AEN in maize production systems.

Keywords

Agro-ecological zone Carbon Kade Microbial biomass Nitrogen Nyankpala Organic resource 

Introduction

Low soil fertility which characterizes many tropical small-holder agro-ecosystems remains a significant impediment to the recurring low crop yield output in developing countries. Such low soil fertility thresholds in some areas have mainly arisen as a result of soil nutrient depletion from continuous cultivation amidst poor fertilization practices (Sanchez 2002). In many developed countries, adequate fertilizer is applied (Bakht et al. 2009), in contrast to low application rates in developing economies. With the global price instability of chemical fertilizers (CFs), available organic resources (OR) in combination with inorganic sources present sustainable options to supplement the nutrient deficits in many farmlands of Sub Saharan Africa (SSA) (Chivenge et al. 2009). Meanwhile, the availability of some ORs as fertilizer remains a challenge in SSA, apart from its inherent low nutrient concentrations (Vanlauwe et al. 2005). Similarly, although there is widespread use of CFs among farmers in Ghana, optimum application rates for crop growth is seldom practiced, mainly as a result of socioeconomic constraints (Partey et al. 2013; Omari et al. 2018).

Mineralization potentials of some common tropical ORs have been evaluated (Constantinides and Fownes 1994; Handayanto et al. 1997; Omari et al. 2016), with emphasis on the synchrony between nutrient supply and crop needs. For example, the decision support system by Palm et al. (2001) suggests that low-quality ORs must be applied together with readily available nitrogen (N) sources for optimal benefits. While the effects of N additions on crop yield have widely been elucidated, few reports exist in Ghana on the soil organic carbon (C) and microbial dynamics as affected by the interaction of ORs with CFs.

The decomposition, mineralization rates and subsequent nutrient release from ORs are hugely regulated by their inherent biochemical qualities, i.e., total N, C-to-N ratio (CN ratio), cellulose, lignin, polyphenols (Palm et al. 2001; Abera et al. 2012; Rasche and Cadisch 2013). Moreover, it was earlier postulated that OR decomposition is influenced by climatic variables (Brady and Weil 1999). Hence, in different agro-ecological zones of Ghana, characterized by variable climatic factors, amendment of similar biochemical ORs will result in varying organic C amounts with distinct effects on soil microbial biomass.

Recently, soil organic C and its fractions have received considerable attention for both cropping and non-cropping reasons. While the cropping reasons relate to nutrient supply to crops, the non-cropping aspect involves greenhouse gas mitigation strategies (Thomsen et al. 2008). Organic C and its fractions in the soil are well recognized to influence soil microbial compositional dynamics (Gong et al. 2009). As such, knowledge on which OR with CF will improve soil C stocks while positively enhancing soil microbial density is essential in the tropics where soil organic matter (SOM) decomposition is high and microbial dynamics play a vital role in N cycling (Kamaa et al. 2011).

The main agro-ecological zones of Ghana are characterized by distinct climate and soil types. Such vast differences in characteristics, i.e., precipitation, temperature, soil pH, soil moisture and nutrients (Adjei-Gyapong and Asiamah 2002), influence N mineralization and crop yield. The guinea savannah (GS) zone of Ghana, characterized by an annual harmattan spells from December to March has a unimodal tropical monsoon, allowing for one growing season in a year. In contrast, the deciduous forest (DF) has bimodal equatorial rainfall pattern, which allows for two annual growing seasons. Mean temperatures in both zones do not differ significantly, unlike the relative humidity which tends to decrease from DF to GS (Barry et al. 2005). Soils in both zones, developed from highly weathered parent material are inherently infertile, or infertile as a result of human activities (Bationo et al. 2008). The soils in DF contain much more SOM and are higher in nutrients than those in GS (Bationo et al. 2008). Given these differences, optimal fertilization regime for each agro-ecological condition needs to be identified. The primary objective of this study was to evaluate the effects of contrasting ORs combined with CFs on maize yield and resultant soil microbial biomass in both zones. The specific objective was to identify suitable conditions under which the ORs could enhance maize yield and soil nutrient build up.

Materials and methods

Collection, preparation and analyses of organic materials

The aboveground biomass comprising stalk, twig, petioles, leaves, and stems of Butterfly pea (Centrosema pubsecens Benth.), Sunn hemp (Crotalaria juncea L.), and Maize stover (Zea mays L.), hereafter referred to as CENT, CROT and MZE, respectively were sampled from farmers’ fields at both study sites, oven dried at 60 °C for 72 h, ball milled to powder and analyzed in three replicates for quality parameters. The OR quality indicators [Polyphenols (PP), total carbon (TC) and total nitrogen (TN)] were determined as explained in our previous research (Omari et al. 2016). Properties of the ORs used in the study are shown in Table 1.
Table 1

Chemical quality composition of plant residue

Plant residue

TC (g kg−1)

TN (g kg−1)

CN ratio

PP (mg GAE g−1)

Centrosema pubsecens (CENT)

443.21 b

35.11 a

13

2.62 c

Crotalaria juncea (CROT)

432.35 c

24.01 b

18

3.21 b

Zea mays (MZE)

520.21 a

21.14 c

24

12.30 a

Values are the means of three replicates. Means with different letters in the same column are significantly different from each other according to LSD test at 5% probability level

TC total carbon, TN total nitrogen, CN ratio carbon-to-nitrogen ratio, PP polyphenol

Site description

Two-season field experiments were carried out in two different agro-ecological zones of Ghana; GS (Nyankpala, Savannah Agriculture Research Institute) and DF (Kade, Forest and Horticultural Crops Research Center) from 2014 to 2015. Nyankpala is in the northern region of Ghana [9°24ʹ34ʺN, 0°58ʹ46ʺW; 270 m above sea level (a.s.l.)] and has an annual unimodal rainfall amount between 800 and 1100 mm. The study site at Kade, located in the eastern region of Ghana [6°8ʹ48ʺN, 0°53ʹ58ʺW; 170 m above sea level (a.s.l.)] has an annual bimodal rainfall between 1300 and1500 mm. The mean annual temperature is 28 °C for Nyankpala and 26 °C for Kade. Figure 1 shows the mean monthly temperature and rainfall amount from 1983 to 2014 for the two study sites. The soil in Nyankpala is well-drained reddish grey savannah ochrosols, while Kade soil, characterized by relatively high SOM is defined as forest ochrosols (Adjei-Gyapong and Asiamah 2002).
Fig. 1

Mean monthly rainfall (1983–2014) and mean temperature (1983–2014) for a guinea savannah (GS) and b deciduous forest (DF) agro-ecological zones of Ghana

Soil sampling and analyses

Soil samplings were done before treatment application and immediately after harvesting. Initial composite soil samples at depth 0–15 cm were taken from five points with an auger, bulked and refrigerated at − 20 °C for the analyses of the initial basic properties. All sampled soils were first passed through a 2 mm mesh sieve and transported under the ice to Tokyo for biochemical analyses. Elemental TC and TN contents in soil were quantified by dry combustion using an automatic sensitive CN analyzer (Sumika Chemical Analysis Service Ltd., Osaka, Japan). Soil pH was determined in the supernatant suspension of a 1:2.5 soil–water mixture using Beckman PKG-260 pH meter (Beckman Coulter Instruments Inc., Fullerton, USA). Particle size distribution was determined using laser diffraction particle size analyzer (SALD-2300, Shimadzu Corporation, Kyoto, Japan) after digesting 10 g of each soil sample with 100 ml hydrogen peroxide. The SOM per unit mass of soil was determined by loss on ignition, based on the change in weight after soil samples were exposed to 550 °C (Nelson and Sommers 1996), in an Electric muffle furnace (FUL 230 FA, Advantech Toyo Co., Ltd, Tokyo Japan).

Inorganic N (NH4+-N and NO3-N) content in soil was estimated by first extracting 10 g fresh soil with 100 mL 2 M KCl. The NH4+-N and NO3-N were then determined using UV–Vis spectrophotometer (Shimadzu UV mini 1240, Shimadzu Corporation, Kyoto, Japan), following procedures as described by Parsons et al. (1984) and US EPA (1983), respectively. Soil microbial biomass was estimated using the modified fumigation-extraction method proposed by Hobbie (1998). The subsoil samples marked for fumigation were fumigated with chloroform for 72 h while non-fumigated samples were kept frozen. Afterwards, the dissolved C (TOC) (fumigated and non-fumigated) in 0.5 M K2SO4 extracts was analyzed with TOC-L (TOC-L CPH, Shimadzu Corporation, Kyoto, Japan). In the same solution, the extractable organic N was quantified as described by Ros et al. (2009) using TNM-L analyser (TOC-L CPH, Shimadzu Corporation, Kyoto, Japan). Soil microbial biomass C and N (MBC and MBN) were calculated from the difference between fumigated and non-fumigated samples. The calibration values, estimated as 0.45 for MBC (Joergensen 1996) and 0.54 for MBN (Brookes et al. 1985), were used to convert the extracted organic C and N to MBC and MBN, respectively. The surface soil (0–15 cm) of Kade and Nyankpala is shown in Table 2.
Table 2

Physicochemical properties of the experimental soils

Parameter (unit)

Site

Nyankpala

Kade

Sand (%)

79.1

42.4

Silt (%)

18.1

49.4

Clay (%)

2.8

8.2

pH (H2O)

6.2

6.0

Total C (g kg−1)

6.7 ± 0.7

13.4 ± 1.6

Total N (g kg−1)

1.3 ± 0.1

2.4 ± 0.2

CN ratio

5.2

5.6

TOC (mg kg−1)

173.4 ± 11.5

610.4 ± 21.1

EON (mg kg−1)

36.0 ± 1.0

104.3 ± 1.1

NH4+ (mg kg−1)

0.8 ± 0.4

16.4 ± 0.1

NO3 (mg kg−1)

76.7 ± 3.5

249.0 ± 51.3

Soil organic matter (%)

0.8

2.9

TOC total organic carbon, EON extractable organic nitrogen

Experimental procedure, design, and management

The soil was first cleared of weeds, debris removed, tilled to a depth of about 20 cm with a hoe, stumps removed and leveled with a rake. Similar land preparation procedure was followed at each site. The experiment was laid out in a randomized complete block design with three replications comprising six treatments including a control with no fertilization input. Each unit plot measured 4 m by 4 m. 1 m buffer plots were left between the blocks to minimize cross-border effects. At both experimental sites, the treatments comprised three biochemically contrasting ORs and two conventional chemical fertilization practices henceforth referred to as UREA and AMS. At the onset of the rains in the major growing seasons of 2014 and 2015 (8 weeks prior to sowing) at each site, the above-ground biomass of each sun-dried OR were chopped (< 10 mm) using a cutlass, broadcast at 4 Mg ha−1 and hand incorporated to a depth of 15 cm using a hoe. This is equivalent to 0.23, 0.15 and 0.14 kg N ha−1 for CENT, CROT, and MZE, respectively. At Nyankpala, ORs were incorporated on 20th February 2014 and 20th May 2015 for the first and second seasons, respectively. At Kade, ORs were incorporated on 12th March 2014 and on 27th April 2015 for the first and second seasons, respectively. Each application was followed by an initial basal N, P, and K as NPK 15:15:15 at 40 kg ha−1, 3 weeks after sowing and subsequent topdressing with [(NH4)2SO4] at 30 kg N ha−1 during tassel time. The topdressing of the two conventional chemical fertilization treatments; UREA and AMS were applied as [CO(NH2)2] and [(NH4)2SO4] at 50 kg N ha−1 season−1, respectively.

Seed maize (Zea mays), Obatanpa variety, obtained from seed stores of each research site was planted as a test crop with between row spacing of 90 cm and within row spacing of 40 cm. Sowing was done on 12th May and 18th June at Nyankpala and Kade, respectively in 2014. In 2015, sowing was done on 11th and 24th June at Kade and Nyankpala, respectively. Three seeds were planted per hill and later thinned to two after 2 weeks. Each plot at both sites was weeded with a hoe to minimize the impacts of weed pressure on the performance of maize plants. After weeding, weed litter was left on each plot as an effort to mimic the actual farmer practice. Similar agronomic practices (based on the local practices) were carried out in each site. The experiments were repeated at both sites at one-year interval during the 2014 and 2015 growing seasons. The annual rainfall at Nyankpala for the year 2014 and 2015 was 860 mm and 1000 mm with peaks occurring in September, respectively. At Kade, the annual rainfall in 2014 and 2015 were 1100 mm and 1400 mm, respectively with peaks occurring in June.

Grain yield analyses

Maize plants were harvested at physiological maturity and data on grain yields were recorded. At Nyankpala, harvesting was done in late November for both seasons while at Kade, maize plants were harvested at the end of September. In each plot, eight plants per plot were randomly selected using simple random sampling technique (Gomez and Gomez 1984). Grains were oven-dried at 60 °C for 72 h until constant weight and yield were determined at 13% moisture content.

Calculation of agronomic N use efficiency

The agronomic N use efficiency (AEN) in the ORs + N fertilizers plots was calculated as the increase in grain yield per kg of fertilizer N input (Tsujimoto et al. 2017), using the equation:
$$ {\text{AE}}_{\text{N}} = \frac{{\left( {{\text{Y}}_{\text{trt}} - {\text{Y}}_{\text{con}} } \right) \; \; ({\text{kg}}\,{\text{ha}}^{ - 1} )}}{{{\text{Total}}\,{\text{N}}\,{\text{applied}} \; \; ({\text{kg}}\,{\text{N}}\,{\text{ha}}^{ - 1} )}}, $$
where Ytrt represents yield in the OR + N fertilizer or N fertilizer treatments, Ycon represents the yield in the control treatment and total N applied represents N applied in the N fertilizer or the combined treatments.

Statistical analysis

Statistical analyses were performed with SPSS (Statistical Package for the Social Sciences, Version 16.0) software program. Site differences (Nyankpala and Kade), Year (2014 and 2015), and OR treatments (CENT, CROT, and MZE) were considered as factors. One-way ANOVA was used to compute mean differences within each factor. A three-factor general linear model was generated to detect differences in grain yield and soil properties between study sites, year of cultivation and among the OR type. Statistical significance of all effects was compared using the least significant differences (LSD) test at ρ < 0.05.

Results

Maize grain yield

The combined application of ORs with CF significantly (P < 0.05) increased the average maize grain yield over the two growing seasons at both sites (Table 3). Maize grain yield increased in 2015 at both sites for almost all treatments. Maize grain yield ranged from 0.9 to 1.6 Mg ha−1 at Nyankpala and from 0.3 to 1.8 Mg ha−1 at Kade in the 2014 growing season. In 2015, grain yield ranged from 0.5 to 2.2 Mg ha−1 at Nyankpala against 0.6 to 2.4 Mg ha−1 at Kade. Moreover, the mean maize grain yield at Nyankpala was 1.5 Mg ha−1 against 1.3 Mg ha−1 at Kade, regardless of OR amendment.
Table 3

Maize grain yield as affected by contrasting organic inputs with chemical fertilizer

Treatment

Grain yield (t ha−1)

Year 2014

Grain yield (t ha−1)

Year 2015

Average grain yield

(t ha−1)

Nyankpala

Kade

Nyankpala

Kade

Nyankpala

Kade

CON

0.9 ± 0.04 d

0.3 ± 0.02 e

0.5 ± 0.18 c

0.6 ± 0.1 d

0.7 ± 0.10 C

0.5 ± 0.06 C

UREA

1.3 ± 0.02 b

1.2 ± 0.02 c

2.1 ± 0.06 a

1.4 ± 0.2 bc

1.7 ± 0.04 A

1.3 ± 0.08 B

AMS

1.4 ± 0.10 b

0.9 ± 0.10 d

1.9 ± 0.09 a

1.7 ± 0.3 ab

1.7 ± 0.04 A

1.4 ± 0.16 AB

CENT

1.0 ± 0.10 cd

1.5 ± 0.04 b

2.2 ± 0.02 a

1.4 ± 0.3 bc

1.6 ± 0.05 A

1.4 ± 0.15 AB

CROT

1.2 ± 0.03 bc

1.8 ± 0.10 a

1.6 ± 0.06 b

1.0 ± 0.1 cd

1.4 ± 0.02 B

1.4 ± 0.06 AB

MZE

1.6 ± 0.16 a

0.9 ± 0.04 d

1.7 ± 0.10 b

2.4 ± 0.4 a

1.7 ± 0.13 A

1.7 ± 0.19 A

Means

1.2

1.1

1.7

1.4

1.5

1.3

MSD

0.19

0.13

0.30

0.70

0.15

0.38

CV (%)

5.7

4.3

5.6

18.1

3.7

10.4

R2

0.95

0.99

0.98

0.8

0.98

0.93

Different letters (a, b) within the same column indicate treatments with significant differences at P < 0.05

Treatments codes: CON, Control; UREA, CO(NH2)2; CEN, Centrosema pubescens; MZE, Zea mays; AMS, Ammonium sulphate [(NH4)2SO4]; CROT, Crotalaria juncea; MZE, Zea mays; MSD, minimum significant difference; CV, coefficient of variation

All treatments significantly (P < 0.05) increased maize yield compared to the control, except for CENT and CROT treatments at Nyankpala and Kade in the 2014 and 2015 seasons, respectively (Table 3). Maize grain yield response varied inconsistently among different fertilizer treatments and between years of cultivation. For example, in 2014, while the MZE amendment showed higher grain yield of 1.6 t ha−1 at Nyankpala, significant grain yield increase of 1.8 t ha−1 was observed in CROT treatment at Kade. Similarly, in 2015, significantly higher grain yields were recorded for CENT, UREA and AMS treatments at Nyankpala as opposed to significantly higher response in MZE-amended soil at Kade. The mean maize yield for the two seasons was in the order UREA = AMS = MZE ≥ CENT > CROT > CON at Nyankpala. In contrast, at Kade, the order was MZE ≥ CENT = CROT = AMS ≥ UREA > CON. Mean maize yield response in all amendments was twice higher than values observed in control.

Agronomic N use efficiency

The AEN differed greatly among treatments, sites and years of cultivation (Table 4). Mean AEN increased in 2015 at Nyankpala as opposed to a reduction in Kade in the same year. In 2014, AEN ranged from 1.5 to 9.8 kg grain increase kg−1 N applied at Nyankpala as against 7.5–21.6 kg grain increase kg−1 N applied at Kade. In the following year, AEN at Nyankpala ranged from 15.3 to 24.3 versus 5.2 to 25.1 kg grain increase kg−1 N applied at Kade.
Table 4

Agronomic nitrogen use efficiency (AEN) for the treatments as affected by organic inputs with chemical fertilizer

Treatment

AEN (kg grain increase kg−1 N applied)

Year 2014

AEN (kg grain increase kg−1 N applied)

Year 2015

Average AEN (kg grain increase kg−1 N applied)

Nyankpala

Kade

Nyankpala

Kade

Nyankpala

Kade

UREA

4.3 ± 0.5 bc

9.9 ± 0.4 c

18.4 ± 2.2 b

8.2 ± 3.0 b

11.4 ± 1.2 abc

9.0 ± 1.6 b

AMS

4.9 ± 0.8 b

7.5 ± 1.0 d

16.4 ± 2.9 bc

12.3 ± 4.4 b

10.6 ± 1.2 bc

9.9 ± 2.3 b

CENT

1.5 ± 0.9 c

16.6 ± 0.8 b

24.3 ± 2.7 a

10.8 ± 5.6 b

12.9 ± 1.3 ab

13.7 ± 3.0 ab

CROT

4.1 ± 0.9 bc

21.6 ± 0.6 a

15.3 ± 3.3 c

5.2 ± 2.1 b

9.7 ± 1.8 c

13.4 ± 1.3 ab

MZE

9.8 ± 1.8 a

9.7 ± 0.8 c

17.1 ± 1.4 bc

25.1 ± 6.3 a

13.4 ± 0.8 a

17.4 ± 2.8 a

Means

4.9

13.0

18.3

12.3

11.6

12.7

MSD

2.9

1.8

2.7

9.9

2.6

5.0

CV (%)

21.3

5.1

5.3

28.6

8.0

14.1

R2

0.93

0.99

0.97

0.89

0.85

0.86

Different letters (a, b) within the same column indicate treatments with significant differences at P < 0.05

Treatments codes: UREA, CO(NH2)2; CEN, Centrosema pubescens; MZE, Zea mays; AMS, ammonium sulphate [(NH4)2SO4]; CROT, Crotalaria juncea; MZE, Zea mays; AEN, agronomic N use efficiency; MSD, minimum significant difference; CV, coefficient of variation

Among the treatments, the average AEN was consistently higher in the MZE amendment at both sites (Table 4). In 2014 at Nyankpala, MZE showed the highest AEN of 9.8 kg grain increase kg−1 N applied while the lowest values of 1.5 and 4.1 kg grain yield increase kg−1 N fertilizer were observed in CENT and CROT treatments, respectively. However, at Kade in the same year, CROT and CENT showed the highest significant AEN of 21.6 and 16.6 kg increase in grain yield kg−1 N fertilizer, respectively. With respect to 2014, the AEN at Nyankpala in 2015 for CROT and CENT treatments were 3.7 and 16 times higher, respectively as opposed to 1.7 times increase in MZE treatment. However, at Kade, AEN reduced by 1.5–4.2 times in CENT and CROT treatments, respectively whereas more than twice increase was observed in MZE treatment.

Soil C and N dynamics

Amendment of ORs with CFs resulted in significant changes (P < 0.05) in soil N across sites except inorganic N and TN contents at Kade in 2014 and 2015, respectively (Table 5). Mean inorganic N increased from 2014 to 2015 at both sites. While slight changes in mean inorganic N contents were observed at Nyankpala, Kade site showed three times increase in inorganic N from 2014 to 2015. In 2014, amendment application resulted in decreased inorganic N contents compared to the control at Nyankpala. The no input control showed the highest significant inorganic N of 65.2 mg kg−1 and was statistically not different from UREA and AMS treatments. However, at Kade, no statistical differences were observed among the treatments. In 2015, UREA treatment had the highest inorganic N of 117.3 mg kg−1 at Nyankpala and was almost thrice higher compared to the CENT amendment. However, at Kade in the same year, CROT showed the highest inorganic N of 311.8 mg kg−1 while the least was in control. The average TN observed at Kade was two times higher than that of Nyankpala. At Nyankpala, the highest TN of 0.8 × 103 mg kg−1 was observed in AMS treatment, while the least was in control. However, no statistical differences were observed among the treatments at Kade.
Table 5

Soil nitrogen contents following two-season addition of different organic resources in combination with chemical fertilizers

Treatment

Inorganic N (mg kg−1)

At harvest in 2014

Inorganic N (mg kg−1)

At harvest in 2015

Total N (mg kg−1)

At harvest in 2015

Nyankpala

Kade

Nyankpala

Kade

Nyankpala

Kade

CON

65.2 ± 9.6 a

83.2 ± 7.6 a

48.1 ± 1.6 cd

159.6 ± 33.9 c

0.6 × 103 ± 30.2 b

1.5 × 103 ± 50 a

UREA

62.1 ± 2.7 a

108.3 ± 0.6 a

117.3 ± 2.1 a

193.0 ± 56.0 bc

0.7 × 103 ± 0.2 ab

1.6 × 103 ± 0.9 a

AMS

63.7 ± 7.5 a

82.1 ± 25.9 a

89.9 ± 3.8 ab

241.3 ± 17.7 ab

0.8 × 103 ± 120.0 a

1.7 × 103 ± 50 a

CENT

30.4 ± 0.2 b

110.8 ± 12.7 a

42.1 ± 11.8 d

231.1 ± 7.7 abc

0.7 × 103 ± 60.2 ab

1.7 × 103 ± 50 a

CROT

40.8 ± 0.3 b

102.9 ± 9.7 a

53.4 ± 12.4 cd

311.8 ± 37.4 a

0.7 × 103 ± 60.1 ab

1.6 × 103 ± 1.1 a

MZE

40.7 ± 0.9 b

109.9 ± 21.7 a

79.0 ± 24.4 bc

233.9 ± 0.1 abc

0.7 × 103 ± 60.2 ab

1.6 × 103 ± 50 a

Means

50.5

99.5

71.6

288.5

0.7 × 103

1.6 × 103

MSD

15.6

42.3

35.3

81.4

0.2 × 103

0.1 × 103

CV (%)

10.9

14.9

17.4

12.6

9.5

3.1

R2

0.91

0.58

0.89

0.84

0.71

0.50

Different letters (a, b) within the same column indicate treatments with significant differences at P < 0.05

Treatments codes: CON, Control; UREA, CO(NH2)2; CEN, Centrosema pubescens; MZE, Zea mays; AMS, Sulphate of ammonia [(NH4)2SO4]; CROT, Crotalaria juncea; MZE, Zea mays; MSD, minimum significant difference; CV, coefficient of variation

Similarly, soil TOC contents differed significantly (P < 0.05) between sites and among OR treatments in both cultivation years (Table 6). While an increase in mean TOC content was observed at Nyankpala, Kade site showed reduced mean TOC values from 2014 to 2015. Mean TOC content at Nyankpala ranged from 271.3 to 303.1 mg kg−1 and from 377.7 to 325.8 mg kg−1 at Kade site for 2014 and 2015 seasons, respectively. Additionally, Kade site showed higher average TOC and TC contents relative to Nyankpala in both study years. In 2014, AMS and UREA-amended soil at Nyankpala had significantly higher TOC content compared to the other treatments. At Kade, the highest TOC of 450.3 mg kg−1 was observed in UREA treatment but was not statistically different from the other treatments except CROT and control. In 2015, while all treatments significantly (P < 0.05) increased TOC contents compared to control at Nyankpala, no significant differences were observed at Kade. At Nyankpala, the highest TOC of 359.5 mg kg−1 was observed in AMS while lowest values of 261.0 mg kg−1 and 276.6 mg kg−1 were observed in CON and CROT, respectively. Further, mean TC content observed at Kade was twice higher compared to Nyankpala. At Nyankpala, AMS showed the highest TC content and was statistically similar to CENT and MZE. On the other hand, the highest TC at Kade was observed in CENT but was not statistically different from the other treatments except CROT and control.
Table 6

Soil carbon contents following two-season addition of different organic resources in combination with chemical fertilizers

Treatment

TOC (mg kg−1)

At harvest in 2014

TOC (mg kg−1)

At harvest in 2015

Total C (mg kg−1)

At harvest in 2015

Nyankpala

Kade

Nyankpala

Kade

Nyankpala

Kade

CON

266.1 ± 7.6 bc

326.5 ± 41.3 b

261.0 ± 6.0 d

312.4 ± 16.7 a

6.1 × 103 ± 0.1 c

14.8 × 103 ± 0.5 b

UREA

333.9 ± 13.8 a

450.3 ± 26.4 a

325.8 ± 1.7 b

296.7 ± 35.5 a

6.2 × 103 ± 0.1 c

15.3 × 103 ± 0.4 ab

AMS

338.9 ± 13.8 a

369.8 ± 23.7 ab

359.5 ± 3.9 a

347.6 ± 22.2 a

8.1 × 103 ± 0.3 a

15.8 × 103 ± 0.5 a

CENT

173.8 ± 24.3 d

382.3 ± 37.7 ab

295.8 ± 7.9 c

313.8 ± 10.7 a

7.8 × 103 ± 0.2 a

16.1 × 103 ± 0.2 a

CROT

232.9 ± 16.3 c

344.9 ± 34.4 b

276.6 ± 9.3 d

327.7 ± 24.2 a

6.6 × 103 ± 0.4 bc

14.8 × 103 ± 0.1 b

MZE

282.0 ± 21.0 b

392.7 ± 25.4 ab

300.0 ± 7.3 c

356.5 ± 55.6 a

7.3 × 103 ± 0.6 ab

15.8 × 103 ± 0.3 a

Means

271.3

377.7

303.1

325.8

7.0 × 103

15.4 × 103

MSD

48.3

99.1

18.5

94.1

0.9 × 103

1.0 × 103

CV (%)

6.3

9.2

2.1

10.2

4.6

2.3

R2

0.95

0.69

0.97

0.43

0.91

0.80

Different letters (a, b) within the same column indicate treatments with significant differences (P < 0.05)

Treatments codes: CON, Control; UREA, CO(NH2)2; CEN, Centrosema pubescens; MZE, Zea mays; AMS, Sulphate of ammonia [(NH4)2SO4]; CROT, Crotalaria juncea; MZE, Zea mays; MSD, minimum significant difference; CV, coefficient of variation; TOC, total organic carbon

Soil microbial biomass

Treatment application significantly (P < 0.05) altered soil microbial biomass C (MBC) at both sites after harvest (Fig. 2). Average soil MBC at Kade was seven times more than values observed at Nyankpala. At both sites, the average MBC observed for the combined treatments were 2–3 times higher than in the sole chemical N fertilizers. At Nyankpala, soil MBC ranged from 23.8 to 116.2 mg kg−1 for UREA and CROT treatments, respectively. At Kade, however, MBC ranged from 230.0 to 760.0 mg kg−1 for AMS and CROT, respectively.
Fig. 2

Soil microbial biomass C content at Nyankpala and Kade after harvesting. Treatments codes: CON: Control, UREA: CO(NH2)2, CEN, Centrosema pubescens; MZE, Zea mays; AMS, Sulphate of ammonia [(NH4)2SO4]; CROT, Crotalaria juncea; MZE, Zea mays. Different letters indicate treatments with significant differences at P < 0.05

Similar to MBC, two-season repeated treatment application significantly changed the resultant soil microbial biomass N (MBN) at harvest time (Fig. 3). The MBN content for MZE and CROT treatments compared to the sole CFs was 1.5–2.0 times higher at Kade against 2.0–2.4 times at Nyankpala. The CROT-amended soil showed the highest MBN of 68.1 mg kg−1 at Nyankpala and was statistically similar to MZE and CON treatments. The least MBN of 13.7 and 14.5 mg kg−1 were observed in CENT and AMS treatments, respectively. On the other hand, the highest MBN at Kade was observed in CROT treatment and was twice higher compared to AMS. Average MBN at Nyankpala was twice higher compared to Kade. The results of ANOVA are summarized in Table 7. Each factor, i.e., OR treatment, site and year showed significant independent effects (P < 0.05) on grain yield and soil properties, except year on TOC contents. There were significant interaction effects among the factors; OR treatment, site and year, except for non-significant treatment × site on TC and TN as well as year × site interaction on grain yield.
Fig. 3

Soil microbial biomass N content at a Nyankpala and b Kade after harvesting. Treatments codes: CON, Control; UREA, CO(NH2)2; CEN, Centrosema pubescens; MZE, Zea mays; AMS, Sulphate of ammonia [(NH4)2SO4]; CROT, Crotalaria juncea; MZE, Zea mays. Different letters indicate treatments with significant differences at P < 0.05

Table 7

Summary of ANOVA for the effects of contrasting residues on grain yield and soil microbial properties in two sites

Source of variation

Grain yield (t ha−1)

TOC (mg kg−1)

TC (g kg−1)

TN (g kg−1)

CN ratio

Inorganic N (mg kg−1)

MBC (mg kg−1)

MBN (mg kg−1)

BIO CN

ρ-value

ρ-value

ρ-value

ρ-value

ρ-value

ρ-value

ρ-value

ρ-value

ρ-value

TRT

**

**

***

**

**

**

***

***

*

Site

**

**

***

***

**

**

***

***

***

Year

***

ns

**

TRT × site

**

**

ns

ns

*

**

***

***

*

TRT × year

**

**

**

Year × site

ns

**

**

TRT × site × year

**

**

**

TRT treatments, TOC total organic carbon, TC total carbon, TN total nitrogen, MBC microbial biomass C, MBN microbial biomass N, BIO CN ratio of MBC-to-MBN

Significance levels: ***p< 0.001: **p< 0.01: ns = not significant at p > 0.05

Discussion

The extra resource input either in the form of sole CFs or in combination with ORs enhanced maize yield compared to no input control at both sites during the two growing seasons. Average maize grain yield increased up to 170% in the sole CF treatments and up to 200% in the ORs + CF amendments relative to their controls. This result reiterates the need for fertilizer resource additions to increase crop yields in many small-scale crop production systems in SSA (Ncube et al. 2009; Foley 2011; Asante et al. 2017). The ORs with CFs could enhance maize yield not only through the synergy in nutrient release pattern but also as a result of their moisture retention abilities (Bauer and Black 1992; Bationo et al. 2007) compared to the sole chemical fertilization.

The 29% and 21% average grain yield increase in 2015 compared to 2014 for Nyankpala and Kade, respectively is mainly attributed to the residual effects of OR inputs plus the observed relatively high precipitation. This observation implies the possibility of harnessing the residual effects of ORs in soils with high sand proportion unlike the reported no residual effects in sandy soils (Chivenge et al. 2011). Thus, continuous application of ORs with CF is a sustainable approach to improve soil fertility in the Savannah. The observed high AEN in Nyankpala compared to Kade from 2014 to 2015 supports the assertion that soil factors are essential in regulating the effects of fertilizer application and nutrient use efficiency in crop production systems (Mochizuki et al. 2006; Tsujimoto et al. 2017). Hence, the inherent soil fertility is an important consideration for optimum organic and inorganic resource utilization.

Discrepancies in yield response among treatments in both cultivation years are ascribed to the effects of study sites and OR factors. While MZE amendment in combination with CFs appeared to have been suitable at both sites, CENT and CROT showed an inconsistent trend in maize yield at both sites, suggesting different use potentials of ORs of contrasting qualities in different soil ecosystems. Maize grain yield responses in low-quality MZE amendment were comparable to farmers’ conventional chemical fertilization practices although the latter received thrice higher inorganic N inputs than the OR residues. This reflects the importance of OR quality on nutrient availability for plant growth (Palm et al. 2001; Abbasi et al. 2015; Agegnehu et al. 2016). The MZE amendment, given its low N and high CN ratio, decomposes slowly compared to the CROT and CENT with high N and low CN ratio (Palm et al. 2001). Hence, the immediate inorganic N requirement of maize plant at the initial growth period was met by the CF while the MZE complemented subsequent needs. At each year and site, at least one of the OR + CF treatments showed significantly higher AEN than sole CF, in contrast to Chivenge et al. (2011) who observed lower AEN in ORs + N fertilizers treatments compared to sole N fertilizers. In most cases, increased AEN for a particular OR did not correspond with low inorganic N content in the soil. This observation emphasizes the need to identify the best timing of CF application to ORs, taking into account the OR type, soil fertility status and nutrient needs of crops for efficient N utilization.

At Kade, the soil inorganic N was not fully utilized while improved synchrony between nutrient supply and demand happened at Nyankpala. The higher mean maize yield at Nyankpala compared to Kade also supports this assertion. In typical cereal cultivation system in Ghana, compound CFs employing AMS and UREA as top dressing are common fertilization practices. However, OR application combined with CFs are seldom practiced (Partey et al. 2014). Hence, subsequent discussions will compare the broad groups, i.e., sole CF treatments or their combination with ORs with emphasis on litter quality differences. Although the resultant inorganic N contents could be ascribed to the inherent quality composition of the amendments and the N uptake by the plants, the observed inconsistencies between sites also reveals the influence of soil type differences and other climatic variables (Li et al. 2013). This observation implies that the type of OR either sole or combined with CFs could optimally be utilized in specific agro-ecologies for sustainable management of limited soil nutrients in SSA.

The increase in TOC at Nyankpala, compared to a reduction at Kade from 2014 to 2015 is ascribed to the pre-existing TOC stocks which regulated C additions following ORs amendment (Kimetu et al. 2009). Similarly, Chivenge et al. (2011) observed more significant differences in TOC in sandy soils than in clayey and loamy soils. Two seasons of repeated application of AMS fertilizer enhanced soil TOC contents more than the tested ORs at both sites although the latter is predominantly comprised of C. This observation is likely due to the readily available N in AMS fertilizer which triggered the quick growth of competing weeds and upon decomposition added to the soil TOC pool. Studies elsewhere have shown that some weed species are high accumulators of N, phosphorus, potassium, and magnesium (Andreasen et al. 2006; Galal and Shehata 2015), beside their C storage and hence play a significant role on soil nutrient dynamics when left as mulch after weeding.

The different microbial biomass response irrespective of treatment application is likely due to the inherent soil fertility status, along with climatic influences. The relative high soil C fractions at Kade compared to Nyankpala enhanced the growth and population of soil microbes (Bais et al. 2006; Tu et al. 2006), resulting in a higher MBC but lower MBN at Kade. This is likely because the enhanced MBC activity may have caused inorganic N immobilization and subsequent reduction in MBN contents.

The high significant MBC and MBN contents observed in CROT + CF amendment compared to the sole CF application at both sites could connote enhanced soil biological and biochemical improvement (Powlson and Prookes 1987; Fanin et al. 2014). Similarly, Rudrappa et al. (2006) and Gong et al. (2009) reported that organic manure, either alone or in combination with CFs is more effective in enhancing microbial biomass, soil C, and its fractions compared to sole CF applications. As expected, freshly added C components from ORs and CF supplements served as an energy source for soil microorganisms (Palm and Rowland 1997; Wu et al. 2004; Tu et al. 2006; Gentile et al. 2009; Yang et al. 2012). However, the high microbial biomass in CROT amended soil did not necessarily translate into enhanced maize yield. The CF addition to ORs appeared to have masked the effects of freshly added C and N inputs and thus resulted in statistically insignificant differences among the OR + CF amendments. The observed significant interaction effects of treatment and site differences on soil microbial biomass imply different effects of CFs in different soils. In this regard, soil type and fertility status are vital in evaluating the impacts of sole CFs or in combination with ORs on soil microbial biomass dynamics.

Conclusions

Organic residue type combined with CF was found to be an essential factor controlling maize yield, soil organic carbon, and microbial biomass content. This study indicates that low-quality ORs such as maize residue combined with CF shows improved maize yield and enhanced soil properties. High-quality CROT amendment enhanced soil microbial biomass but revealed minimal effects on maize grain yield due to poor synchrony between N release by the residue and uptake by maize plants. While the effects of OR was evident on grain yield and soil nutrients, OR quality differences did not seem to influence microbial biomass significantly. The CF addition to ORs in field conditions tended to mask the effects of freshly added C and N inputs on soil microbial biomass dynamics. There were varying synergies derived from ORs with CF on maize yield, AEN, and soil C and N build up in both agro-ecological zones. Utilization efficiency of applied N differed among treatments and was greater at Nyankpala compared to Kade. Low-quality MZE with CF showed consistent effects on maize yield enhancement in both agro-ecological zones. However, inconsistent responses were observed in the CENT and CROT treatments. The present study provided insights on efficient utilization of ORs for sustainable soil management in specific agro-ecosystems of Ghana. Further efforts should explore the long-term evaluations of these ORs in combination with CF in different agro-ecological zones to identify optimally suitable soil amendments for specific fertility gradients.

Notes

Acknowledgements

The first author is grateful to the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan for providing the PhD study scholarship. We want to thank Agbomadzi Bright of FOHCRE, Kade, Ghana and Edem Halolo of SARI, Tamale, Ghana for their careful management of the experimental fields. Funding was provided by Japan Society for the Promotion of Science (Grant no. 26304024).

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.

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Copyright information

© Society for Environmental Sustainability 2018

Authors and Affiliations

  • Richard Ansong Omari
    • 1
  • Yoshiharu Fujii
    • 2
  • Elsie Sarkodee-Addo
    • 2
  • Yosei Oikawa
    • 2
  • Siaw Onwona-Agyeman
    • 2
  • Sonoko Dorothea Bellingrath-Kimura
    • 3
    • 4
    Email author
  1. 1.United Graduate School of Agricultural ScienceTokyo University of Agriculture and TechnologyFuchuJapan
  2. 2.Institute of AgricultureTokyo University of Agriculture and TechnologyFuchuJapan
  3. 3.Leibniz Center for Agricultural Landscape Research, Institute of Land Use SystemsMüenchebergGermany
  4. 4.Institute of Agriculture and Horticulture, Faculty of Life ScienceHumboldt-University of BerlinBerlinGermany

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