~ / ~ ~ 9 ( 1 ) (2007) : 51-56

Sugarcane Yield Predict ion in Degraded Sandy Soil Amelioration

ROCHANA T A N G K O O N B O R I B U N l*, SAWAENG R A U Y S O O N G N E R N 2, PATMA VITYAKON 2 and BUNYONG T O O M S A N 3

1Fertilizer Technology Centre, Thailand Institute of Scientific and Technological Research, Phathumthani, Thailand

2Department of Land Resources and Environment, Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

~Department of Agronomy, Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand

ABSTRACT

The relationship between soil properties and sugarcane growth parameters can be determined sugarcane yield of banding application in degraded Korat sandy soil series (Oxic Paleustults). The agronomic traits affecting cane yield can be arranged in descending order from tiller density, stool density, stalk length, germination and plant height, respectively. Cane yield (t ha -z) = -59.29 + 0.14 (tiller density) + 0.31 (stalk length); r 2 = 0.90**. The soil properties affected to tiller density and stalk length were organic matter and available phosphorus. Hence, the factors should be collected for sugarcane yield prediction in degraded sandy soil amelioration were tiller density, stalk length, organic matter and available phosphorus which can reduce cost of data collection and soil analysis with high accuracy result.

Key words : Sugarcane, yield prediction, degraded sandy soil

I N T R O D U C T I O N

Soil degradation is the temporary or permanent lowering of the soil productivity (Scherr, 1999, UNEP, 1992). Degradation processes include erosion, compaction, hard setting, acidification, declining soil organic matter, soil fertility depletion, biological degradation and soil pollution (Lal and Stewart, 1990). The expansion of sugarcane plantation area on unsuitable land with monoculture was main reason for s0il degradation. In addition, many soils in Northeast Thailand genesis over deeply weather regolith on diverse rock types or on colluvium originating cause of mainly low activity clay mineral (kaolinite) in soil (Kanket, 2002) is inherently very low in physical properties and soil fertility. The organic cycle is interrupted by cultivation and by moving nutritional plants from the fields, the balance between inorganic and organic soil constituents is disturbed. The soil consistency decreases and erosion with its consequences occur. Nevertheless, the

*Author for Correspondence e-mail: t_rochana@hotmail.com

new high yield varieties need greater fertilization with inorganic fertilizers that cause higher activity of micro-organism in the soil. These need carbon as a source of energy, so the degradation of soil organic matter is accelerated and should be supplemented by organic materials regularly. An alternative approach to increasing nutrient retention properties where addition of high-activity clay has been shown to permanently increase the CEC of the soil and provide positive yield benefits (Noble et al., 2001, 2003, 2004). Clay soil (montmorillonite) was considered as soil conditioner which has molecular sieving and high cation absorption properties.

In this study, organic material (filter cake, cattle manure and bagasse) and clay material (2:1 montmorillonite clay) were banded amendment with the aim to improve soil properties and cane yield. Otherwise, relationship between soil properties that can be improved by amendment materials and sugarcane growth index can use to determine the appropriate material for soil amelioration.

52 ~u~v~ ~ec~

M A T E R I A L S AND M E T H O D S

Experimental site

The study site was located in Kuchinarai district, Kalasin province in Northeast Thailand with loamy sand texture of Korat soil series (Kt: Oxic Paleustults, fine-loamy, siliceous). The main character of Korat series in this site has 5.56, available phosphorus 20.45 ppm, exchangeable potassium 0.14 cmolc kg -~, 0.79 cmolc kg -~ of calcium, 0.26 cmolc kg -~ of magnesium, 0.43% of organic matter and cation exchange capacity 4.33 cmolc kg -~.

Experimental method

The effect of organic materials i.e. cattle manure @ 25 t ha -j, filter cake @ 50 t ha ~ and bagasse @ 12.5 t ha ~ and clay soil (montmorillonite) @ 25, 50 and 75 t ha 1 on soil properties, sugarcane growth using banding of materials in the furrow. Plot size was 115.2 m 2 (8 rows, 1.2 meter spacing width and 12 meter length). The banding of materials was done after furrow and basal application of chemical fertilizer@ 25-25-12.5 kgN- P20;K20 ha -j was put in the furrow. This trial was laid on randomized complete block design (RCBD) with four replications. The diseases, pest, drought and infertile soil tolerance variety selected is Kanchanaburi 88-92.

Data collection

Soil samples were collected in 6 middle rows and 12 meter length of each sub-plot in banding trial. Samples were collected from two levels of soil depth (0-30 cm and 30-60 cm) at three positions of sub-plot and then composite sample for each depth. Undisturbed soil samples with 2 replications in each plot collected for determined physical properties. Air dried of disturbed soil and sieved (2 mm) were used to analyse chemical properties. Soil samples were collected after planting in four months interval. Soil analyses were done for physical and chemical properties as bulk density was measured using core method (Brady, 1984), particle size distribution using pipette method (Dewis and Freitas, 1970), soil moisture using gravimetric method (Gardner, 1956), aggregate stability using wet sieving method (Black, 1965a), soil reaction was measured as pH (1:5 H20 ) using pH meter (Black, 1965b), available phosphorus using BraylI method and measured by spectrophotometer (Bray and Kurtz, 1945), exchangeable potassium, calcium and magnesium commonly used ammonium acetate pH 7 extraction and estimated using flame emission (Jackson, 1958; Chapman and Pratt, 1982) and atomic absorption spectrophotometry (AAS) (Jackson, 1958; Chapman and Pratt, 1982; Watson and Isaac, 1990; Wright and Stuczynski, 1996), organic matter was determined using wet oxidation method of Walkley and Black (Black, 1965b), cation exchange capacity (CEC) using Metson method (Peech, 1945).

Sugarcane growth data were collected in parameters viz., germination was estimated by counting the total buds

germinated against number of sett planted at 35 days after planting and calculated in per centage of germination = (Number of shoot per row / Number of sett planted per row) x 100, tiller density were counted in unit area and expressed as tiller per hectare = (number of tiller / Plot size (m 2) ) x 10,000, stool density was count number of stools in each sub-plot and converted to stool per hectare = (number of stool / Plot size (m2)) x 10,000, number of stalk per stool and primary stalk height were collected in selected stool (once in middle of every row), six stalk samples were taken from outer two rows for measured stalk length, stalk diameter, stalk weight, brix and commercial cane sugar (C.C.S.). The commercial cane sugar was calculated by using the formula % Fiber = (Dry weight after washed / Fresh weight before wash) x 100 and C.C.S. = '((3xPol)/2)x(1-((fiber+5)/100))-brix(1-((fiber+3)/100)). Millable stalks were recorded in each plot and expressed as millable stalks per hectare = number of stalk / Plot size (m 2) x 10,000, yield data was collected in middle six rows and 12 meter length (86.4 m 2) = weight of cane per plot / Plot size (m 2) x 10,000, sugar yield was estimated from C.C.S. and cane yield using formula = (C.C.S. x cane yield (t ha-~))/100.

Data analysis

The relationship between soil properties and sugarcane growth index (millable cane stalk, cane yield and sugar yield) in 32 numbers were determined by statistic package SPSS l 1.0 for windows. The regression model was used stepwise method for simulation by SPSS 11.0 for windows.

R E S U L T S AND D I S C U S S I O N

The bulk density did not differ among treatments at both soil depths after amelioration. The trends of bulk densities at 0-30 cm after banding with organic materials (filter cake, cattle manure and bagasse) were lesser than control. At 30-60 cm soil depth, only cattle manure applicant had lesser bulk density than control. The decreasing of bulk density at 0-30 cm soil and increase at 30-60 cm was caused by tillage effect with the approximate incorporation depth being only 30 cm making the soil loose at 0-30 cm and compact at 30-60 cm. Furthermore, in this trial we found the negative correlation between bulk density and organic matter as shown in Table 1 (r = -0.40*). The increasing of organic matter can reduce soil bulk density as the state organic matter supplied directly, or indirectly through microbial action, the major soil aggregate-forming cements, and increases both air and available content in sandy soils (Miller and Roy, 1990).

Particle size distribution after banding did not show significant differences between treatments at both soil depths. Clay fraction at 0-30 cm soil was not increase after amelioration with organic and clay materials. The increase of clay fraction found at 30-60 cm soil, especially in clay soil and organic materials (more than chemical fertilizer and control by 1-5 per

Sugarcane yield prediction in degraded sandy soil amelioration 53

cent). This was caused by the banding application at the base o f furrow (about 30 cm depth) so more clay content at 30-60 cm depth. However, the most increment o f clay fraction was in bagasse, cattle manure and c lay soil @ 50 t ha -j. This shows that the organic matter can attract c lay part icle p romote aggregate stability by reducing wettability and swelling. Some o f the organic mater ia l s are inherent ly hydrophob ic or dehydrate, so that the organo-clay complex may have a reduced affinity for water. Some inorganic materials can also serve as cementing agents as found in clay material amelioration. Cohesiveness between clay particles is, in fact, the ultimate internal binding force within microaggregates (Hillel, 1998).

The soil moisture is a parameter which fluctuates with rainfall. Only at 30-60 cm soil at 4 and 8 months after planting the mois ture o f soil was s i gn i f i c an t l y di f ferent among treatments. The highest moisture was measured in bagasse application, caused mainly by the high fiber content in bagasse which can hold more moisture in soil during rainy season but quickly loses during drought season. However, at harvest (12 month) the soil moisture in clay soil, filter cake and cattle manure plots increased higher than control at both soil depths. The organic materials can improve moisture-retaining properties o f sandy soils (Stevenson, 1994).

The mean weight diameter, degree o f aggregation and aggregate stability did not differ at both soil depths after banding with various ameliorants. This was caused by non incorporation o f amliorants, hence no more surface area for attachment with soil particles for cementing agent with low binding force. However, after ameliorat ion with organic and clay material the MWD, degree o f aggregation and aggregate stability were higher than control and conventional fertilizer application. Organic matter in sandy soils was protected by adsorption to clay minerals or encrustation by clay minerals

(Hassink et al., 1993). F rom this trial we found posit ive correlation between M W D and degree o f aggregation (r = 0.80**) (Table 1).

The pH of soil (1:5 H20 ) was significantly different among treatments after ameliorat ion at both soil depths. Futhermore,

there were increasing trend at 0-30 cm after banding with clay soil @ 75 t ha j and bagasse due to high calcium content in

these material with 37.44 and 37.50 cmolc kg ~ respectively.

The adsorbed acidic aluminium ions are replaced with calcium ions from the lime; the released H + are neutralized by the carbonates or hydroxides added as lime (Miller and Roy, 1990).

However, the pH o f soil decreased at 12 months after planting in all treatments especially in control and conventional fertilizer except in clay soil @ 75 t ha -l. This shows that clay soil can

increase pH of soil by calcium in its component. From banding experiment we found the relationship between pH and clay

fraction (r = 0.41"), pH with calcium, magnesium and CEC in

soil (r = 0.85"*, 0.50** and 0.72** respectively) (Table 1).

The electrical conductivity in all treatments increased after planting sugarcane especial ly at 0-30 cm soil. The levels o f electrical conductivity were not toxic for sugarcane planting.

The maximum increase o f electrical conductivity was recorded in cattle manure applicat ion where its electrical conductivity

was highest. The increase o f electrical conductivity in all treatments were due to potassium increase as the relationship with r = 0.64** (Table 1). The increase o f cation in soil solution

or activity o f the cation influenced increased conductivity o f soil solution (Foth and Ellis, 1996). From this trial there was a

positive relationship between electrical conductivity with soil moisture (r = 0.47**) showing that more soil moisture can

solute more cation into the soil in available form (Foth and Ellis, 1996).

Table 1: Relationship between physical and chemical soil properties in banding trial

BD MWD DEGREE STATE MOIS %sand %silt %clay pH EC OM P K Ca Mg CEC BD 1 0.15 0.12 -0.02 -0 .10 -0.22 0.24 0.20 0.08 MWD 0.15 1 0.80** 0.29 0.08 -0.31 0.39* 0.21 0.08 DEGREE 0.12 0.80** 1 0.04 0.27 -0.26 0.31 0.18 0.03 STATE -0.02 0.29 0.04 1 -0.24 -0.14 0.14 0.12 0.08 MOIS -0.10 0.08 0.27 -0.24 1 -0.32 0.32 0.31 0.03 %sand -0.22 -0.31 -0.26 -0.14 -0.32 1 -0.97 -0.97** -0.38* %silt 0.24 0.39* 0.31 0.14 0.32 -0.97** 1 0.88** 0.33 %clay 0.20 0.21 0.18 0.12 0.31 -0.97** 0.88** 1 0.41 pH 0.08 0.08 0.03 0.08 0.03 -0.38* 0.33 0.41 1 EC 0.01 0.49** 0.46* -0.12 0.47* -0.39* 0.43* 0.32 0.17 OM -0.40* 0.24 0.26 0.11 0.29 0.07 -0 .05 -0 .09 0.04 P -0.19 0.11 0.09 0.01 0.16 0.15 -0 .13 -0.16 -0.02 K 0.02 0.47 0.42* 0.26 0.17 -0.36* 0.35* 0.35* -0.09 Ca -0.07 0.07 0.01 0.05 0.10 -0.17 0.16 0.17 0.85** Mg 0.16 0.17 -0.07 0.09 0.20 -0.58** 0.52** 0.62** 0.50** CEC -0.11 0.16 0.14 0.34 0.10 -0.29 0.22 0.34 0.72**

0.01 -0.40* -0.19 0 . 0 2 -0 .07 0 . 1 6 -0.11 0.49** 0.24 0 .11 0.47* 0.07 0.17 0.16 0.46* 0.26 0 .09 0.42* 0.01 -0 .07 0.14 -0.12 0.11 0.01 0.26 0.05 0.09 0.34*

0.47** 0.29 0.16 0.17 0.10 0.20 0.10 -0.39* 0.07 0 .15 -0.36* -0.17 -0.58** -0.29 0.43** -0.05 -0.13 0.35* 0.16 0.52** 0.22 0.32 -0.09 -0.16 0.35* .0.17 0.62** 0.34 0.17 0 .04 -0.02 -0 .09 0 .85 0.50** 0.72

1 0.40 0 .23 0.64** 0.30 0.35* 0.20 0.40* 1 0.55** 0.26 0.24 0.04 0.37* 0.23 0.55 1 0.18 -0.03 0.22 -0.02

0.64** 0.26 0.18 1 -0.12 0.32 0.15 0.30 0 .24 -0.03 -0.12 1 0.36* 0.67**

0.35* 0.04 0.22 0.32 0.36* 1 0.21 0.20 0.37* -0.02 0 .15 0.67** 0.21 1

* Correlation is significanrat the 0.05 level, ** Correlation is significant at the 0.01 level

54

The organic matter content at both soil depths increased in all treatments at 12 months after planting but before that it fluctuated. However, the organic matter in soil was differed among treatments only at 30-60 cm soil. The application clay soil @ 50 t ha "a, bagasse @ 12.5 t ha" and clay @ 75 t ha" had maximum organic matter at 30-60 cm soil. Organic matter in sandy soils was protected by adsorption to clay minerals or encrustation by clay minerals (Hassink et al., 1993). From banding trial we found the positive correlation between organic matter and CEC in soil (r = 0.37*) (Table 1).

Available phosphorus increased in all treatments except control. The high available phosphorus found in filter cake, bagasse and clay soil @ 75 t ha t. The filter cake composed with the highest phosphorus content when compare with other ameliorants. There was positive correlation between available phosphorus and soil organic matter content (r = 0.55**) as found by earlier workers (Weir and Soper, 1963; Levesque and Schnitzer, 1967; Levesque, 1969; Sinha, 1971).

Exchangeable potassium at both soil depths slightly increased with the maximum value in cattle manure application. The cattle manure composed with the highest potassium content when compare with other ameliorants. However, bagasse and clay soil amelioration also showed higher exchangeable potassium than chemical fertilizer and control. From this trial we found the relationship of exchangeable potassium with clay fraction (r = 0.35*) (Table 1). The potassium ions are attached between layers of clay crystals by the same negative charges responsible for the intemal adsorption of these and other cations (Brady, 1984).

Exchangeable calcium in soil increased after organic and clay materials application especially at 4 months after planting. The highlight of increment was found in clay soil at the rate of 75 t ha t application where calcium increased at both soil depths after planting 4 months. With high CEC in clay material it can absorb more cation than other ameliorants as relation illustrated in this trial between CEC and calcium in soil with correlation

coefficient 0.67** (Table 1). Any electrically charged colloidal surface area will attract mobile substances of opposite charge in the soil water. Cation exchange sites hold Ca 2+ ion and slow its losses by leaching (Miller and Roy, 1990).

Exchangeable magnesium in soil was quite stable when compare with control and chemical fertilizer where the values decreased. However, the application of filter cake, clay soil @ 75 t ha" and bagasse increased exchangeable magnesium. There was a positive correlation between magnesium and clay fraction (r = 0.62" *) (Table 1). The source of negative charge on silicate clays associated with oxygens and hydroxyl groups exposed at the broken edges and flat external surfaces of minerals. The presence of surface and broken-edge OH groups gives the clay particles their electronegativity and their capacity to adsorb cations (Brady, 1984). Cation exchange capacity increased in organic and clay material amelioration in banding trial. Especially, clay soil application at the rate of 75 t ha ~ has had highest CEC at both soil depths due to high CEC in clay soil with 62.74 cmolckg t . The CEC was related with organic matter and pH of soil with correlation coefficient 0.37* and 0.72** respectively (Table I). Organic matter contributes to the cation exchange capacity, often furnishing 30-70 percent of the total amount. The large available surfaces of humus have many cation exchange sites that adsorb nutrients for eventual plant use (Miller and Roy, 1990). Increasing acidity is associated with decreasing CEC, decreasing supply of available essential plant nutrients and an increase in the amount of solution H + and A13+ (Foth and Ellis, 1996).

The relationship between soil physical properties and growth parameters are presented in Table 2. Negative correlations were found between (mean weight diameter) MWD and stool density (r = -0.40"*), degree of aggregation and stool density (r = -0.38"), aggregate stability with stool density, tiller density, millable cane, cane yield and sugar yield (r = - 0.43 * *, -0.44* *, -0.38" *, -0.41 ** and -0.36' * respectively), %sand content with number of tiller per stool and CCS (r = -

Table 2: Relationship between physical soil properties and growth parameters in banding trial Stool Tiller Millable Cane Sugar

Germination density density Tiller/stool Height Length Diameter Weight Brix CCS Pol Fibre Purity cane yield yield

BD 0.12 0.10 0.08 -0.04 0.01 -0.01

MWD -0.22 -0.40* -0.13 0.27 0.26 0.04

Degree -0.28 -0.38* -0.20 0.20 0.26 0.17

State -0.25 -0.43** -0.44** 0.32 -0.02 -0.26

Mois -0.30 -0.15 -0.07 0.08 0.08 -0.02

%sand 0.37* 0.38* 0.34 -0.45** 0.06 0.33

%siit -0.31 -0.34 -0.27 0.39* -0.08 -0.28

%clay -0.41" -0.39* -0.39* 0.49** -0.05 -0.36*

-0.05 0.21 -0.07 -0.27 -0.16 0.17 -0.23 0.09 -0.01 -0.06

-0.18 -0.10 -0.18 0.10 0.07 0.02 0.14 -0.18 -0.08 -0.05 r

-0.16 -0.04 -0.12 0.02 0.09 0.16 0.09 -0.22 -0.10 -0.10

0.21 -0.04 -0.05 0.07 -0.10-0.13 0.17 -0.38** -0.41"*-0.36**

0.26 0.32 -0.01 0.23 0.23 0.09 0.29 -0.24 -0.01 0.05

-0.21 -0.08 0.19-0.35*-0.21 0 .21 - 0 . 3 1 0.36* 0.30 0.22

0.11 0.03 -0.21 0.41" 0.26 -0.23 0.39* -0.29 -0.24 -0.14

0.30 0.13 -0.15 0.26 0.15 -0.18 0 . 2 1 -0.41" -0.35* -0.29

* Correlation is significant at the 0.05 level ** Correlation is significant at the 0.01 level

Sugarcane yield prediction in degraded sandy soil ameliorat ion 55

Table 3: Relationship between chemical soil properties and growth parameters in banding trial Stool Tiller Millable Cane Sugar

Germination density density Tiller/stool Height Length Diameter Weight Brix CCS Pol Fibre Purity cane yield yield

pH 0.10 -0.07 0.06 0.08 0.20 0.04 -0.24 -0.31 0.06 0.20 0.10 -0.26 0.19 0.13 0.10 0.15

EC -0.29 -0,17 0.12 0.00 0.45** 0.05 -0.16 0.11 -0.33 0.09 -0.09 -0.33 0.18 -0.07 0.15 0.18

OM -0.10 -0.25 -0.11 0.00 0.40* 0.06 -0.08 -0.14 -0.27 0.16 0.02 -0.14 0.26 -0.07 0.06 0,09

P -0,15 -0.20 0.06 0,03 0.63** 0.36* -0.08 0.21 -0.36* -0.09 -0.04 -0.13 0.05 0.05 0.25 0.24

K -0.47** -0.41" -0.20 0,38* 0.33 -0.12 0.14 0.18 -0,25 0.18 -0.34 -0.35* -0.08 -0.40* -0.14 -0.14

Ca 0.15 0.00 0.20 -0.16 0.17 0.06 -0.27 -0.29 0.05 0.19 0.03 -0.22 0,20 0.24 0.21 0.25

Mg -0.34 -0.31 -0.09 0.39* 0.06 -0.26 0.24 0.23 -0.18 0.06 -0.02 -0.36* 0.09 -0.25 -0.12 -0,08

CEC 0,05 -0.17 -0.16 0.07 0.27 0.01 -0.04 -0.31 -0.09 0.26 -0.09 -0.24 0.11 -0.04 -0.07 -0.04

* and ** correlation are significant

0.45** and -0.35"), %clay content with germination, stool density, tiller density, stalk length, millable cane and cane yield (r -- -0.41 *, -0.39", -0.36", -0.41 * and -0.35* respectively). Positive correlations were found between %sand content with germination, stool density and millable cane (r = 0.37", 0.38" and 0.36* respectively), %silt content with number of tiller per stool, CCS and purity (r = 0.39", 0.4 l* and 0.39* respectively) and %clay content and number of tiller per stool (r = 0.49*).

The relationship between soil chemical properties and growth parameters are presented in Table 3. Negative correlation was found between available phosphorus and brix (r = -0.36"), exchangeable potassium with germination, stool density, fiber and millable cane (r = -0.47"*, -0.41", -0.35* and -0.40*) and exchangeable magnesium and fiber (r = -0.36*). Positive correlations were found between EC and tiller height (r = 0.45" *), organic matter and plant height (r = 0.40"), available phosphorus and plant height (r = 0.63"*), exchangeable potassium and number of tiller per stool (r = 0.38*) and exchangeable magnesium and number of tiller per stool (r = 0.39*).

The agronomic traits affecting cane yield i.e. tiller density, stool density, stalk length, germination and plant height, respectively. Serivichayaswadi et al. (1997) stated that the most effective of agronomic trait on cane yield was tiller density followed by stalk length and stalk diameter respectively. The above relationships were used to simulate the model for cane yield prediction using stepwise regression analysis as in models below.

Cane yield = 2.04 + 0.18 (tiller density)

; r a = 0.83**

Cane yield =-59.29 + 0.14 (tiller density)

+ 0.31 (stalk length)

; r 2 = 0.90**

The soil properties affected to tiller density and stalk length were organic matter and available phosphorus. Hence, the factors should be collected for sugarcane yield prediction in soil amelioration were tiller density, stalk length, organic matter and available phosphorus which can reduce cost of

at the 0.05 level and 0.01 level, respectively

data collection and soil analysis with high accuracy result. Otherwise, the appropriate material for degraded sandy soil improvement can be determined by the increasing of tiller density, stalk length, organic matter and available phosphorus. In this trial, filter cake most suited for banding application followed by cattle manure and clay soil @ 75 t ha" respectively.

C O N C L U S I O N

The relationship between soil properties and growth parameters can be determined sugarcane yield after soil amelioration. The factors should be collected for simulate sugarcane yield prediction model i.e. tiller density, stalk length, organic matter and available phosphorus. In this trial, filter cake was suited for banding application followed by cattle manure and clay soil @ 75 t ha ~ respectively.

A C K N O W L E D G E M E N T

The authors wish to thank Mitr Phol Sugar Co., Ltd. for support and staff of Department of Land Resources and Environment for their kind help.

R E F E R E N C E S

Black, C.A. (1965a). Method of Soil Analysis. Part 1 : Physical Soil Properties, American Society of Agronomy

Black, C.A. (1965b). Method of Soil Analysis. Part 2: Chemical and Microbiological Properties, American Society of Agronomy

Brady, N. C. (1984). The Nature and Properties of Soils. Macmillan publishing Co., Inc. 750 p.

Bray, R.H. and Kurtz, L.T. (1945). Determination of total, organic and available forms of phosphorus in soil. Soil Sci., 59: 28-34.

Chapman, H. D. and Pratt, P. (1982). Method of Analysis for Soils, Plants, and Water. Priced Publication 4034, Berkley. University of Califonia, Division of Agricultural Sciences.

Dewis, J. and Freitas, E (1970). Physical and Chemical Methods of Soil and Water Analysis. Food and Agriculture Organization of the United Nations, Rome. 275 p.

Fotll, H. D. and Ellis, B.G. (1996). Soil fertility. 2nd ed. Australia: CRC Press, Inc.

[assink, J., Bouwman, L.A., Zwart, K.B., Bloem, J. and Brussaard, L. (1993). Relationships between soil texture, physical protection of organic matter, soil biota, and C and N mineralization in grassland soils. In Brussaard, L. and M. J. Kooistra (eds.), Int. Workshop on Methods of Research on Soil Structure/Soil Biota Interrelationships. Geoderma 57:105-128.

[illel, D. (1998). Environmental Soil Physics. Academic Press. London, UK. 771 p.

aekson, M. L. (1958). Soil Chemical Analysis. Englewood Cliffs, N J: USA.

[anket, K., Suddhiprakarn, A., Kheoruenromne, I. and Gilkes, R.J. (2002). Clay Mineralogy of some Thai Ultisols. Symposium no. 28, paper no. 2112. Soil Science Symposium, Thailand. 2112- 1 - 2112-8 pp.

al, R. and Stewart, B.A. (1990). Soil degradation. Vol. 11 Advances in soil science. New York, USA: Springer-Verlag.

liller, R. W. and Roy, L.D. (1990). Soils: an introduction to soils and plant growth. New Jersey: Prentice-Hall, Inc.

Ioody P., Ruaysoongnern, S., Guodoa, Liu, Zhiping, Qi and Berthelson, S. (2003). Quantification of Soil Chemical Degradation and Its Remediation in Tropical Australia, China and Thailand. Pedosphere 13(1).

[oble, A. D., Gillman, G. P., Nath, S. and Srivastava, R. J. (2001). Changes in the surface charge characteristics of degraded soil in the tropics through the addition of beneficiated bentonite. Australian J. of Soil Research. 39:991-1001.

�9 Ruaysoongnern, Penning de Vries, F. W. T., Hartmann, C.

and Webb, M. J. (2004). Enhancing the agronomic productivity of degraded soils in North-east Thailand through clay-based interventions. In Water and Agriculture (Eds. V. Seng, E. Craswell, S. Fukai and K. Fischer). ACIAR Proceedings No. 116:147-160.

Peech, M. (1945). Determination of exchangeable cations and exchangeable cations and exchange capacity os soils rapid micromethod utlizing centrifuge and spectrophotometer. Soil Sci., 59: 25-48.

Seherr, S. J. (1999). Soil Degradation: A Threat to Developing- Country Food Security by 2020. International Food Policy research Institute, Washington, DC. Food, Agriculture, and the Environment Discussion paper 27. 63 pp.

Seriviehayaswadi, P., Sirasoontorn, S. and Chatwachirawong, E (1997). Yield and Yield components Relationship in Sugarcane. KasetsartJ. (Nat. Sci.). 31:20-27 (in Thai with English abstract).

Stevenson, F. J. (1994). Humus chemistry: genesis, composition, reactions. 2nd ed. John Wiley & Sons, Inc. New York, NY. 496 p.

Watson, M. E., and Isaac, R. A. (1990). Analytical instruments for soil and plant analysis. In Westerman, R. L. (Ed.). Soil testing and plant analysis. (pp. 691-740). Madison, WI, USA: Soil Science Society of America.

Wright, R. J. and Stucznski, T. L (1996). Atomic absorption and flame emission spectrometry. In Sparks, D. L. (Ed.). Methods of soil analysis, Part 3, chemical methods, SSSA Book Series No. 5. (pp. 65-90). Madison, WI, USA: Soil Science Society of America.

Received Dec. 28, 2006; Revised Feb. 15, 2007; Accepted March 14, 2007