effect of land use on soil nutrients in the loess hilly area of the loess plateau, china

land degradation & development

Land Degrad. Develop. 17: 453–465 (2006)

Published online 3 August 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ldr.701

EFFECT OF LAND USE ON SOIL NUTRIENTS IN THELOESS HILLYAREA OF THE LOESS PLATEAU, CHINA

J. GONG, L. CHEN,* B. FU, Y. HUANG, Z. HUANG AND H. PENG

Key Lab of Systems Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences,PO Box 2871, Beijing 100085, China

Received 12 January 2005; Revised 18 February 2005; Accepted 24 May 2005

ABSTRACT

Understanding the effects of land use change on soil properties is important for soil quality improvement and sustainable landuse. In this study, six land use types including wasteland (WLD), cropland (CLD), abandoned land (ABD), artificial grassland(AGD), shrubland (SLD) and woodland (WOD) were selected to analyse the effects of land use types on soil nutrient in theAnjiapo catchment in the western part of the Loess Plateau in China. Significant differences were found in soil organic matter(SOM), total nitrogen (TN) and nitrate nitrogen (NON) (P< 0.01) between the six land use types. Our study also showed thatland use types have different effects on soil nutrient storage, and vegetation restoration may improve soil nutrients and soilquality. While crop plantation can significantly decrease soil fertility, the trend can be reversed by cropland abandonment andafforestation. It is recommended that more C input, alternative cultivation practices, vegetation restoration and education andtechniques training of local farmers could be used to improve soil conditions and to advance the sustainable land use and localdevelopment in the loess hilly area in the Loess Plateau of China. Copyright # 2005 John Wiley & Sons, Ltd.

key words: land use change; soil nutrients; vegetation restoration; Grain-for-Green Policy; Loess Plateau of China

INTRODUCTION

Changes in land use and land cover have important impacts on natural resources through the changes in soil and

water quality, biodiversity, and global climatic systems that they cause (Houghton, 1994; Chen et al., 2001). Land

use and management practices may affect the direction and amplitude of changes in the soil environment

(Wang and Gong, 1998; Wang et al., 2004). As the fundamental resource for nearly all land types, and the most

important component of sustainable development (Nambiar et al., 2001; Bouma, 2002), soil plays a major role in

the global change, especially in the global C cycle (Schimel, 1995; Lal, 2002; Saroa and Lal, 2003). Recently,

increasing attention has been paid to the impact of the global land use change impacts on soil nutrient,

biogeochemical cycles (Houghton et al., 2000; Priess et al., 2001). Therefore, it is important to analyse soil

quality (Karlen et al., 1997) and the direction of its change with time (Doran, 2002; Herrick, 2000), and to use

these as primary indicators of sustainable land use and management (Smith et al., 1994; Doran, 2002). Moreover,

an analysis on changes of soil properties due to the land use change can support decision and policy-making

processes at regional and national levels. These include soil physical, chemical and/or biological properties

(Nambiar et al., 2001; Arshad and Martin, 2002; Doran, 2002; Mulugeta et al., 2005). Their changes may be

assessed by measuring and comparing present values against the values at the commencement of the monitoring

Copyright # 2005 John Wiley & Sons, Ltd.

�Correspondence to: L. Chen, Key Lab of Systems Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences,PO Box 2871, Beijing 100085, China.E-mail: [email protected]

Contract/grant sponsor: National Natural Science Foundation of China; contract/grant number: 40321101.Contract/grant sponsor: National Advanced Project of the Tenth Five-year Plan of China; contract/grant number: 2001BA606A-03.

period (Arshad and Martin, 2002), historical data when available (Hartemink, 1998), and soil properties under

reference ecosystems (Feigl et al., 1995; Wang and Gong, 1998), or by using values measured at different time

intervals (Mulugeta et al., 2005).

The Loess Plateau in China is known for its serious soil erosion. Currently, the surface soil loss in most hilly

areas of the Loess Plateau reaches approximately 5000–10 000Mg km�2 y�1 (Jiang, 1997), which results in much

nutrient loss and land degradation. Because of this, the Loess Plateau has received much attention from the

Chinese Government as well as many international organizations. Many studies indicated that soil erosion on the

Loess Plateau is mainly caused by irrational land use and low vegetation coverage (Fu and Gulinck, 1994;

Jiang, 1997). The Chinese Government acknowledges the severity of this problem and actively implements

comprehensive erosion control through a variety of measures.

The Slope Land Conversion Program (SLCP), known colloquially as the ‘Grain-for-Green Policy’, is one of the

key programmes in the central government’s efforts at forest restoration. The programme, which was mainly a

response to the severe flooding in China in 1998, aims at replanting forest or grassland on agricultural lands with a

slope of over 25 degrees, improving watershed conditions, enhancing biodiversity, and conserving natural

resources (Ye et al., 2003). The ‘Grain-for-Green Policy’ was initiated in 1999 with the goal of converting about

15 million hectares of low-yield slope farmland into woodland/grassland and of afforesting another 17 million

hectares of barren mountains in the upper reaches of the Yangtze River and the middle and upper reaches of the

Yellow River. In 2000, the programme was expanded to 10 provinces that are located in western China. These

provinces, known for their backward economy and vulnerable environment, consist of Sichuan, Guizhou and

Yunnan, Chongqing Municipality, Tibet Autonomous Region in the southwest, and Shaanxi, Gansu, Qinghai, and

the Autonomous Regions of Ningxia and Xinjiang in the northwest. A total of 867 counties are located in these

provinces, which account for more than one-half of China’s total area. According to the programme, the severely

eroded farmland will be changed into woodland over a short period to control the soil and water loss, and to

improve the regional environment (Ye et al., 2003).

To compensate them for the economic loss, farmers will be given grain, cash and planting stock as subsidies and

incentives for turning cultivated land back into forest and grassland. These entitlements would continue for at least

eight years for ecological forests and five years for timber production forests and orchards to ensure that farmers

will not revert to agriculture in the areas designated for redeveloped forest and grassland. For every hectare of

forest or grassland redeveloped, farmers in the upper reaches of the Yangtze River will receive 2250 kg of grain

every year while farmers in the upper and middle reaches of the Yellow River will receive 1500 kg of grain every

year. Farmers will also receive seeds and planting stock with an estimated average value of 750 Yuan RMB

(1 Chinese, Yuan¼ 0.12 US Dollars) per hectare to afforest/plant grass on the slope farmland. The government

will also give farmers 300 Yuan RMB per year for every hectare of forest and grassland they redevelop, to help

cover medical and educational expenses (State Forestry Administration Bureau (SFAB), 2000). This policy has

received positive responses from most of the farmers. So far, more farmland has been converted to forests and

grasslands than expected (Xu and Cao, 2002). To minimize the income loss that farmers might suffer from forest

and grassland restoration, it is suggested that where natural conditions allow, fruit and other commercially

valuable trees be planted. While the government will provide seedlings, farmers will be responsible for taking care

of the restored forests and pastures and will retain all the profits from planting trees and grass on cultivated land

(Feng et al., in press).

The ‘Grain-for-Green Policy’ poses new questions for scientists and decision/policy makers. What is the impact

of the land use change on soil properties? Can vegetation restoration improve the soil quality? These and other

new questions may elicit fresh insights and approaches from us (Janzen, 2004). In this study, we selected six land

use types and studied the changes of soil nutrients under different land use types. Our goal was to better estimate

the nutrient storage in the soil with different land use types and, furthermore, to provide a scientific basis for the

sustainable land use types and ‘Grain-for-Green Policy’.

The objectives of this study were: (1) to understand the effects of land use types and vegetation restoration on

soil nutrients; and (2) to make suggestions for the ‘Grain-for-Green Policy’ and the sustainable land use for the

loess hilly area of the Loess Plateau.

454 J. GONG ET AL.

Copyright # 2005 John Wiley & Sons, Ltd. LAND DEGRADATION & DEVELOPMENT, 17: 453–465 (2006)

MATERIALS AND METHODS

Study Area

This study was carried out in Anjiapo catchment (35�330–35�350 N, 104�380–104�400 E), which is located at

Dingxi, Gansu province in the western part of the Loess Plateau of China (Figure 1). The catchment covers an area

of 3�84 km2 with an altitude from 1900m to 2250m above sea level. The study area is a part of the loess hilly area

with a semiarid continental climate. According to the record at Dingxi Meteorological Station, the mean annual

precipitation is 427mm (1951–1990). The maximum annual precipitation was 721�8mm and occurred in 1967 and

the minimum annual precipitation was 245�7mm and occurred in 1982. Around 56 per cent of the precipitation

occurs between July and September. Little runoff is observed during the dry season (winter) while a high runoff

tends to happen during the rainy season (summer). Monthly mean temperatures range from 34�3�C in July to

�27�1�C in January. The potential yearly evaporation is about 1445mm with the monthly average ranging from

20mm to 80mm in the winter and 150mm to 270mm in the summer. The soil in the study area was developed

from wind-accumulated loess with the clay content ranging from 33�1 to 42�1 per cent, which is weak resistance toerosion (Fu and Gulinck, 1994). The soil erosion rate is extremely high at about 8000–10 000Mg km�2 y�1. Native

vegetation is comprised of typical temperate steppe, including wheatgrass (Agropyron cristatum) and capillary

sagebrush (Artemisia capillaris), etc.

The study area belongs to the rain-fed dryland agricultural production zone. The cropland was the main land use

type in the area and covered 60�19 per cent of the whole catchment area. Most of the croplands were terrace

(95�93 per cent) and slope farmland was very small (only 4�07 per cent) in 2002 (Huang, 2004). The farming

practices were monoculture with crop harvesting only once a year due to the lack of heat and the low temperatures.

Major crops are spring wheat (Triticum aestivum L.), beans (Phaseolus vulgaris), potato (Solanum tuberosum L.),

millet (Panicum miliaceum), oriental sesame (Sesamum indicum L.).

Our experimental design was to compare six typical land use types: wasteland (WLD), woodland (WOD),

cropland (CLD), shrubland (SLD), artificial grassland (AGD) and abandoned cropland (ABD). The information on

afforestation and land use history were derived by interviewing the experimental station managers and local

Figure 1. Location of the study area.

EFFECT OF LAND USE ON SOIL NUTRIENTS 455


farmers. Wastelands, as a widespread land cover, existed in this study area for a long time before our study and

were dominated by wheatgrass (A. cristatum) and capillary sagebrush (A. calillaris). Croplands, a traditional land

use, were continuously tilled and planted with potato (Solanum tuberosum L.) or beans (Phaseolus vaulgaris) for

almost 25 years by farmers before our study. Alfalfa (Medicago sativa), as artificial grassland, was planted three

years ago. Trees including Chinese pine (Pinus tabulaeformis) and apricot (Prunus armeniaca), were planted as a

woodland 25 years ago. Shrubs such as peashrub (Caragana korshinskii), were planted in the shrubland, at the

same time as the trees. The abandoned land came into being two to three years later when cultivated plots were

disused and became dominated by self-restorative vegetation such as capillary sagebrush (A. capillaris).

Soil Sampling and Analysis

Soil samples were collected in April 2003 on the representative sites of each land use type with homogeneous

plant composition, geomorphologic, and hydrologic conditions. Within each site, soil samples from the layers at

0–20 cm and 20–40 cm were collected from five points by soil auger and mixed as one composite sample.

Collected soil samples were air-dried and transported to the Institute of Soil and Water Conservation of the

Chinese Academy of Sciences in Yangling, Shannxi Province for the determination of soil nutrients.

The following soil properties were determined. Soil organic matter (SOM) was determined by the K2CrO7

titration method, total nitrogen (TN) by the semi-micro Kjeldahl method, total phosphorus (TP) colorimetrically

after wet digestion with H2SO4þHClO4, available K (AK) and available phosphorus (AP) colorimetrically after

digestion with 3 per cent ammonium carbonate extraction, nitrate nitrogen (NON) and ammonia nitrogen (NHN)

by a micro-diffusion technique after potassium chloride extraction (Editorial Committee, 1996).

Statistical Analysis

One-way analysis of variance (ANOVA) was performed on each soil property of each soil layer to test whether the

changes in the soil properties investigated were statistically significant (P< 0.05). When necessary, data were log-

transformed prior to statistical analysis to meet the requirement of normal distribution of data. Mean values were

compared using least significant difference (LSD). All the data processing was conducted by SPSS program

(SPSS, 2001; Version 10.0).

RESULTS ANALYSIS

Effects of Different Land Use Types on Soil Properties

Changes in soil nutrients under different land use types are presented in Table I. Statistically significant differences

(P< 0.01) were found in SOM, TN and NON of both soil layers among the six land use types (Table I). Significant

differences (P< 0.01) were found in AP and AK in the topsoil layer (0–20 cm) among the six land use types (Table

I). As far as AP and AKof the soil layer (20–40 cm) were concerned, AP was different at P< 0.05, but there was no

significant difference in AK. As for TP and NHN, there was no marked difference in either soil layer among the six

land use types (Table I).

Changes of SOM Under Different Land Use Types

Different land use types had different effects on soil organic matter (Figure 2). SOM under different land use types

declined with the increase in soil depth. SLD had the largest SOM content in the both soil layers. There was no

significant difference in SOM between WLD and WOD. Although no significant difference remained in SOM

content among CLD, ABD and AGD; CLD is the smallest one.

Vegetation restoration, such as shrub, tree and grass plantation and cropland abandonment, increased the SOM

content. The increase rate varied among the different land–vegetation systems (Figure 2). Compared with CLD,

the SOM content of the soil layer (0–20 cm) of WLD, ABD, AGD, SLD and WOD increased by 77.63 per cent,

25.00 per cent, 22.37 per cent, 188.16 per cent and 47.37 per cent, respectively; and it increased by 41.10 per cent,

456 J. GONG ET AL.


12.33 per cent, 24.66 per cent, 165.75 per cent and 47.95 per cent, respectively, for WLD, ABD, AGD, SLD and

WOD in the 20–40 cm soil layer. These results indicate that the conversion of cultivated land to grassland, forest

and shrubland would improve the soil fertility. While crop production may significantly decrease SOM, and it

appears that the trend can be reversed with cropland abandonment and subsequent vegetation regeneration.

Changes of Soil N Under Different Land Use Types

Although soil N was accumulated mostly at the topsoil layer of 20 cm, the effects of different land use types on soil

N were different. Soil N under different land use types declined with soil depth increase (Figures 3, 4 and 5).

Figure 2. Changes of soil organic matter (SOM) under different land use types (error bars represent standard error). Different letters above barsrepresent statistically significant differences at P< 0.05 of the 0–20 cm and 20–40 cm soil layers, respectively. Note: WLD¼wasteland;

CLD¼ cropland; ABD¼ abandoned land; AGD¼ artificial grassland; SLD¼ shrubland; WOD¼woodland.

Table I. Change of soil nutrient of the samples under different land use types

Soil nutrient Soil depth (cm) WLD CLD ABD AGD SLD WOD ANOVA

SOM (%) 0–20 1.347 0.766 0.947 0.930 2.187 1.308 **20–40 1.031 0.736 0.825 0.908 1.944 1.082 **

TN (%) 0–20 0.083 0.057 0.062 0.065 0.141 0.084 **20–40 0.072 0.054 0.056 0.062 0.131 0.068 **

TP (%) 0–20 0.064 0.067 0.067 0.069 0.063 0.064 nsa

20–40 0.062 0.064 0.068 0.067 0.062 0.062 nsAP (mg kg�1) 0–20 7.614 12.374 7.743 6.096 3.734 2.605 **

20–40 4.331 6.658 4.908 7.528 2.423 1.740 *NON (mg kg�1) 0–20 12.768 9.589 5.765 7.394 21.656 9.125 **

20–40 7.848 10.214 5.007 6.616 17.986 7.932 **NHN (mg kg�1) 0–20 9.38 9.099 8.568 8.932 9.516 9.200 ns

20–40 8.820 8.054 9.207 7.608 9.358 7.807 nsAK (mg kg�1) 0–20 242.50 123.26 181.38 153.08 226.55 204.25 **

20–40 138.13 98.56 126.87 136.12 160.78 134.25 ns

*Significant at P< 0.05; **Significant at P< 0.01.aNot significant at P< 0.05; BD¼ soil bulk density; SOM¼ soil organic matter; TN¼ total nitrogen; TP¼ total phosphorous; AP¼ availablephosphorous; NON¼ nitrate nitrogen; NHN¼ ammonium nitrogen; AK¼ available potassium.WLD¼wasteland; CLD¼ cropland; ABD¼ abandoned land; AGD¼ artificial grassland; SLD¼ shrubland; WOD¼woodland.



As to TN (Figure 3), SLD had the highest soil TN content at the topsoil layers of 20 cm (0.141� 0.006 per cent,

P< 0.01). There was no significant difference between WLD and WOD in the top 20 cm soil layer. Although there

may be no significant difference in TN content among CLD, ABD and AGD, CLD is the smallest one (0.057�0.004 per cent). As far as the 20–40 cm soil layer was concerned, SLD had the largest SOM (0.131�0.005 per cent), and CLD has the lowest one (0.054� 0.004 per cent). No marked difference was found among

WLD, CLD, ABD, AGD and WOD.

Figure 3. Changes of total nitrogen (TN) under different land use types (error bars represent standard error). Different letters above barsrepresent statistically significant differences at P< 0.05 of the 0–20 cm and 20–40 cm soil layers, respectively. Note: WLD¼wasteland;


Figure 4. Changes of nitrate nitrogen (NON) under different land use types (error bars represent standard error). Different letters above barsrepresent statistically significant differences at P< 0.05 of the 0–20 cm and 20–40 cm soil layers, respectively. Note: WLD¼wasteland;


458 J. GONG ET AL.


Soil NON of the different land use types declined with soil depth increase (Figure 4). SLD had the highest soil

NON at both soil levels, WLD, CLD, ABD, AGD, WOD had a significantly lower soil NON concentration at both

soil levels in comparison with that of SLD, however, there was no significant difference amongWLD, CLD, ABD,

AGD and WOD.

No significant difference was observed in soil NHN content under different land use types (Figure 5). Although

land use types can affect soil NHN content, there was no significant difference among the six land use types in

either of the two soil layers. Soil NHN content of the 0–20 cm soil layer under different land use types was higher

than that of the 20–40 cm soil layer. It indicated that NHN may be easily accumulated by different land use or

vegetation restoration types since soil NHN is the positive ionic state of soil N and it can be easily transported.

Changes of Soil P Under Different Land Use Types

Land use and vegetation restoration had little effect on soil TP content (Figure 6). Although soil TP under different

land use types declined with soil depth, there was no significant difference in soil TP among all land use types in

either of the soil layers. SLD and WOD had lower soil TP content in the top 20 cm soil layer than WLD. However,

TP in the cropland or former cropland (ABD and AGD) was higher than that of SLD and WOD.

The effect of land use on the soil AP content was different (Figure 7). In the top 20 cm soil layer, CLD had the

highest AP content, and WOD has the lowest one. There was no significant difference in soil AP between WLD,

ABD and AGD, and no significant difference in soil AP between SLD and WOD. The appearance of higher AP

content in the soil of CLD may be attributed to the input of P fertilizer by farmers. In the 20–40 cm soil layer, no

significant difference was found between WLD, ABD, SLD and WOD, nor any significant difference between

WLD, CLD, ABD and AGD.

Changes of Soil AK Under Different Land Use Types

Soil AK under different land use types declined with soil depth increase, moreover, the effect of land use on soil

AK was different (Figure 8). In the top 20 cm soil layer, no significant difference was found between WLD, SLD

Figure 5. Changes of ammonium nitrogen (NHN) under different land use types (error bars represent standard error). Different letters abovebars represent statistically significant differences at P< 0.05 of the 0–20 cm and 20–40 cm soil layers, respectively. Note: WLD¼wasteland;




and AOD, nor between ABD, SLD and WOD. There was no significant difference in AK between CLD and AGD.

In the soil layer at 20–40 cm, CLD had the highest value. No significant difference was observed between WLD,

CLD, ABD, AGD and WOD. Compared with CLD, vegetation restoration had improved the content of AK. CLD

had a very low value since harvest would take AK away from soil. With the vegetation plantation, soil K was

absorbed and accumulated in the living organisms, which return K to soil.

Figure 6. Changes of total phosphorus (TP) under different land use types (error bars represent standard error). Different letters above barsrepresent statistically significant differences at P< 0.05 of the 0–20 cm and 20–40 cm soil layers, respectively. Note: WLD¼wasteland;


Figure 7. Changes of available phosphorus (AP) under different land use types (error bars represent standard error). Different letters above barsrepresent statistically significant differences at P< 0.05 of the 0–20 cm and 20–40 cm soil layers, respectively. Note: WLD¼wasteland;


460 J. GONG ET AL.


DISCUSSION

Change of Soil Nutrients Under Different Land Use Types

Our study demonstrated that land use change and vegetation restoration had significant effects on soil nutrients.

This is similar to other researchers (Lumbanraja et al., 1998; Rhoades et al., 2000; Priess et al., 2001; Liu et al.,

2002; Pamela et al., 2005). Land use change, for example, from natural vegetation to agricultural land, or from

grassland to arable land, can strongly impact soil carbon and nutrient concentrations. This is because (1) human

activities, such as tillage, harvest and vegetation plantation, could affect soil nutrient decomposition or loss; (2)

human disturbance may affect soil moisture by changing micro-climate and plant patterns (Davidson et al., 1993);

and (3) species have different nutrient requirements, exploit nutrients with varying efficiency and store or convert

nutrients at different rates (Aerts and Chapin, 2000).

Changes in land use affect input and output of nutrients and carbon in soils and vegetation. Vegetation

restoration, such as, shrub, tree and grass planting, and cropland abandonment may increase soil organic matter,

whereas crop production may decrease soil organic matter. Our study indicated that planting potatoes on the

wasteland depleted about 36�39 per cent of soil organic matter at the 0–40 cm soil layer, and planting peashrub

(C. korshinskii) increased soil organic matter by 75�28 per cent. This is because peashrub (C. korshinskii), a

leguminous plant, can improve soil nitrogen by N fixation, which may further improve soil conditions. Moreover,

better soil conditions are favourable to vegetation growth; which in turn produces more vegetation litter to enrich

soil C. This makes a beneficial cycle between soil and vegetation.

Significant differences were found in soil TN between the six land use types, while no significant differences

were found in either NON or NHN. Soil N of CLD, ABD and AGD was lower than that of WLD. In this study, soil

N of the 0–40 cm soil layer was increased after cropland converted into shrubland, wasteland, woodland and

grassland. This was due to different land use (vegetation) species having different N requirements, exploiting N

with varying efficiency and storing or converting N at different rates (Aert and Chapin, 2000; Chen and Li, 2003).

The distribution of soil N has a close relationship with root distribution (Berger et al., 2002). Many studies have

Figure 8. Changes of available potassium (AK) under different land use types (error bars represent standard error). Different letters above barsrepresent statistically significant differences at P< 0.05 of the 0–20 cm and 20–40 cm soil layers, respectively. Note: WLD¼wasteland;




found that nitrogen-fixing species can significantly increase soil N while others found no correlation between the

nitrogen-fixing species and total N accumulation in the surface soil (Cromack et al., 1999; Chen and Li, 2003). The

TN content of the soils showed variation between the land use types.

Differences in soil P storage may result from changes in biological and geochemical processes at different

depths after human disturbance (Lajtha and Schlesinger, 1988; Chen and Li, 2003). Soil TP did not significantly

change as CLD was converted into other land use types. However, a statistical difference was found in soil AP

among the six land use types. Soil AP was higher in the surface 20 cm soil layer in the potato fields, which may be

affected by fertilizer input. Larger variations in soil AP were found among different land use types. This is

consistent with the result of Verheyen et al. (1999).

Soil K was higher in WLD, ABD, AGD, SLD and WOD in comparison with that in CLD (potato field).

Therefore, cropland conversion into grassland, woodland and shrubland would improve soil K content. Vegetation

restoration had increased the accumulation of soil K because the nutrient-rich branches, twigs and coarse litter

fractions are important nutrient sources. The loss of K from litter was relatively rapid at the initial decomposition

stage (Liu et al., 2000), and more than 60 per cent of K was released from litter within six months and> 75 per cent

by the end of 12 months.

Enrichment of Vegetation Restoration on Soil Nutrients

Vegetation restoration and cropland abandonment had an enrichment effect on soil nutrients when compared with

cropland. This is because:

(1) Trees and shrubs function as natural barriers to reduce erosion (Wezel et al., 2000), especially in the field

where a litter layer exists. This means that there is less loss of soil nutrients due to runoff and wind under

shrubland, woodland and grassland than cropland.

(2) Soil nutrient enrichment of shrubs and trees might be due to ion uptake by root and accumulation of litter on

ground.

(3) Soil beneath woody plants was often referred to as ‘islands of fertility’, because soil conditions there are better

than they are under open wasteland. This results in a benign cycle for the biogeochemical process in the long

run.

(4) Trees and shrubs may also enhance above- and belowground microclimate, while meso- and microfauna and

microfora around plant roots may alter soil chemical, biological, and physical properties (Wilson and

Thompson, 2004).

Implications for ‘Grain-for-Green Policy’

Our study results showed that soil organic matter and TN contents exhibited significant differences in the six land

use types. The six land use types can be ranked by SOM decrease: shrubland>woodland>wasteland> artificial

grassland> abandoned land> cropland (Table I). Therefore, vegetation restoration, such as the planting of shrubs,

trees and grasses, could improve soil conditions and increase soil C sequestration. As for the ‘Grain-for-Green

Policy’ and ecological restoration in the loess hilly area, shrub planting and natural restoration (i.e. cropland

abandonment) are optimal choices for improving soil conditions. Although the forest has also increased soil

fertility and soil C sequestration, planting of trees is not the best choice for vegetation restoration due to the water

deficit in the study area, which belongs to a typical steppe zone (Wu and Yang, 1998). However, highly adaptable

trees can be planted and dotted about in the shrubs and grasses to increase biodiversity.

Implications for Sustainable Land Use and Economic Development

It has been highlighted that soil nutrient depletion, soil erosion and poverty are the main factors threatening future

soil productivity and consequently sustainable land use in the loess hilly area of China. Thus, several options exist

to mitigate the problems of land degradation induced by irrational land use.

462 J. GONG ET AL.


The first one is the conversion of slope farmlands into more sustainable land use types such as shrublands or

grasslands and it seems a most cost-efficient way for soil conservation and ecological restoration. Shrub planting

and cropland abandonment will be a win-win way to provide fertility improvement on the one hand and save

investment on the other. However, this requires alternative jobs for the large rural labour force. Alternatively,

terracing could be a promising choice because of its high efficiency both in soil loss reduction and crop yield

improvement.

The second option is the use of agro-techniques for soil conservation, such as furrow-ridging tillage, more C

input (e.g. manure addition and crop residues return), cropping in rotations with leguminous plants and rainwater

harvesting and supplemental irrigation farming (WHSI farming system) (Pandey 1991; Tian et al., 2003). It should

be noted that the WHSI farming system has an advantage over traditional rain-fed and runoff farming in increasing

crop yield of wheat, corn and potatoes (Tian et al., 2003). In the central area of Gansu Province, there are many

favourable conditions for growing potatoes, such as cool climate, loose soil, and a long history and great

experience. Therefore, developing potato production using WHSI will be the best investment opportunity.

The third option is to educate and train local farmers with high techniques. More education and training will

increase the opportunities for income. Moreover, the improvement of people’s perception of the environment will

be helpful in maintaining the achievement of and advances in ‘Grain-for-Green Policy’ (Lu et al., 2004). However,

development of off-farm employment to absorb the large surplus rural labour force and education are very

important for the sustainable development in the loess hilly area of China.

All in all, ‘Grain-for-Green Policy’, returning reclaimed farmland to forest/grassland, will not only improve the

environment and ensure sustainable development, but will also fill the farmers’ pockets in the long run. However, it

is impractical to convert all slope cropland to woodland or grassland and then import food supplies from other

provinces (Liu, 2001). Moreover, it is important to strengthen the achievements attained thus far by providing

sustenance to farmers, so that they will neither rely on the returned farmland for food nor cut trees in the reforested

areas for firewood in the future. Furthermore, the locals should contrive to improve the survival rate of the trees

planted in the returned farmland, and ensure farmers, who have been subsidized after giving up land for

reforestation, can still make a living after those subsidies cease. Nevertheless, if the people take full advantage of

all the potentials of the ‘Grain-for-Green Policy’ and continue to preserve the present terrace farmland, the food

supplies could support the regional population and all slope farmland could be abandoned eventually. Hopefully,

our study results may provide some useful guidance for the ‘Grain-for-Green Policy’ and sustainable land use in

the Loess Plateau, China.

CONCLUSION

Developing strategies that foster sustainable land use and management in the loess hilly area of Loess Plateau of

China poses a particular challenge. Our study showed that different land use types and vegetation restoration had

different effects on soil nutrients. Soil under different land use types has shown remarkable differences in several

properties, especially in distribution of C, N and P within the soil profiles. Improvement in SOM and nutrients

would be expected from more C inputs and alternative cultivation practices such as no/minimum tillage and

application of leguminous plants intercropping with other crops to ameliorate soil quality in the loess hilly area.

Vegetation restoration and cropland abandonment (natural restoration) may enrich soil nutrients. Different

vegetation species lead to differences in nutrient enrichment. Vegetation restoration, such as shrub, tree and grass

planting, and cropland abandonment, increased the content of soil organic matter, while crop production decreased

the content of soil organic matter. While crop production can significantly decrease soil fertility, it appears that the

trend can be reversed by cropland abandonment and afforestation. It can be suggested that it is better to change

cultivated land into shrubland or grassland for soil quality improvement in the loess hilly area of the Loess Plateau.

Natural restoration (i.e. cropland abandonment) may be another optimal way to provide ecological restoration of

the Loess Plateau. As for the sustainable land use and ‘Grain-for-Green Policy’ of China, it is recommended that

shrub planting and cropland abandonment, agro-techniques for soil conservation including furrow-ridging tillage,

leaving crop residues on field, cropping in rotation with leguminous plants and develop crop production using



rainwater harvesting and supplemental irrigation farming, education and techniques to train local farmers could be

used to control soil erosion, to improve the soil conditions, to advance the sustainable land use and development in

the loess hilly area in the Loess Plateau of China.

acknowledgements

This project was supported by the National Natural Science Foundation of China (40321101) and partially funded

by the National Advanced Project of the Tenth Five-year Plan of China (2001BA606A-03). Thanks are given to the

members of project team for field assistance, to the Institute of Soil and Water Conservation of Chinese Academy

of Sciences in Yangling for the laboratory analyses of the soil samples, to the Dingxi Institute of Soil and Water

Conservation for the provision of the meteorological data, and to two anonymous reviewers for useful comments

on the paper.

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