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0International Soil and Water Conservation
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International Soil and Water Conservation Research I (■■■■) Ill-Ill
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Original Research Article
Effects of soil physical properties on soil loss due to manual yam harvesting under a sandy loam environment
Pius Olufemi Olusegun Dada *, Olusegun Rasheed Adeyanju, Olayemi Johnson Adeosun, Johnson Kayode Adewumi
Department of Agricultural Engineering, Federal University of Agriculture, Abeokuta P.M.B. 2240, Abeokuta, Ogun State, Nigeria
ABSTRACT
Soil degradation is a growing problem worldwide because it reduces the fertile top layer of the soil available for food production and one such degradative action is soil erosion due to the harvesting of crops. Soil loss due to crop harvesting with particular reference to yam tubers has not been quantified globally despite the fact that yam is a major staple food consumed worldwide and it is prevalent in many parts of Nigeria. Harvesting yams in our environment is usually done with the soil attached to the yams due to the fact that farmers do not want additional work of removing soil attached to the yams. This study investigates the soil physical properties that influence soil loss due to yam harvesting in Abeokuta, South-Western Nigeria and to assess the quantity of soil loss due to yam harvesting. Based on representative sampling area per location, yam tubers were harvested manually within the entire yam farmland from October to December 2012. Gross weight, net weight and the amount of soil adhering to the yams were measured. Effects of soil physical properties such as soil moisture content, heap bulk density, inter-heap bulk density and soil texture were investigated with respect to soil losses. The results showed that moisture content ranged from 4% to 15%, heap bulk density ranged from 0.93 to 1.29 g cm~3 and inter-heap bulk density ranged from 1.03 to 1.50 g cm~3. They all had a positive correlation with soil loss. Soil particle size analysis for Federal University of Agricultural, Abeokuta (FUNAAB) and Alabata revealed that sand content was (86.78% and 88.32%), clay content (10.69% and 7.6%) and silt content, (2.53% and 4.08%) respectively. Study also revealed that clay content of the soil positively influenced the total soil loss during the yam harvesting. The mean soil losses in Federal University of Agriculture, Abeokuta (FUNAAB) and Alabata village yam farms were 4303 and 2125 kg/ha/harvest respectively. The study also revealed that soil moisture content at harvesting time and clay content are the key factors affecting soil loss due to yam harvesting. Consequently, soil loss due to crop harvesting should be considered in soil erosion control strategies, sediment budget and for better post harvest procedures. © 2016 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Production and Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-
ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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ARTICLE INFO
Article history: Received 5 August 2015 Received in revised form 24 February 2016 Accepted 29 February 2016 Available online 2 March 2016
Keywords: Heap bulk density Manual yam harvesting Soil degradation Soil loss
Soil physical properties
1. Introduction
Soil erosion is the removal of topsoil and in severe cases the
subsoil by water, tillage, or wind. It is often the concern of farmers to maintain the topsoil since the quality of the topsoil is one of the factors affecting the growth of crops. Soil erosion is a growing problem worldwide because it reduces the fertile top layer of many agricultural lands available for food production and studies have shown that more than 99% of the world's food comes from agricultural lands (FAO, 2012).
A major area of soil erosion research which has received little attention is soil lost from farm land during the harvesting of root crops such as sugar beet, potato, carrot, onions, cassava and chicory (Mwango et al., 2015). During the harvesting of some of these crops, soil adhering to the crop, loose soil or clods and stones are exported from the field together with the harvested crop (Ruys-schaert, Poesen, Verstraeten, & Govers, 2004, 2005, 2006). This process of detaching soil from the field where the crops are grown to locations such as markets, farmsteads and crop processing factories is known as Soil Loss During Crop Harvesting (SLCH). Yam
* Corresponding author.
E-mail addresses: dadafemo@yahoo.com, dadapoo@funaab.edu.ng (P.O.O. Dada). Peer review under responsibility of International Research and Training Center on Erosion and Sedimentation and China Water and Power Press.
http://dx.doi.org/10.1016/j.iswcr.2016.02.007
2095-6339/© 2016 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Production and Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
is a tropical crop that has not been fully mechanised in most parts of Africa despite the fact that most of the world production of yam is from Africa (about 96%) with Nigeria alone accounting for nearly 71% (about 37 million tonnes) of the total world yam production (IITA, 2007) and yam production is rapidly declining due to loss of soil fertility.
Soil factors that influence soil loss during harvesting are attributed to texture, moisture content, structure and organic matter level. The shape and roughness of the crop could also influence the soil loss during harvesting operations. There is the possibility that soil loss during harvesting will increase with the size and shape of the tuber crops. Agronomic factors such as plant density and crop yield also have effects on the soil lost. Although SLCH is mostly overlooked in soil erosion and sediment budget studies, Poesen, Verstraeten, Soenens, and Seynaeve (2001) reported that SLCH for sugar beet and chicory roots can vary between a few to tens of mg ha-1 per harvesting event and that soil losses induced by crop harvesting could be of the same magnitude as soil loss by water or tillage erosion and this should not be disregarded in soil erosion control strategies. Soil losses during sugar beet harvesting ranges
between 1.2 to 1.9 t ha 1 yr \
and 0.2 to 0.39 t ha yr"1 for
potato harvesting (Li, Ruysschaert, Poesen, & Zhang, 2006). In a study carried out in Tanzania, soil loses due to harvesting of carrot, onion and potato, were 7100, 3800 and 700 kg/ha/harvest (Mwango et al., 2015) and it was concluded that soil water content during onion harvesting played a major impact on soil loss but for carrot and potato, the effect of moisture content was not significant which can be as a result of time of harvesting or the moisture condition of the soil. A study in Uganda also revealed a soil loss from cassava harvesting with an average of 3400 kg/ha/ harvest (Isabirye et al., 2007) representing a huge amount of soil degradation. Despite the assessment of soil losses in tuber and root crops in many parts of the world, there is very little information on soil losses during manual yam harvesting, the need then arises to embark on this study to evaluate losses of soil from harvested yam fields and investigate the soil physical properties influencing it.
2. Materials and method
2.1. Site description
The experimental sites for this project were situated within the Federal University of Agriculture at Abeokuta (Latitude 7o14' North and Longitude 3o25' East) and Alabata, both in Odeda local Government Area Abeokuta, Ogun State, Nigeria (Fig. 1). Land slope of the locations varied between 2% and 3%. The vegetation is mainly secondary forest. The annual rainfall is 1200 mm. Particle size distribution investigated revealed that the soil texture at both locations was sandy loam. The dominant soil in the study locations is classified as an Alfisol.
2.2. Sample protocol
2.3. Determination of gravimetric moisture content from the yam heaps (GMC)
GMC(%) =
mass of water mass of oven dried soil
2.4. Heap bulk density and interheap bulk density
Bulk density samples from yam heaps and in between heaps were taken from yam fields at depths of 0-10 and 10-20 cm using cylindrical cores 7 cm diameter x 10 cm height (Blake & Hartge, 1986). Each of the samples were transferred into a moisture can, weighed and oven dried at 105 oC to constant weight. Thereafter the samples were reweighed to determine the mass of dry soil. Mathematically, bulk density was calculated using the relation below
„ ,, , i ^ mass of dry soil
Bulkdensity (g/cm3)=—--i-
volume of core (2)
where volume of the soil core sampler (cm3)=jtr2h, where r is radius of soil core and h is the height (cm).
2.5. Particle size distribution
Particle size distribution was determined by Hydrometer method of Gee and Or (2002) to determine the soil textural class of the soil in the yam fields.
2.6. Measurement of plant density (PD) ha
The plant density (PD) ha-1 was computed by multiplying the number of yam plants by 10,000 m2 divided by the Experimental Plot Area (EPA).
PD (ha-i)= numberofyamplants x10, 000. 1 ; EPA
2.7. Determination of average tuber yield (ATY) This was computed as
Average tuberyield(ATY) =
netweight of yams number of yam tubers
2.8. Determination of mass tuber yield (MTY) kg ha 1 harvest 1
This was computed by multiplying the plant density (PD) ha with the Average Tuber Yield (ATY) kg. Therefore,
Mass of tuber yield(MTY) = PD (ha)-1 x ATY ((kg).
Soil samples from the yam fields were taken in the mornings during the harvesting of the yams from the heaps. Twenty different spots at each location were used for sample collection. Yam tubers were carefully dug out of the heaps using small cutlasses and hands after cutting off the yam stems. The tubers are weighed with the soil attached and thereafter the soil adhering to the tubers is scraped off with a light stick and weight of soil and yam tuber measured with a spring balance. The soil samples collected are then packed into polythene bags and sealed for transportation to the laboratory for further investigation.
2.9. Determination of total soil loss due to yam harvesting specific
Total soil loss due to yam harvesting specific TSLYHSpec is di-mensionless (Ruysschaert et al., 2004).
Total SLYHSpec (kgkg-1) =
where Mds= total mass of over-dried soil loss (kg) and Mcrop= net mass of yam tubers (kg).
I-1-1-1-1-1-1-1-1
0 1.25 2.5 5 Kilometers
Fig. 1. Location of yam fields in Abeokuta, Southwest Nigeria.
Table 1
Mean values of soil physical properties.
Location Particle size distribution % Gravimetric moisture content (%) Heap bulk density (g cm 3) Inter-heap bulk density (g cm 3)
Sand Silt Clay
FUNAAB 86.78 2.53 10.69 10.8 1.22 1.45
ALABATA 88.32 4.08 7.6 11.2 1.00 1.27
P <0.05 0.641 0.390 0.110 0.846 0.001 0.046
2.10. Determination of soil loss due to yam harvesting crop (SLYHcrop)
SLYHcrop is the total soil loss for yam on an area-unit basis (kg ha-1 harvest-computed using Eq. (7)
SLCHcrop = SLCHspec xMcy (kgha-1harvest-1) (7)
where Mcy=net crop yield.
2.11. Analysis of experimental result
Experimental results were processed statistically by two-way analysis of variance. The LSD procedure was performed to compare means of computed parameters. Statistical Analysis was carried
out with MINITAB 16.0 statistical package. Strength of linear relationship was determined by correlation analysis to determine the strength of association between variables.
3. Results and discussion
3.1. Soil physical properties
Particle size distribution investigated revealed that the soils in study locations were predominantly sandy loam with mean values of 86.8% sand, 11.1% clay and 2.5% silt for FUNAAB and 88.7% sand, 7.4% clay and 4.1% silt for Alabata respectively. Gravimetric moisture content ranged from 10% to 12% in the study areas. In the
two locations, there was no significant difference in terms of the gravimetric moisture content and with p values 0.85 and 0.51 respectively. This was due to the fact that they were in the same geographical location. Heap bulk density ranged from 1.00 to 1.22 g/cm3 and inter-heap bulk density from 1.27 to 1.45 g/cm3. It was observed that the bulk density was higher in between the heaps than on the yam heaps which can be attributed to no pulverisation of the soil in-between heaps. Significant differences were observed with respect to heap bulk density and interheap bulk density with p values of 0.001 and 0.046 respectively which reveals the strong variation in the structure of the soil at both locations (Table 1).
3.2. Soil loss parameters
Mean soil loss from yam harvesting (specific) was slightly higher in the yam fields located in FUNAAB compared to Alabata with values 0.08 and 0.06 kg kg" 1 though there was no significant difference in the two locations (P < 0.05) (Table 2). Mean value for ten tubers of yam had a weight of 56 kg and 68 kg for FUNAAB and Alabata respectively. Yam tubers in the Alabata location had higher weights than tubers in FUNAAB which might be attributed to lower bulk density observed and the variability of soil nutrient status. The net weight of ten selected yam tubers at Alabata and FUNAAB yam fields showed no significant weight difference (P < 0.05), but there were significant differences in plant density and mass of tuber yield (Table 2). There was also a positive correlation in the soil loss during yam harvesting with respect to moisture content, heap bulk density and inter heap bulk density (Table 3). Soil loss determined for the yam crop ranged from 383 to 7135 kg/ha/harvest with the highest value recorded in FUNAAB despite the high bulk density observed. This was attributed to the
clay content. The mean soil loss for the crop (yam) for FUNAAB was significantly higher than for Alabata with values of 4303 and 2125 kg/ha/harvest respectively (Table 2). The study revealed that at both locations soil loss was significantly high relative to other agents of soil erosion. The soil loss from harvesting was relatively high with respect to other crops like carrot, cassava and onion as reported by (Mwango et al., 2015; Isabirye et al. 2007). Grav-imectric moisture content had a positive correlation with heap bulk density and inter-heap bulk density at both locations, though the relationship was higher for Alabata yam fields relative to FU-NAAB yam fields which further reveals the effect of soil moisture on soil loss (Table 3). The high moisture content in the soil during harvesting aided the amount of soil adhering to the yam surface. There was a strong positive correlation between soil loss and moisture content, heap bulk density and particle sizes (Table 3) revealing that soil physical properties play a significant role in influencing soil loss during harvest periods. Similar reports were established by Li et al. (2006) and Ruysschaert et al. (2006) where soil moisture content had both linear and exponential relationship with soil loss parameters.
4. Conclusions
Soil loss due to yam harvesting was quantified and soil physical properties that influence the huge amount of soil loss was investigated. It can be concluded that a significant amount of soil is lost from manual yam harvesting especially when the soils have a high clay content.. The main factors responsible for the large amount of soil loss during yam harvesting at both fields were soil moisture content and clay content. Additional factors are size and shape of crop. The high soil loss from yam harvesting and other
Table 2
Descriptive statistics of mean values of computed parameters.
Plots Mnet (kg) (ten tubers) Plant density (ha"1) Mass tuber yield (kg ha1 har-1) TSLYHspec (kg kg1) TSLYHcrop (kg ha1 har
FUNAAB 56.02a 10720a 60052a 0.08a 4303a
ALABATA 68.90a 5380b 35536b 0.06a 2125a
F value 0.84 74.30 8.72 0.46 3.62
P <0.05 0.387 0.000 0.018 0.515 0.094
Means with the same letter are not significantly different (P < 0.05).
Table 3
Correlation coefficients of soil physical properties and soil loss.
GMC (kg kg1) HBD (g cm-3) IBD (g cm-3) % Sand % Clay % Silt TSLYS (kg kg-1) TSLYHcrop kg ha-1 har-1)
GMC 1.0 1.0
HBD 0.084 F 0.817 A 1.0 1.0
IBD 0.063 F 0.862 A 0.704 F 0.817 A 1.0 1.0
% Sand 0.001 F 0.998 A 0.054 F 0.872 A -0.021 F 0.954 A 1.0 1.0
% Clay - 0.199 F 0.441 F 0.405 F - 0.814 F 1.0
0. 582 A 0.202 A 0.246 A 0.004 A 1.0
% Silt 0.263 F -0.622 F - 0.466 F - 0.478 F - 0.064 F 1.0
0.463 A 0.55 A 0.185 A 0.162 A 0.860 A 1.0
TSLYS(kgkg-1) 0.441 F 0.233 F 0.069 F 0.706 F 0.620 F 0.199 F 1.0
0.202 A 0.518 A 0.849 A 0.022 A 0.056 A 0.581 1.0
TSLYH crop kg ha1 har-1) 0.250 F 0.492 F 0.401 F - 0.744 F 0.826 F 0.031 F 0.905 F 1.0
0.487 A 0.146 A 0.251 A 0.014 A 0.003 A 0.933 A 0.000 A 1.0
F=FUNAAB, A=Alabata.
tuber crops should not be ignored when assessing soil erosion on agricultural lands.
Acknowledgements
The authors express acknowledgement to the Department of Soil Science and Land Management of the Federal University of Agriculture, Abeokuta for giving access to their Soil laboratory to carry out some soil related experiments. Yam farmers in the various locations are also highly appreciated for giving us access to their yam fields during the harvesting period. They displayed a high level of patience and understanding.
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