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Effects of trench planting and soil chiselling on soil properties and citrus production in hilly ultisols of China
soila Tillage Research
Soil & TillaLge Research 43 (1997) 309-318
ELSEVIER
Effects of trench planting and soil chiselling on soil properties and citrus production in hilly ultisols of China Jun Lu a,*, M.J. Wilson b, Jinyan Yu a a Department
of Soil Science and Agrochemistry. Zhejiang Agricultural b Diuision of Soils, Macauluy Land Use Research Institute,
University, Hangzhou Aberdeen AB15 8QH,
310029, UK
China
Accepted 1 May 1997
Abstract Trench planting and soil chiselling are special techniques of soil utilization and reclamation for citrus production in the hilly red soil region of China. Serious erosion, acidity, compactness, low fertility, and seasonal drought are major problems in this region. These problems in the red soil (i.e., ultisol in US taxonomy system) limit plant production, especially that of deeply rooting plants. Trench planting was aimed at improving the entire rooting space for the citrus tree growth before the citrus saplings are transplanted to the red soil. Several years later, in order to provide more rooting space for the mature citrus trees, another soil chiselling trench was made beside the planting trench. Materials, including lime, fertilizer and organic manure, were mixed in both planting and chiselling trenches, rapidly increasing soil nutrients in the entire rooting depth and improving soil structure and other soil physical conditions. The yield observations showed that the citrus trees bore fruit one year earlier in the trench planted orchard than in the conventional orchard, and that the citrus yield increased more than three times in eight years after the citrus saplings were transplanted. 0 1997 Elsevier Science B.V. Keywords: Ultisols; Soil reclamation; Wrus production; Planting method; Amelioration of soil physical and chemical properties
1. Introduction Red soil derived from a variety of parent materials occur extensively in southern China occupying an area of 2.118 X lo6 km2 and accounting for 22% of the total land
’ Corresponding
author.
Tel.:
+ 86-01571-6091535;
0167.1987/97/$17.00 0 1997 Elsevier F’II SO167-1987(97)00024-X
fax:
+ 86-0571-6049815.
Science B.V. All rights reserved.
310
J. Lu et al. / Soil & Tillage Research
43 (1997)
309-318
area of the country. These soils often occur in gentle hilly areas, which stand up from the intensively cultivated soils of the alluvial plains, and are conveniently described as ‘hilly red soils’. Such soils would be classified as ultisols under the US system of soil taxonomy. The climate of southern China is characterized by abundant rainfall (annual rainfall of 1200-2500 mm) and high temperature (mean annual temperature range of 14-28°C) bioclimatic conditions that promote rapid plant growth and with the potential for producing enormous quantities of biomass (Zhao, 1992). However, the red hilly soils are characterized by acidity, low cation exchange capacity and lack of nutrients (Xu and Yao, 1992). Initial attempts to use the soils for arable crops after clearing of the natural forest led to serious erosion problems and it became clear that such usage was completely unsustainable. In addition to the inherent infertility of the soils, there are also problems with compactness and drought during later summer/autumn, thus limiting the exploitation of the red soils for agriculture (Gong and Shi, 1992). The challenge, therefore, is to find ways of utilizing the red soil for agricultural production on a sustainable basis. In the Quzhou region of Zhejiang province, located at 118-120”E and 2%29”N, there is a long history of citrus production. Previously, almost all of the citrus trees were planted in the river valley, but from the 1950s attempts were made to move citrus production to the hilly red soils (Lu and Yu, 1992) on which citrus trees do not survive without soil improvement. To counteract the excessive compactness, acidity and poor fertility of these soils, citrus production was first based on ‘small cavity planting’ (cavity of 50 cm in diameter) and later on ‘big cavity planting’ (cavity of 100 cm in diameter). These techniques involved mixing various fertilizing materials with soil from the cavities but were not widely adopted because of the very poor harvests. Since the late 1970s the techniques of trench planting and soil chiselling for citrus production have been developed in the region. The success of these techniques promoted the further development of citrus production and by 1990 the area of citrus orchard in the Quzhou region was more than 22,900 ha, which is 36 times that of 1970. The main reason for the success of the trench planting and soil chiselling techniques is that it creates enough ‘effective soil space’ for citrus root growth. It might also be anticipated that trench planting and soil chiselling would improve the physical and chemical properties of the soil. The objective of this paper is to quantify this improvement and to show its impact upon citrus production in terms of increased yields.
2. Materials
and methods
Contour strips were made along the contours of terraced land on slopes (< 15”) in hilly red soils. The trenches dug were 1.0 m wide and 0.8 m (or 1.0 m) deep. Lime (2.25-3.0 Mg ha-‘), calcium magnesium phosphate (1.5 Mg ha-‘), organic matter (more than 1.5 Mg ha-‘) and other materials (coal ash, household rubbish, sludge and so on) were mixed with the excavated soil, and then the mixed soil was refilled into the trench. The following spring, the citrus saplings were transplanted in the trench (Fig. 1). Because the surrounding soil was very compact and with poor fertility, almost all of
.I. Lu et al./Soil
Citrus Fig. 1. Citrus planting
citrus roots grow was very high. In width and 0.8 m were again mixed the soil chiselling ously high level.
& Tillage Research
planting
43 (1997)
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trench
Soil chiseling
trench and soil chiseling
trench in red soil region
trench
of China.
only in the trench space so that after 5-10 yr, the citrus root density order to extend the rooting space, another trench was made with 0.8 m depth beside the transplanting trench. Some lime and organic matter with the excavated soil, and then refilled. This practice showed that trench was very beneficial for maintaining citrus yields at a continu-
2.1. Soil sampling Soil from several citrus orchards (all from the same hill) reclaimed in different years was sampled at 3 to 5 sites each in a randomized design in Shilifen Farm, Quzhou city, Zhejiang province (Table l), where the trench planting and soil chiselling methods for citrus production in the red soils were first developed. The red soil (huanjinni) of the Chinese soil classification system, is equivalent to the ultisol order in the US taxonomy
Table 1 Some basic properties Sample number
Time since reclamation
unreclaimed 0 (just after reclamation) 1 Yr
2yr 4yr 8 yr 12 yr
of soil samples
&ken
at different
times after reclamation
Replicate (number of samples)
Particle
Sand (> 50 firn)
Silt (50-2
5 4
21.3 17.5
36.1 40.2
3 3 4 4 5
23.7 21.1 25.7 25.6 19.7
40.6 39.8 32.6 38.4 41.1
size distribution
(g 100 g-’ )
wrn)
pH (Hz01
O.M. (8 1OOg~‘)
42.6 42.3
4.9 5.1
0.23 0.33
36.1 39.1 41.7 36.0 39.2
5.3 5.2 5.3 6.3 6.3
0.43 0.61 0.83 1.10 0.89
Clay (<2
wm)
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system; its parent material is Quatemary red clay. Soil conditions for all orchards examined were very similar before soil reclamation. Because of high income potential, the fertilizer application was quite high and soil management was also very good after the red soil was reclaimed for citrus production. Therefore, in the top layer (O-20 cm) of the orchard soil profile, the nutrient concentration was very high with large amounts of organic manure residues. Soil samples were collected from three layers (O-20 cm, 20-60 cm, and 60-80 cm). The soil samples for the analysis of water-stable aggregate were collected from 20-60 cm depth so as to avoid fertilizer and manure effects. Because the action of soil &selling was very similar to that of the planting trench, soil samples were not collected from soil chiselling trench. The effects of soil chiselling on citrus production are shown directly in the observation of plant growth and citrus yields. 2.2. Measurements
of soil properties
The determination of soil properties (with two replicates each) included agrochemical properties (pH, organic matter, total N, P and K, available N, P and K, and CEC), mechanical properties (bulk density, crushing strength and three phase ratios), soil water characteristic and soil structure. Soil water-stable aggregate content was determined by a wet sieving method. Before determination, soil samples were treated by three methods with three replications each: (1) soaking with oxidant (6% H,O, solution, for 24 h), (2) soaking with a reducing-complexation reagent (C-D agent, a mixed solution of equal volumes of 0.1 mol/l citric acid and 0.1 mol/l sodium dithionite, for one week), and (3) soaking with a control. Agents (1) and (2) were used to destroy the soil structure cemented by soil organic matter and by Fe-film or Al-film, respectively (Lu et al., 1979). 2.3. Plant growth and citrus yield observations The citrus yields under the planting methods of small cavity, trench planting, and trench planting plus chiselling were recorded for different years after planting. The citrus variety and planting density was the same for all the three planting methods. Citrus variety was Satsuma, and the planting density was 5 X 4 m. The &selling trench was made in the sixth year after transplanting citrus saplings. Root system observations were made in three soil profiles just below the citrus tree for both small cavity and trench planted orchards. Shoot measurements and yield were expressed as the average of ten trees. The management for all citrus production was similar to that used conventionally at the local level. 3. Results and discussion 3.1. Comparison soil
of soil agrochemical properties
between unreclaimed soil and ripened
Due to erosion, the nutrient contents in the unreclaimed hilly red soil were very low. After it was reclaimed for citrus orchard, soil management was kept at a quite high
No. I’
0.51) 0.23 0.31
’
1.34’ 0.89* 1.01’
* * *
No. 7h
of the sod agrochemlcal
O.M. (g 100 g-1)
properties
0.044 0.034 0.026
No. ,
No. 7
between
0.070 * * 0.048 * 0.038 *
Total N (g 100 g-11 No. 1 0.0271 0.0052 0.0048
0.0301”s 0.0188 * * 0.0118 * *
No. 7
soil and ripened
Total P (g 100 g-1)
unreclaimed
aSoil sample no. 1. unreclaimed soil. as shown in Table 1. %oil sample no. 7. ripened soil (12 years after citrus trench plantmg, shown in Table Asterisk indicare significance by t-test at: ‘P < 0.05: * *P < 0.01; * * *P < 0.001. “‘Not significant.
O-20 20-60 60-80
(cm)
Soil depth
Table 2 Comparison
1).
47.0 24.6 21.5
No. I
Available (mg kg-‘)
soil (soil
68.0 * 45.0 * * 35.0 ’
No. 7
N
sample no. 7)
2.25 0.98 n.d.
No. I
Available (wkg-I)
7.76” * 5.05 I * 3.88
No. 7
P
43.33 22.83 20.00
No. 1
Available hg kg-‘)
34.79”s 43.79 * 17.91”s
No. 7
K
4.9 4.8 4.7
No. 1
PH (HzO) No. 7 6.3 ’ 7.6’ * 7.8 * *
9.5 7.3 7.0
No. 1
CEC (cmol kg-
14.9 * 10.6”” 5.9”s
No. 7
‘1
2 2 z 2
B 2 s
5
5
b 3 z
c w g
a
5 F 2
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level. Besides the fertilizer mixed in the trench soil, the application rates of nitrogen, phosphorus, and potassium were 350 (N), 109.2 (P), and 250 (K) kg ha-’ per year, respectively. Therefore, the nutrition conditions were rapidly improved in the entire rooting space (Table 2). In the ripening process of the orchard soil, organic material mixed in trench soil played a very important role. Soil survey of citrus orchards in the region showed that available nitrogen content was closely related to the soil organic matter content, with the relation between the available nitrogen (Y, mg kg-‘) and organic matter (X, g 100 g-‘) being described by the regression equation Y = 5.98 + 53.05X (68 observations, r = 0.6368 * * >. On the other hand, phosphate deficiency is one of the major factors limiting plant production in the acid red soil. The application of lime in trench planting process not only increased soil pH, but also promoted soil phosphorus mobilization, and increased its availability. As shown in Table 2, the total P (P,O,) of ripened soil (soil no. 7) increased by 1.1 and 3.6 times at O-20 and 20-60 cm, while the available P (P,O,) increased by 3.4 and 5.1 times, respectively. Thus soil phosphorus mobilization was closely related to soil pH. 3.2. Improvement of soil structure The improvement of soil physical properties is very important for citrus production in the red soils, because plant rooting is strongly limited by their compacted nature. Both soil texture and soil structure affect almost all soil physical properties. Soil texture is quite stable. Therefore, improving soil structure is one of most important tasks for citrus production in the red soil (Lu and Hu, 1991). The results of soil structure analysis showed that the quantity of water-stable aggregates (> 0.25 mm in diameter) changed greatly after the soil reclamation by trench planting. As shown in Fig. 2, the water-stable aggregate content of the unreclaimed soil was always the greatest. One year after soil
0’
Unreel.
I 0
I
2
/
4
I
6
Time after reclamation
Fig. 2. Change
of water-stable
aggregate
content
8
10
12
(Y’)
in red soil after different
reclaimed
years.
J. Lu et d/Soil
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reclamation, the soil water-stable aggregate content was low, only 24% of that for unreclaimed soil. Thereafter, the water-stable aggregate content increased again as time progressed, and maintained a relatively stable level after four years. Although the unreclaimed re’d soil has a very high water-stable aggregate content, it is very compact in the naturally wet subsoil layer. Therefore, this water-stable structure is not very meaningful for plant growth. The soil structure features of ripened soil are very different from those of unreclaimed soil. After treatment by oxidant and C-D reagents, the water-stable aggregate content of the unreclaimed soil was quite different from that of the ripened soil. The structure of the ripened soil was destroyed by oxidant much more than in the case of unreclaimed soil, but it was affected to a lesser extent than the unreclaimed soil when treated with the C-D reagent (Table 3). These results imply that the organic cementing material of soil structure might be more important for ripened soil, and Fe and Al might be more important for the structure of unreclaimed red soil. The extracted Fe and Al in the treatment solution of C-D reagent for the unreclaimed soil sample were 1138 and 1301 mg kg-‘, but were only 540 and 178 mg kg-’ for ripened soil. These results further substantiate the above suggestion. The evolution of water-stable structure indicates that the structure of red soil was improved during the reclamation and ripening process by replacement of some material that was cementing soil structure. In its natural state the structure of the red soil is mainly cemented by Fe and Al films. Exploitation by trench planting for citrus production destroys the soil structure by mechanical disturbance and through introducTable 3 Effect of oxidant and C-D reagent on water-stable (soil samples were taken from 20-60 cm depth) Soil samples
Aggregate diameter hd
Unreclaimed soil (soil sample no. 1)
Ripened soil (soil sample no. 7)
Comparison LSD,.,, LS”o.o,
between
>5 5-2 2-l l-0.5 0.5-0.25 Total ( > 0.25) >5 5-2 2-l l-0.5 0.5-0.25 Total ( > 0.25) total values
aggregate
Water-stable (g 100 g-‘)
aggregate
CHECK
Oxidant treatment
24.4 8.7 3.5 11.2 14.2
0 1.1 1.9 18.4 24.6
62.0 4.4 4.9 5.3 18.7 25.4
content
for the unreclaimed
content
and ripened
LSD,.,,
LSD,.,,
0.7 3.3 0.9 3.3 2.8
3.3 2.6 2.0 2.9 3.5
4.6 3.6 2.8 4.1 4.9
46.0 2.7 0.6 0.7 3.1 12.6
11.0 0.8 5.1 1.1 4.8 4.7
10.7 1.5 1.7 1.3 3.8 3.1
14.9 2.1 2.4 1.8 5.5 4.4
58.7
19.7
16.5
6.3
8.9
15.2 ‘22 1
7.1 10.4
3.2 4.6
C-D reagent treatment
red soils
316 Table 4 Comparison orchard Soil depth cm
O-20 20-60 60-80
J. Lu et al./Soil
of physical
properties
& Tillage Research
for unreclaimed
(soil
43 (1997)
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no. 1) and ripened
(soil no. 7) red soil in citrus
Crushing strength (N cmm3)
Bulk density (g mm31
Three phase ratio”
O.M.
Soil no. 1
Soil no. 7
Soil no. 1
Soil no. 7
Soil no. 1
Soil no. 7
Soil no. 1
49.9 16.7
30.6* * 26.5 = * *
1.26
1.11’
53:38:9
48:39:13
0.59
1.34*
* *
57~3617 57136~7
51:36:13 54:38:8
0.89*
* *
41.5=
1.22* 1.37""
0.23
60.1
1.34 1.32
0.31
1.01* * *
*
“Volume ratio of solid:liquid:air; measured at field capacity. Asterisk indicate significance by f-test at: *P < 0.05; * *P < 0.01; “SNot significant.
(g 100 g- ‘> Soil no. 7
* * * P < 0.001.
tion of organic matter mixed in trench soil. Then, as the degree of soil ripening increases organic material appears to replace iron and aluminum oxide films as the material that is cementing the soil structure. 3.3. Soil mechanical properties
and soil water retention capacity
The evolution of soil structure should cause a series of changes in other soil physical properties. As shown in Table 4, the crushing strengths of unreclaimed soil in topsoil and subsoil layers (O-20 and 20-60 cm) were higher than those of ripened soil 63% and 190%, respectively. The 20-60 cm depth is the layer of highest rooting density for citrus trees. The improvement of soil structure caused changes in both soil porosity and pore size distribution, and the analysis of three phase ratios showed that the transmission porosity of ripened red soil increased in all three soil layers (Table 4). Fig. 3 shows the soil water release characteristic curves at low suctions (O-80 kPa) for soil sample nos. 1, 3, and 7. The water release characteristics at low soil suction are
70 G Z B
60 50
+Soil
No.1
+Soil
No.3
tSoi1
No.7
I 0
20
40 Soil
suction
60
80
(kPa)
Fig. 3. Soil water characteristic curves for unreclaimed soil (soil no.11 and citrus orchard soils after trench planting for one year (soil no. 3) and for 12 years (soil no. 7). Vertical bars indicate LSD (P < 0.05).
J. Lu et al. /,Soil Table 5 Comparison Planting
of plant growth
method
and citrus yields
Root (cm) Deepest
under different
planting
methods
Shoot (cm) Concenltrateda
317
& Tillage Resear-ch 43 (19971 309-318
Crownb
Height
Main trunk diameter
in hilly
red soil
Yield
(Mg ha- ’ )
3
4
6
8
Small cavity Trench Trench+ chiseling”
110
20-50
175x171
175
14.4
0
3.7
12.4
12.8
132
30-80
277X267
8.3
-
292X269 -
26.5 -
=Qm fWm
30-80 -
23.8 24.6
2.9
-
227 286
-
-
3.0 4.9
7.8 13.0
43.4 51.0 9.4
14 20
aRooting concentrated layer. bCrown projection with cross diameter. “Chiselling trench was made in the sixth year after citrus sapling
5.1 1.4
-
2.3 3.7
15.5
transplant.
mainly dependent on soil structure. Fig. 3 shows that the saturation water content was greatest one year after trench planting, but that it decreased faster with increasing soil suction than in samples taken 12 years after trench planting. Both the water retention capacity and the saturated water content were very low for the unreclaimed red soil (soil no. 1). 3.4. Plant growth
and citrus yields
Trench planting is very beneficial for citrus production. Tree growth features were observed in the eighth year after citrus sapling transplanting. For the trench planted orchard, both the root system and shoots were better than those for the small cavity planted orchard. In the trench planted orchard, some fruit was harvested in the third year after transplanting, while it was one year later in the small cavity planted orchard (Table 5). The yields in the trench pla.nted orchard were much higher than those of the small cavity planted orchard (Table 5). Six years after citrus sapling transplanting, the yield continued to increase in the trench planted orchard, but it increased little in the small cavity planted orchard and the differences in yields between the two orchards become greater with time. The soil &selling trench method further extended the ‘effective rooting space’, to improve both the plant growth and yield after two years. 4. Conclusions Trench planting is a successful alternative method to conventional cavity planting for citrus production in hilly red soils. The materials mixed in the trench soil played very important roles in improving the conditions of the entire soil profile for citrus rooting space. Both total and available nitrogen contents increased rapidly and the application of lime increased the pH value of the soil, and promoted soil phosphorus mobilization. Under trench planting conditions, the structure of the red soil in terms of content of water-stable aggregates was significantly modified, as organic material replaced iron and aluminum oxide films as cementing material. This modification considerably affected many other soil physical properties. The soil crushing strengths for ripened orchard soil
318
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43 (1997)
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were only 61% and 34% of those for unreclaimed soil at O-20 and 20-60 cm soil depth, respectively, and there were improvements in soil porosity and pore size distribution, as well as increased soil water retention and supply capacities. Unlike conventional methods, trench planting and soil chiselling gave citrus more ‘effective rooting space’. This is beneficial to citrus growth as shown by the fact that citrus fruits could be harvested one year earlier and by the increased citrus fruit yields. These were 121%, 113%, and 239% greater than those from conventional orchards, 4, 6 and 8 yr after transplanting, respectively.
Acknowledgements This work was conducted with financial assistance from the European Economic Community Program (EECP). We also thank the Shilifen Agricultural Research Institute for its help in the field observations.
References Gong, Z., Shi, X., 1992. Rational soil utilization and soil degradation control in tropical China. In: Gong, Z. (Ed.), Proc. Int. Symposium on Management and Development of Red Soils in Asia and Pacific Region. Science Press, Beijing, New York, pp. 8-12. Lu, J., Lou, G., He, Z., Wu, Z., 1979. Stability of the structure of red earth and its significance in soil classification. Acta Pedol. Sin. 23, 212-218, (in Chinese, with English abstract). Lu, J., Hu, .I., 1991. Evolution of soil structure in the process of mellowing of red soil on low rolling hills. Chin. J. Soil Sci. 22, 45-48, (in Chinese). Lu, J., Yu, J., 1992. Studies on soil limitations and it’s amelioration in a citrus orchard of red earth on rolling hills. In: Lin, B. (Ed.), Modern Forest Management and Forest Soil Potential. International Academic Publishers, Beijing, pp. 24-29. Xu, X., Yao, X., 1992. Studies on physical properties of red soil in hilly region of central Jiangxi. In: Gong, Z. (Ed.), Proceedings of International Symposium on Management and Development of Red Soils in Asia and Pacific Region. Science Press, Beijing, New York, pp. 8-12. Zhao, Q., 1992. Ecological environment and integrated exploitation of the red soil hilly region of China. In: Gong, Z. (Ed.), Proceedings of International Symposium on Management and Development of Red Soils in Asia and Pacific Region. Science Press, Beijing, New York, pp. l-7.
Soil & TillaLge Research 43 (1997) 309-318
ELSEVIER
Effects of trench planting and soil chiselling on soil properties and citrus production in hilly ultisols of China Jun Lu a,*, M.J. Wilson b, Jinyan Yu a a Department
of Soil Science and Agrochemistry. Zhejiang Agricultural b Diuision of Soils, Macauluy Land Use Research Institute,
University, Hangzhou Aberdeen AB15 8QH,
310029, UK
China
Accepted 1 May 1997
Abstract Trench planting and soil chiselling are special techniques of soil utilization and reclamation for citrus production in the hilly red soil region of China. Serious erosion, acidity, compactness, low fertility, and seasonal drought are major problems in this region. These problems in the red soil (i.e., ultisol in US taxonomy system) limit plant production, especially that of deeply rooting plants. Trench planting was aimed at improving the entire rooting space for the citrus tree growth before the citrus saplings are transplanted to the red soil. Several years later, in order to provide more rooting space for the mature citrus trees, another soil chiselling trench was made beside the planting trench. Materials, including lime, fertilizer and organic manure, were mixed in both planting and chiselling trenches, rapidly increasing soil nutrients in the entire rooting depth and improving soil structure and other soil physical conditions. The yield observations showed that the citrus trees bore fruit one year earlier in the trench planted orchard than in the conventional orchard, and that the citrus yield increased more than three times in eight years after the citrus saplings were transplanted. 0 1997 Elsevier Science B.V. Keywords: Ultisols; Soil reclamation; Wrus production; Planting method; Amelioration of soil physical and chemical properties
1. Introduction Red soil derived from a variety of parent materials occur extensively in southern China occupying an area of 2.118 X lo6 km2 and accounting for 22% of the total land
’ Corresponding
author.
Tel.:
+ 86-01571-6091535;
0167.1987/97/$17.00 0 1997 Elsevier F’II SO167-1987(97)00024-X
fax:
+ 86-0571-6049815.
Science B.V. All rights reserved.
310
J. Lu et al. / Soil & Tillage Research
43 (1997)
309-318
area of the country. These soils often occur in gentle hilly areas, which stand up from the intensively cultivated soils of the alluvial plains, and are conveniently described as ‘hilly red soils’. Such soils would be classified as ultisols under the US system of soil taxonomy. The climate of southern China is characterized by abundant rainfall (annual rainfall of 1200-2500 mm) and high temperature (mean annual temperature range of 14-28°C) bioclimatic conditions that promote rapid plant growth and with the potential for producing enormous quantities of biomass (Zhao, 1992). However, the red hilly soils are characterized by acidity, low cation exchange capacity and lack of nutrients (Xu and Yao, 1992). Initial attempts to use the soils for arable crops after clearing of the natural forest led to serious erosion problems and it became clear that such usage was completely unsustainable. In addition to the inherent infertility of the soils, there are also problems with compactness and drought during later summer/autumn, thus limiting the exploitation of the red soils for agriculture (Gong and Shi, 1992). The challenge, therefore, is to find ways of utilizing the red soil for agricultural production on a sustainable basis. In the Quzhou region of Zhejiang province, located at 118-120”E and 2%29”N, there is a long history of citrus production. Previously, almost all of the citrus trees were planted in the river valley, but from the 1950s attempts were made to move citrus production to the hilly red soils (Lu and Yu, 1992) on which citrus trees do not survive without soil improvement. To counteract the excessive compactness, acidity and poor fertility of these soils, citrus production was first based on ‘small cavity planting’ (cavity of 50 cm in diameter) and later on ‘big cavity planting’ (cavity of 100 cm in diameter). These techniques involved mixing various fertilizing materials with soil from the cavities but were not widely adopted because of the very poor harvests. Since the late 1970s the techniques of trench planting and soil chiselling for citrus production have been developed in the region. The success of these techniques promoted the further development of citrus production and by 1990 the area of citrus orchard in the Quzhou region was more than 22,900 ha, which is 36 times that of 1970. The main reason for the success of the trench planting and soil chiselling techniques is that it creates enough ‘effective soil space’ for citrus root growth. It might also be anticipated that trench planting and soil chiselling would improve the physical and chemical properties of the soil. The objective of this paper is to quantify this improvement and to show its impact upon citrus production in terms of increased yields.
2. Materials
and methods
Contour strips were made along the contours of terraced land on slopes (< 15”) in hilly red soils. The trenches dug were 1.0 m wide and 0.8 m (or 1.0 m) deep. Lime (2.25-3.0 Mg ha-‘), calcium magnesium phosphate (1.5 Mg ha-‘), organic matter (more than 1.5 Mg ha-‘) and other materials (coal ash, household rubbish, sludge and so on) were mixed with the excavated soil, and then the mixed soil was refilled into the trench. The following spring, the citrus saplings were transplanted in the trench (Fig. 1). Because the surrounding soil was very compact and with poor fertility, almost all of
.I. Lu et al./Soil
Citrus Fig. 1. Citrus planting
citrus roots grow was very high. In width and 0.8 m were again mixed the soil chiselling ously high level.
& Tillage Research
planting
43 (1997)
311
309-318
trench
Soil chiseling
trench and soil chiseling
trench in red soil region
trench
of China.
only in the trench space so that after 5-10 yr, the citrus root density order to extend the rooting space, another trench was made with 0.8 m depth beside the transplanting trench. Some lime and organic matter with the excavated soil, and then refilled. This practice showed that trench was very beneficial for maintaining citrus yields at a continu-
2.1. Soil sampling Soil from several citrus orchards (all from the same hill) reclaimed in different years was sampled at 3 to 5 sites each in a randomized design in Shilifen Farm, Quzhou city, Zhejiang province (Table l), where the trench planting and soil chiselling methods for citrus production in the red soils were first developed. The red soil (huanjinni) of the Chinese soil classification system, is equivalent to the ultisol order in the US taxonomy
Table 1 Some basic properties Sample number
Time since reclamation
unreclaimed 0 (just after reclamation) 1 Yr
2yr 4yr 8 yr 12 yr
of soil samples
&ken
at different
times after reclamation
Replicate (number of samples)
Particle
Sand (> 50 firn)
Silt (50-2
5 4
21.3 17.5
36.1 40.2
3 3 4 4 5
23.7 21.1 25.7 25.6 19.7
40.6 39.8 32.6 38.4 41.1
size distribution
(g 100 g-’ )
wrn)
pH (Hz01
O.M. (8 1OOg~‘)
42.6 42.3
4.9 5.1
0.23 0.33
36.1 39.1 41.7 36.0 39.2
5.3 5.2 5.3 6.3 6.3
0.43 0.61 0.83 1.10 0.89
Clay (<2
wm)
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system; its parent material is Quatemary red clay. Soil conditions for all orchards examined were very similar before soil reclamation. Because of high income potential, the fertilizer application was quite high and soil management was also very good after the red soil was reclaimed for citrus production. Therefore, in the top layer (O-20 cm) of the orchard soil profile, the nutrient concentration was very high with large amounts of organic manure residues. Soil samples were collected from three layers (O-20 cm, 20-60 cm, and 60-80 cm). The soil samples for the analysis of water-stable aggregate were collected from 20-60 cm depth so as to avoid fertilizer and manure effects. Because the action of soil &selling was very similar to that of the planting trench, soil samples were not collected from soil chiselling trench. The effects of soil chiselling on citrus production are shown directly in the observation of plant growth and citrus yields. 2.2. Measurements
of soil properties
The determination of soil properties (with two replicates each) included agrochemical properties (pH, organic matter, total N, P and K, available N, P and K, and CEC), mechanical properties (bulk density, crushing strength and three phase ratios), soil water characteristic and soil structure. Soil water-stable aggregate content was determined by a wet sieving method. Before determination, soil samples were treated by three methods with three replications each: (1) soaking with oxidant (6% H,O, solution, for 24 h), (2) soaking with a reducing-complexation reagent (C-D agent, a mixed solution of equal volumes of 0.1 mol/l citric acid and 0.1 mol/l sodium dithionite, for one week), and (3) soaking with a control. Agents (1) and (2) were used to destroy the soil structure cemented by soil organic matter and by Fe-film or Al-film, respectively (Lu et al., 1979). 2.3. Plant growth and citrus yield observations The citrus yields under the planting methods of small cavity, trench planting, and trench planting plus chiselling were recorded for different years after planting. The citrus variety and planting density was the same for all the three planting methods. Citrus variety was Satsuma, and the planting density was 5 X 4 m. The &selling trench was made in the sixth year after transplanting citrus saplings. Root system observations were made in three soil profiles just below the citrus tree for both small cavity and trench planted orchards. Shoot measurements and yield were expressed as the average of ten trees. The management for all citrus production was similar to that used conventionally at the local level. 3. Results and discussion 3.1. Comparison soil
of soil agrochemical properties
between unreclaimed soil and ripened
Due to erosion, the nutrient contents in the unreclaimed hilly red soil were very low. After it was reclaimed for citrus orchard, soil management was kept at a quite high
No. I’
0.51) 0.23 0.31
’
1.34’ 0.89* 1.01’
* * *
No. 7h
of the sod agrochemlcal
O.M. (g 100 g-1)
properties
0.044 0.034 0.026
No. ,
No. 7
between
0.070 * * 0.048 * 0.038 *
Total N (g 100 g-11 No. 1 0.0271 0.0052 0.0048
0.0301”s 0.0188 * * 0.0118 * *
No. 7
soil and ripened
Total P (g 100 g-1)
unreclaimed
aSoil sample no. 1. unreclaimed soil. as shown in Table 1. %oil sample no. 7. ripened soil (12 years after citrus trench plantmg, shown in Table Asterisk indicare significance by t-test at: ‘P < 0.05: * *P < 0.01; * * *P < 0.001. “‘Not significant.
O-20 20-60 60-80
(cm)
Soil depth
Table 2 Comparison
1).
47.0 24.6 21.5
No. I
Available (mg kg-‘)
soil (soil
68.0 * 45.0 * * 35.0 ’
No. 7
N
sample no. 7)
2.25 0.98 n.d.
No. I
Available (wkg-I)
7.76” * 5.05 I * 3.88
No. 7
P
43.33 22.83 20.00
No. 1
Available hg kg-‘)
34.79”s 43.79 * 17.91”s
No. 7
K
4.9 4.8 4.7
No. 1
PH (HzO) No. 7 6.3 ’ 7.6’ * 7.8 * *
9.5 7.3 7.0
No. 1
CEC (cmol kg-
14.9 * 10.6”” 5.9”s
No. 7
‘1
2 2 z 2
B 2 s
5
5
b 3 z
c w g
a
5 F 2
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level. Besides the fertilizer mixed in the trench soil, the application rates of nitrogen, phosphorus, and potassium were 350 (N), 109.2 (P), and 250 (K) kg ha-’ per year, respectively. Therefore, the nutrition conditions were rapidly improved in the entire rooting space (Table 2). In the ripening process of the orchard soil, organic material mixed in trench soil played a very important role. Soil survey of citrus orchards in the region showed that available nitrogen content was closely related to the soil organic matter content, with the relation between the available nitrogen (Y, mg kg-‘) and organic matter (X, g 100 g-‘) being described by the regression equation Y = 5.98 + 53.05X (68 observations, r = 0.6368 * * >. On the other hand, phosphate deficiency is one of the major factors limiting plant production in the acid red soil. The application of lime in trench planting process not only increased soil pH, but also promoted soil phosphorus mobilization, and increased its availability. As shown in Table 2, the total P (P,O,) of ripened soil (soil no. 7) increased by 1.1 and 3.6 times at O-20 and 20-60 cm, while the available P (P,O,) increased by 3.4 and 5.1 times, respectively. Thus soil phosphorus mobilization was closely related to soil pH. 3.2. Improvement of soil structure The improvement of soil physical properties is very important for citrus production in the red soils, because plant rooting is strongly limited by their compacted nature. Both soil texture and soil structure affect almost all soil physical properties. Soil texture is quite stable. Therefore, improving soil structure is one of most important tasks for citrus production in the red soil (Lu and Hu, 1991). The results of soil structure analysis showed that the quantity of water-stable aggregates (> 0.25 mm in diameter) changed greatly after the soil reclamation by trench planting. As shown in Fig. 2, the water-stable aggregate content of the unreclaimed soil was always the greatest. One year after soil
0’
Unreel.
I 0
I
2
/
4
I
6
Time after reclamation
Fig. 2. Change
of water-stable
aggregate
content
8
10
12
(Y’)
in red soil after different
reclaimed
years.
J. Lu et d/Soil
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reclamation, the soil water-stable aggregate content was low, only 24% of that for unreclaimed soil. Thereafter, the water-stable aggregate content increased again as time progressed, and maintained a relatively stable level after four years. Although the unreclaimed re’d soil has a very high water-stable aggregate content, it is very compact in the naturally wet subsoil layer. Therefore, this water-stable structure is not very meaningful for plant growth. The soil structure features of ripened soil are very different from those of unreclaimed soil. After treatment by oxidant and C-D reagents, the water-stable aggregate content of the unreclaimed soil was quite different from that of the ripened soil. The structure of the ripened soil was destroyed by oxidant much more than in the case of unreclaimed soil, but it was affected to a lesser extent than the unreclaimed soil when treated with the C-D reagent (Table 3). These results imply that the organic cementing material of soil structure might be more important for ripened soil, and Fe and Al might be more important for the structure of unreclaimed red soil. The extracted Fe and Al in the treatment solution of C-D reagent for the unreclaimed soil sample were 1138 and 1301 mg kg-‘, but were only 540 and 178 mg kg-’ for ripened soil. These results further substantiate the above suggestion. The evolution of water-stable structure indicates that the structure of red soil was improved during the reclamation and ripening process by replacement of some material that was cementing soil structure. In its natural state the structure of the red soil is mainly cemented by Fe and Al films. Exploitation by trench planting for citrus production destroys the soil structure by mechanical disturbance and through introducTable 3 Effect of oxidant and C-D reagent on water-stable (soil samples were taken from 20-60 cm depth) Soil samples
Aggregate diameter hd
Unreclaimed soil (soil sample no. 1)
Ripened soil (soil sample no. 7)
Comparison LSD,.,, LS”o.o,
between
>5 5-2 2-l l-0.5 0.5-0.25 Total ( > 0.25) >5 5-2 2-l l-0.5 0.5-0.25 Total ( > 0.25) total values
aggregate
Water-stable (g 100 g-‘)
aggregate
CHECK
Oxidant treatment
24.4 8.7 3.5 11.2 14.2
0 1.1 1.9 18.4 24.6
62.0 4.4 4.9 5.3 18.7 25.4
content
for the unreclaimed
content
and ripened
LSD,.,,
LSD,.,,
0.7 3.3 0.9 3.3 2.8
3.3 2.6 2.0 2.9 3.5
4.6 3.6 2.8 4.1 4.9
46.0 2.7 0.6 0.7 3.1 12.6
11.0 0.8 5.1 1.1 4.8 4.7
10.7 1.5 1.7 1.3 3.8 3.1
14.9 2.1 2.4 1.8 5.5 4.4
58.7
19.7
16.5
6.3
8.9
15.2 ‘22 1
7.1 10.4
3.2 4.6
C-D reagent treatment
red soils
316 Table 4 Comparison orchard Soil depth cm
O-20 20-60 60-80
J. Lu et al./Soil
of physical
properties
& Tillage Research
for unreclaimed
(soil
43 (1997)
309-318
no. 1) and ripened
(soil no. 7) red soil in citrus
Crushing strength (N cmm3)
Bulk density (g mm31
Three phase ratio”
O.M.
Soil no. 1
Soil no. 7
Soil no. 1
Soil no. 7
Soil no. 1
Soil no. 7
Soil no. 1
49.9 16.7
30.6* * 26.5 = * *
1.26
1.11’
53:38:9
48:39:13
0.59
1.34*
* *
57~3617 57136~7
51:36:13 54:38:8
0.89*
* *
41.5=
1.22* 1.37""
0.23
60.1
1.34 1.32
0.31
1.01* * *
*
“Volume ratio of solid:liquid:air; measured at field capacity. Asterisk indicate significance by f-test at: *P < 0.05; * *P < 0.01; “SNot significant.
(g 100 g- ‘> Soil no. 7
* * * P < 0.001.
tion of organic matter mixed in trench soil. Then, as the degree of soil ripening increases organic material appears to replace iron and aluminum oxide films as the material that is cementing the soil structure. 3.3. Soil mechanical properties
and soil water retention capacity
The evolution of soil structure should cause a series of changes in other soil physical properties. As shown in Table 4, the crushing strengths of unreclaimed soil in topsoil and subsoil layers (O-20 and 20-60 cm) were higher than those of ripened soil 63% and 190%, respectively. The 20-60 cm depth is the layer of highest rooting density for citrus trees. The improvement of soil structure caused changes in both soil porosity and pore size distribution, and the analysis of three phase ratios showed that the transmission porosity of ripened red soil increased in all three soil layers (Table 4). Fig. 3 shows the soil water release characteristic curves at low suctions (O-80 kPa) for soil sample nos. 1, 3, and 7. The water release characteristics at low soil suction are
70 G Z B
60 50
+Soil
No.1
+Soil
No.3
tSoi1
No.7
I 0
20
40 Soil
suction
60
80
(kPa)
Fig. 3. Soil water characteristic curves for unreclaimed soil (soil no.11 and citrus orchard soils after trench planting for one year (soil no. 3) and for 12 years (soil no. 7). Vertical bars indicate LSD (P < 0.05).
J. Lu et al. /,Soil Table 5 Comparison Planting
of plant growth
method
and citrus yields
Root (cm) Deepest
under different
planting
methods
Shoot (cm) Concenltrateda
317
& Tillage Resear-ch 43 (19971 309-318
Crownb
Height
Main trunk diameter
in hilly
red soil
Yield
(Mg ha- ’ )
3
4
6
8
Small cavity Trench Trench+ chiseling”
110
20-50
175x171
175
14.4
0
3.7
12.4
12.8
132
30-80
277X267
8.3
-
292X269 -
26.5 -
=Qm fWm
30-80 -
23.8 24.6
2.9
-
227 286
-
-
3.0 4.9
7.8 13.0
43.4 51.0 9.4
14 20
aRooting concentrated layer. bCrown projection with cross diameter. “Chiselling trench was made in the sixth year after citrus sapling
5.1 1.4
-
2.3 3.7
15.5
transplant.
mainly dependent on soil structure. Fig. 3 shows that the saturation water content was greatest one year after trench planting, but that it decreased faster with increasing soil suction than in samples taken 12 years after trench planting. Both the water retention capacity and the saturated water content were very low for the unreclaimed red soil (soil no. 1). 3.4. Plant growth
and citrus yields
Trench planting is very beneficial for citrus production. Tree growth features were observed in the eighth year after citrus sapling transplanting. For the trench planted orchard, both the root system and shoots were better than those for the small cavity planted orchard. In the trench planted orchard, some fruit was harvested in the third year after transplanting, while it was one year later in the small cavity planted orchard (Table 5). The yields in the trench pla.nted orchard were much higher than those of the small cavity planted orchard (Table 5). Six years after citrus sapling transplanting, the yield continued to increase in the trench planted orchard, but it increased little in the small cavity planted orchard and the differences in yields between the two orchards become greater with time. The soil &selling trench method further extended the ‘effective rooting space’, to improve both the plant growth and yield after two years. 4. Conclusions Trench planting is a successful alternative method to conventional cavity planting for citrus production in hilly red soils. The materials mixed in the trench soil played very important roles in improving the conditions of the entire soil profile for citrus rooting space. Both total and available nitrogen contents increased rapidly and the application of lime increased the pH value of the soil, and promoted soil phosphorus mobilization. Under trench planting conditions, the structure of the red soil in terms of content of water-stable aggregates was significantly modified, as organic material replaced iron and aluminum oxide films as cementing material. This modification considerably affected many other soil physical properties. The soil crushing strengths for ripened orchard soil
318
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were only 61% and 34% of those for unreclaimed soil at O-20 and 20-60 cm soil depth, respectively, and there were improvements in soil porosity and pore size distribution, as well as increased soil water retention and supply capacities. Unlike conventional methods, trench planting and soil chiselling gave citrus more ‘effective rooting space’. This is beneficial to citrus growth as shown by the fact that citrus fruits could be harvested one year earlier and by the increased citrus fruit yields. These were 121%, 113%, and 239% greater than those from conventional orchards, 4, 6 and 8 yr after transplanting, respectively.
Acknowledgements This work was conducted with financial assistance from the European Economic Community Program (EECP). We also thank the Shilifen Agricultural Research Institute for its help in the field observations.
References Gong, Z., Shi, X., 1992. Rational soil utilization and soil degradation control in tropical China. In: Gong, Z. (Ed.), Proc. Int. Symposium on Management and Development of Red Soils in Asia and Pacific Region. Science Press, Beijing, New York, pp. 8-12. Lu, J., Lou, G., He, Z., Wu, Z., 1979. Stability of the structure of red earth and its significance in soil classification. Acta Pedol. Sin. 23, 212-218, (in Chinese, with English abstract). Lu, J., Hu, .I., 1991. Evolution of soil structure in the process of mellowing of red soil on low rolling hills. Chin. J. Soil Sci. 22, 45-48, (in Chinese). Lu, J., Yu, J., 1992. Studies on soil limitations and it’s amelioration in a citrus orchard of red earth on rolling hills. In: Lin, B. (Ed.), Modern Forest Management and Forest Soil Potential. International Academic Publishers, Beijing, pp. 24-29. Xu, X., Yao, X., 1992. Studies on physical properties of red soil in hilly region of central Jiangxi. In: Gong, Z. (Ed.), Proceedings of International Symposium on Management and Development of Red Soils in Asia and Pacific Region. Science Press, Beijing, New York, pp. 8-12. Zhao, Q., 1992. Ecological environment and integrated exploitation of the red soil hilly region of China. In: Gong, Z. (Ed.), Proceedings of International Symposium on Management and Development of Red Soils in Asia and Pacific Region. Science Press, Beijing, New York, pp. l-7.