Short communication

Amelioration of a heavy clay loam soil with rice husk dust and itse�ect on soil physical properties and maize yield

M.A.N. Anikwe

Department of Agronomy, Faculty of Agriculture, Enugu State University of Science and Technology, P.M.B. 01660 Enugu, Nigeria

Received 5 January 1998; received in revised form 14 December 1999; accepted 5 January 2000

Abstract

Two types of rice husk dust (RHD) with ®ve application rates were tested for their in¯uence on selected soil physical properties

and growth of maize in a heavy clay loam soil. The research was conducted in the 1996 and 1997 farming seasons in a Dystric

Leptosol at Enugu State University Teaching Farm, Abakaliki, Nigeria. Two types of RHD (burnt and unburnt) with ®ve rates of

application (0.0, 1.5, 3.0, 4.5 and 6.0 ton haÿ1) comprising 20 experimental units were set up in the ®eld using split-plots in ran-

domized complete block design replicated four times. The results indicated that neither the seed yield, plant height nor soil physical

properties were a�ected (P < 0.05) by the two types of RHD. However, the two rates of application a�ected seed yield and plant

height of maize at harvest (90 days after planting (DAP)). Similarly, soil dry bulk density, total porosity and penetration resistance

at 48 and 60 DAP were signi®cantly a�ected (P < 0.05) by the treatments, while saturated hydraulic conductivity was a�ected at 90

DAP. The highest average seed yield and plant height of maize were obtained in plots amended with 4.5 tons haÿ1 rice dust. These

were approximately 53% and 22% higher than the control, respectively. Seed yield and plant height of maize increased signi®cantly

with improvement of soil physical properties. The results of the work indicate that RHD applied at 4.5 ton haÿ1 is appropriate to

ameliorate the physical properties of a clayey soil by improving water transmissivity and soil aeration and hence soil productivi-

ty. Ó 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Heavy clay loam soil; Bulk density; Hydraulic properties; Maize yield

1. Introduction

Clay soils are inherently fertile and have high waterholding capacity which enables them to sustain a highlevel of crop production. They have very low perme-ability, thus minimizing seepage losses. They are,therefore, in many respects an ideal soil for arable cropproduction. However, their poor permeability leads towater-logging, drainage and salinity problems with littledrainage water being leached below the root zone(Tanton, 1989). The low permeability and water-loggingproblems make them unattractive for sustainable cropproduction during the wet season. These, combined withhigh compaction rate give rise to low total value of in-®ltration rate, total porosity, hydraulic conductivity andmean weight diameter of soil aggregates (Lal, 1979).

Increase in demographic pressure on land is forcingfarmers to expand production into more marginallands that would not have been previously used for

production. Clay soils, which are commonly avoidedbecause of di�culties in managing them, are now in-creasingly being examined for potential agriculturaldevelopment. There is therefore an urgent need foreconomically viable system of reclamation, if these soilsare to provide sustainable agricultural development(Tanton, 1989).

Rice husks are the largest milling by-products of rice,constituting one-®fth by weight. With world annualpaddy production now over 300 billion kg, over 60 bil-lion kg of rice husks are produced annually (Beagle,1978). Rice husk dust, which is an agro waste aban-doned after rice milling is a potential environmentalpollutant. The problem of rice-mill waste disposal isworldwide (Luh, 1980; Houston, 1992) and the typicalfarm practice in Nigeria is to burn the wastes, resultingin both air pollution and ®re hazards (Omaliko andAgbim, 1983). In South-Eastern Nigeria, large quanti-ties of rice-mill wastes (unburnt and partially burnt)accumulate from the numerous mills and consequently,these wastes have formed arti®cial ``mountains'' occu-pying a considerable portion of arable land (Nnabude,

Bioresource Technology 74 (2000) 169±173

E-mail address: anikwema@enugu.nipost.com.ng (M.A.N. Anikwe).

0960-8524/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved.

PII: S 0 9 6 0 - 8 5 2 4 ( 0 0 ) 0 0 0 0 7 - 9

1995). It has been suggested that rice husk dust (RHD)with high speci®c surface area and organic carboncontent can be used as a soil amendment to improve thephysical properties of the soil. Letey (1977) noted thatwhen large quantities of organic wastes are incorporatedinto the soil they become a signi®cant component of thematrix and can alter pore sizes while Mbagwu andPiccolo (1990) reported decreased apparent density ofstructural aggregates separated from organic waste-amended soils. Similarly, Mbagwu and Ekwealor (1990)found variations in water retention, available water ca-pacity and ®eld capacity for di�erent soils amended withbrewerÕs spent grain.

The potentials of agricultural wastes for soil im-provement have long been recognised in developedcountries (Johnston, 1986) but their e�ect on tropicalsoils where organic matter plays a more important rolein soil productivity, have not been studied extensively.

This work aims at examining the e�ect of di�erenttypes and levels of RHD on the bulk density and hy-draulic properties of a heavy clay loam soil and maizeyield. Speci®cally, the work will be focused on deter-mining if the addition of RHD will reduce the soil bulkdensity, increase water transmissivity and hence soilproductivity.

2. Methods

The experiment was carried out at the research andteaching farm of Enugu State University of Science andTechnology, Abakaliki, Nigeria. The area is locatedwithin latitude 06°40N and longitude 08°650E south-westof the derived savannah zone of Nigeria. Annual rainfallis approximately 1700 mm spread between April andNovember. The site is gently sloping (3±5%). The soil isof shale parent material. It is shallow with unconsoli-dated parent material within 1 m of the soil surfaceclassi®ed as Dystric Leptosol (Anikwe et al., 1999).

The initial soil properties were: bulk density, 1.57 gcmÿ3; total porosity, 41%; pH in water, 5.18; total N,0.14%; organic carbon, 1.53%; extractible Na, K, Mgand Ca were 0.06, 0.23, 1.30 and 2.13 cmol(+) kgÿ1,respectively. Exchangeable acidity and e�ective cationexchange capacity were 0.29 and 4.09 cmol(+) kgÿ1,respectively. Also, the soil consisted of 32% clay, 46%silt and 24% sand. The experiment was conducted dur-ing the 1996 and 1997 farming seasons (April±Novem-ber).

The ®eld was prepared with traditional hoes. A totalland area of 36 m ´ 13 m (468 m2) was marked out forthe experiment. The ®eld was divided into four blocksand each block was further divided into ®ve experi-mental units of 6 m ´ 2 m (12 m2). These were separatedby a one meter alley while the blocks were one meterapart (Fig. 1).

There were a total of 20 experimental units set out inthe ®eld using split-plots in randomized complete blockdesign (RCBD), replicated four times. The types ofRHD were placed on the sub-plots while the rates ofRHD were placed on the main plots (Fig. 1).

Two types of RHD ± partially combusted RHD(burnt RHD) and unburnt RHD ± were applied at therates of 0.0, 1.5, 3.0, 4.5 and 6.0 ton haÿ1. Nitrogen,phosphorus and potassium fertilizers were used assources of inorganic fertilizer and were applied basallyusing band placement. The fertilizers were applied insplit doses at the rate of 84 kg N haÿ1 as urea at 14 daysafter planting (DAP), while at 60 DAP 45 kg N, 45 kgP2O5 and 45 kg K2O haÿ1 were applied.

The RHD collected from Abakaliki rice mill wastedump was spread on the appropriate plots before thebeds were prepared and was later incorporated sevendays before planting during the preparation of the beds.

The maize variety used was Oba Super II hybridvariety. It was planted at two seeds per hole at 5 cmdepth using 75 ´ 25 cm2 spacing. This was later de-creased to one plant per hole two weeks after emergencegiving a total of 55,000 plants per hectare.

The experimental area was kept relatively weed-freeusing traditional hoes throughout the span of the ex-periment. Twenty ®ve plants were randomly selected,tagged and sampled from each plot. The agronomicmeasurements made in each plot are seed yield (tonhaÿ1), plant height (cm plantÿ1), bulk density (g cmÿ3),soil penetration resistance (kg cmÿ3), soil total porosity(%) and soil saturated hydraulic conductivity (cm sÿ1).

Plant height and seed yield were measured at 90 DAPwhile bulk density, total porosity and penetration re-sistance were measured at 8, 28, 48, 60 and 90 DAP.Saturated hydraulic conductivity was measured at 90DAP. All applications and measurements were made ineach season. Bulk density was determined by the coremethod (Blake and Hartage, 1986). Total porosity wascalculated from bulk density data. Saturated hydraulic

Fig. 1. Layout of the experimental plots. Key: A� unburnt RHD,

B� burnt RHD, 1� 0.0 t haÿ1 RHD, 2� 1.5 t haÿ1 RHD, 3� 3.0 t

haÿ1 RHD, 4� 4.5 t haÿ1 RHD, 5� 6.0 t haÿ1 RHD.

170 M.A.N. Anikwe / Bioresource Technology 74 (2000) 169±173

conductivity was determined by the method of McKeague (1978) while penetration resistance was mea-sured with a pocket penetrometer (5 cm cone). The bulkdensity and penetrometer resistance measurements weremade at ®eld capacity water content. Statistical analysisof data collected using analysis of variance for a split-plot design and correlation analysis were carried out

according to the procedure outlined by Steel and Torrie(1980).

3. Results and discussion

The two types of RHD did not statistically a�ect seedyield, plant height and the measured soil physicalproperties (bulk density, total porosity, penetration re-sistance and hydraulic conductivity). However, the dif-ferent rates (levels) of RHD signi®cantly a�ected(P < 0.05) seed yield, plant height, soil bulk density, totalporosity, penetration resistance and saturated hydraulicconductivity (Tables 1±5).

The highest seed yield was observed in plots amendedwith 4.5 ton haÿ1 RHD in both seasons. Seed yield washigher (P < 0.05) than the control by 51% and 53% for1996 and 1997 seasons, respectively.

Table 1

E�ect of di�erent rates of RHD (ton haÿ1) on some crop attributes

RHD (t/ha) Seed yield

(ton haÿ1)

Plant height

(cm/plant)

1996 1997 1996 1997

0.0 1.28 1.31 139 143

1.5 1.61 1.74 137 160

3.0 1.82 1.89 148 164

4.5 2.59 2.76 178 186

6.0 2.49 2.53 176 188

F-LSD (P < 0.05) 0.74 0.86 11.60 19.4

Table 2

E�ect of di�erent rates of RHD on soil dry bulk density (g cmÿ3)

RHD (t/ha) Days after planting

8 28 48 60 90

1996 1997 1996 1997 1996 1997 1996 1997 1996 1997

0.0 1.09 1.14 1.21 1.23 1.41 1.45 1.42 1.44 1.55 1.49

1.5 1.12 1.14 1.15 1.19 1.42 1.42 1.43 1.42 1.52 1.51

3.0 1.08 1.12 1.22 1.21 1.41 1.42 1.41 1.43 1.53 1.47

4.5 1.12 1.09 1.15 1.20 1.26 1.24 1.27 1.26 1.50 1.51

6.0 1.09 1.10 1.18 1.18 1.27 1.22 1.27 1.25 1.52 1.46

F-LSD (P < 0.05) NS NS NS NS 0.086 0.061 0.079 0.093 NS NS

Table 3

E�ect of di�erent rates of RHD on soil total porosity (%)

RHD (t/ha) Days after planting

8 28 48 60 90

1996 1997 1996 1997 1996 1997 1996 1997 1996 1997

0.0 59 57 55 54 47 46 47 46 42 43

1.5 58 57 57 55 47 47 46 47 41 43

3.0 60 58 54 55 47 47 47 46 42 45

4.5 58 60 57 55 53 53 52 53 43 43

6.0 60 59 56 56 52 54 52 53 43 45

F-LSD (P < 0.05) NS NS NS NS 3.41 5.12 3.87 4.28 NS NS

Table 4

E�ect of di�erent rates of RHD on soil penetration resistance (Kg cmÿ3)

RHD (t/ha) Days after planting

8 28 48 60 90

1996 1997 1996 1997 1996 1997 1996 1997 1996 1997

0.0 0.79 0.54 1.15 1.20 2.23 2.15 3.20 3.02 3.15 3.47

1.5 0.73 0.55 1.10 1.21 2.20 2.10 3.21 3.10 3.45 3.40

3.0 0.53 0.57 1.05 1.10 2.17 2.08 2.13 2.77 3.50 3.38

4.5 0.51 0.50 1.00 0.78 2.01 1.85 2.05 2.25 3.50 3.40

6.0 0.57 0.54 1.02 1.05 2.01 1.90 2.03 2.15 3.42 3.40

F-LSD (P < 0.05) NS NS NS NS 0.068 0.19 0.18 0.491 NS NS

M.A.N. Anikwe / Bioresource Technology 74 (2000) 169±173 171

No signi®cant di�erences in seed yield were foundbetween the control (0.0 ton haÿ1) and plots amendedwith 1.5 and 3.0 ton haÿ1 RHD. Similarly, no signi®cante�ect was found between 4.5 and 6.0 ton haÿ1 applica-tion rates. Plant height measurements for the two sea-sons followed a similar trend. The plants, growing inplots amended with 4.5 and 6.0 ton haÿ1 RHD, weresigni®cantly taller than the control by 21±24% at both4.5 and 6.0 ton haÿ1 RHD (P < 0.05). The plots with thehighest plant height and seed yield of maize coincidedwith the plots with the lowest bulk density, penetrationresistance, and high total porosity at 48 and 60 DAP inboth seasons (Tables 2±4). Low soil bulk density, pen-etration resistance and high total porosity may haveincreased root proliferation and hence growth of thecrop. These results agree with Mbagwu (1991) whonoted that reduction in bulk density may increase watertransmissivity, increase root penetration and hence thecumulative feeding area of the crop all of which willtranslate to better yield.

The soil dry bulk density was not signi®cantly af-fected by the treatments at 8, 28 and 90 DAP while therewere signi®cant treatment di�erences at 48 and 60 DAP(P < 0.05). The lowest bulk density at 48 and 60 DAPwas obtained in the plots amended with 4.5 and 6.0 tonhaÿ1 RHD. These were (approximately 12±14%) signif-icantly lower than the control at 48 and 60 DAP in bothseasons. The bulk density of the soil at 8 and 28 DAPwas generally low and was probably because of the e�ectof tillage. As the e�ect of tillage disappeared, and therepacking of the soil set in, the application of RHD at4.5 and 6.0 ton haÿ1 helped in keeping the soil loose,hence the reduction in bulk density of the soil at theserates. The treatments did not signi®cantly a�ect bulkdensity at earlier stages (8 and 28 DAP) because tillagemight have masked the e�ect of the treatments at earlierstages. Tillage seem to exert stronger in¯uence on bulkdensity than the treatments at early stages. No signi®-cant treatment di�erence in bulk density was observed at90 DAP. This was probably because of the breakdownof some of the organic material forming the matrix ofthe soil at later stages or because of increase in soilcompaction by various means at later stages (90 DAP).However, bulk density as a measure of resistance to root

penetration has one limitation, it provides no informa-tion on the continuity of pores or planes of weakness inthe soil.

Soil total porosity measurements follow a similartrend as bulk density (Table 3). Although, higher valuesof total porosity were recorded at 8 and 28 DAP for alltreatments, no signi®cant treatment di�erence wasfound among them indicating that tillage rather than thetreatments caused higher values of total porosity at earlystages. However, the plots amended with 4.5 and 6.0 tonhaÿ1 RHD had the highest soil total porosity (P < 0.05)than other treatments at 48 and 60 DAP. Similarly, soilpenetration resistance was lowest at 4.5 and 6.0 ton haÿ1

RHD application rates at 48 and 60 DAP. This waslower (P < 0.05) than the control (0.0 ton haÿ1) by 10±14% for both seasons at 48 DAP and by approximately25±36% for both seasons at 60 DAP. Although, soilpenetration resistance increased with time due to re-packing of the soil after tillage, the treatments did notshow signi®cant e�ects at 8 and 28 DAP. At 90 DAP soilcompaction by various means may have been responsi-ble for the lack of treatment e�ect. Soil penetration re-sistance is a measure of the soils packing ability. It has avery good correlation with bulk density and appears toprovide a better measure of root extension than bulkdensity (Pierce et al., 1983).

The various treatments a�ected (P < 0.05) the satu-rated hydraulic conductivity at 90 DAP (Table 5). Soilsaturated hydraulic conductivity signi®cantly increasedin plots amended with 4.5 and 6.0 ton haÿ1 RHDcompared to other treatment. This was higher (P < 0.05)than the control by approximately 50±62% for bothseasons. The plots amended with 4.5 and 6.0 ton haÿ1

RHD had higher saturated hydraulic conductivity(P < 0.05) and this coincided with the plots with higherseed yield and plant height of maize. This was speciallyadvantageous since the study soil is a heavy clay loamsoil. Higher conductivity means better water transmis-sivity and hence reduction in water-logging. Lowerconductivity in the control plots, plots amended with 1.5and 3.0 ton haÿ1 RHD, may mean increases in water-logging and hence reduction in physiologic activitywhich may have translated to lower plant height andseed yield in those treatments.

The relationship between seed yield and some de-pendent soil parameters is presented in Table 6. Theresults indicate that all measured soil physical parame-ters correlate positively with the yield of maize. Theaddition of the amendment probably led to structuralmodi®cation which a�ected all the measured soil phys-ical parameters. Similar observations regarding the in-¯uence of structure were made by Mbagwu et al. (1994)and Obi and Ebo (1995). This result emphasize the im-portance of improved soil physical properties to soilproductivity and particularly show that the agronomicvalue of biological wastes should not only be measured

Table 5

E�ect of di�erent rates of RHD on soil saturated hydraulic conduc-

tivity (cm sÿ1) at 90 DAP

RHD (t/ha) Ksat (cm sÿ1) 90 DAP

1996 1997

0.0 0.064 0.057

1.5 0.082 0.096

3.0 0.087 0.096

4.5 0.129 0.150

6.0 0.125 0.154

F.LSD (P < 0.05) 0.038 0.056

172 M.A.N. Anikwe / Bioresource Technology 74 (2000) 169±173

by their ability to supply plant nutrients but also by theirability to improve soil physical properties (Mbagwu etal., 1994).

4. Conclusion

The results of this study indicate that RHD can beused as an amendment to ameliorate the physicalproperties of a clayey soil at the rate of 4.5 ton haÿ1.This assertion stems from the fact that its application atthis rate increased plant height and seed yield of maizerelative to control. Similarly, RHD at 4.5 ton haÿ1 in-creased total porosity, saturated hydraulic conductivity,reduced bulk density, and penetration resistance. Allthese are positive productivity indicators because theyimprove water transmissivity, soil aeration and micro-bial activity in a clay soil. More studies of the dynamicsof RHD in the soil should be carried out to con®rmthese results.

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Table 6

Relationship between seed yield (Y) and some dependent soil parameters (x)

Dependent soil parameter Regression model Coe�cient of correlation

Bulk density (g cmÿ3) at 48 DAP Y � ÿ0:152 x� 1:04 0.92�

Bulk density (g cmÿ3) at 60 DAP Y � 0:144 x� 1:072 0.93�

Total porosity (%) at 48 DAP Y � 5:504 x� 38:29 0.93�

Total porosity (%) at 60 DAP Y � 5:752 x� 37:39 0.90�

Penetration resistance (kg cmÿ3) at 48 DAP Y � 1:90 xÿ 1:73 0.82�

Penetration resistance (kg cmÿ3) at 60 DAP Y � 0:438 xÿ 1:74 0.91�

Saturated hydraulic conductivity (cm sÿ1) at 90 DAP Y � 0:0297 x� 0:045 0.91�

* Signi®cant at P < 0.05.

M.A.N. Anikwe / Bioresource Technology 74 (2000) 169±173 173