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V. Problems in Multiple-Cropping Systems

V. Problems in Multiple-Cropping Systems

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354



GUO YI XIAN AND FEI HUAI LIN



A. GROWING

SEASON

STRESS

In expanding triple-cropping systems in original double-cropping regions,

particularly in the border area, or expanding double-cropping systems in

original single-cropping regions, the first problem met was the stress of the

growing season. The total growing duration for double-rice three-crop

systems was 420-460 days a year in Zhejiang Province and the Suzhou

Prefecture of Jiangsu Province (of which green manure occupied 180 days,

rapeseed 220, barley 190, and double rice 250 days). There was a deficit of 55

to 100 days a year. In Beijing Municipality, the total duration of the

wheat-rice cropping system amounted to 410 days (of which wheat needed

250 days and rice 160 days), resulting in a deficit of 45 days a year. Even if

seedlings were raised in a nursery, or green manure was undersowed

(Astragalus and common vetch) before harvest of the rice, the growing season

was still not long enough. Harvesting the previous crop and planting the next

one must be done within 5-10 days (Fig. 10). As Fig. 10 shows, in Suzhou

Prefecture the first crop of rice does not ripen until the beginning of August,

and the second crop of rice must be transplanted not later than August 10-12.

Any delay would be bound to cause a sharp yield reduction or even the loss of

harvest in cold years.



B. DETERIORATION

OF SOIL PHYSICAL AND CHEMICAL PROPERTIES

Studies by the Shanghai, Zhejiang, and Guangdong Academies of Agricultural Sciences of cropping systems and soil fertility showed that the contents

of organic matter, total nitrogen, and total phosphoros in soil under doublerice three-crop systems were higher than that under double-cropping systems

before they were changed. Similar results (Table I) were obtained by the

Guangdong Academy of Agricultural Sciences in experimental plots. Contents of organic matter, total nitrogen, and total phosphorus in soil under a

wheat-rice-rice system for 3 years were higher than those under a rice-ricefallow system. These results illustrate the effects of greater organic and

chemical fertilizer applications in triple-crossing systems.

However, because the waterlogging period of the fields under double-rice

three-crop systems is about 40 days longer than those under wheat-rice

systems, and also because of successive plowing and harrowing in the wet

conditions each year, the tillage layer of the soil is shallower and the plow pan

is thicker. Investigations in the Suzhou Prefecture of Jiangsu Province by the

Nanjiang Soil Institute of the Chinese Academy of Sciences indicated that

double-rice three-crop systems obviously reduced the contents of microaggregates and the total soil porosity, resulting in low permeability and low



355



RICE-BASED CROPPING SYSTEMS

Table I

Comparison of Some Major Soil Nutrients Before and After Changing

of Cropping Systems

Organic

matter



Total

nitrogen



Total

phosphorus



(%I



( %)



( %I



Before change

After change



4.54

5.10



0.248

0.27 1



0.119

0.156



Shanghai

AAS



Before change

After change



2.80

3.51



0.188

0.190



0.213

0.239



Zhejiang

AAS



Rice-rice, 3-yr plot

Wheat-ricerice, 3-yr plot



1.32

1.53



0.076

0.080



0.048

0.059



Guangdong

AAS



Status



Source of

data



availability of nitrogen. The soil nutrients released failed to meet the demands

of the rice. Investigations in Wuxi County of Jiangsu Province in 1975 and

1976 revealed that in the “yellow mud” soil, the release of soil nitrogen was

not apparent until mid-June to late July and did not reach a peak until early

August to mid-September. This was much later than the peak of the nutrient

requirement of the first crop of rice, so extra chemical fertilizers had to be

applied.



C . PESTPROBLEMS



High cropping intensity brought about obvious changes in insect fauna

and the population dynamics of major insect pests. The yellow stem borer,

striped rice stem borer, and rice plant skipper were the major insect pests of

rice in China. From 1957 to 1968, at the early stage of cropping system

reformation, the diversified cropping systems such as green manure-rice and

fallow-rice-rice had been practiced together in the same region. Early-,

medium-, and late-maturing varieties provided a whole range of feeding

cycles for these pests. Reports from the Jiangsu Academy of Agricultural

Sciences indicated that the stem borer damage reached a peak record in this

stage. The rate of “white panicle” caused by the stem borers on mid-seasoned

Japonica varieties averaged 3-5% in general and 10-30% in prevalent years.

By 1976, when double-rice three-crop systems became predominant in this

area, land preparation for the first and second crop of rice cut off the stem

borers’ life cycle, resulting in a reduction of third-generation density and

hence the pest became less serious. Since the readjustment of rice-based

cropping systems started in 1979, and since the original wheat-rice system



356



GUO YI XIAN AND FEI HUAI LIN



was expanded again (especially where hybrid rice cultivators were grown

after wheat), the damage of stem borers has risen again.

Brown plant hoppers and rice leaf folders were incidentally occurring

insect pests in the past. Since double-rice three-crop systems were developed,

they have become major pests in Central China. Outbreaks of brown plant

hopper and rice leaf hopper occurred only 1 year in 20 during the period of

the 1950s and 1960s, and 7 and 6 years, respectively, in the most recent 12

years. Since 1980, the white-backed plant hopper has exerted more serious

damage on early and middle rice than on late rice and on Indica varieties

than on Japonica varieties.

With increases in cropping intensity, rice diseases became more serious.

Seedling rot of the first crop of rice (due to advanced sowing date), neck blast

of the second crop of rice (due to delayed heading date), and sheath blight due

to heavy fertilizer applications and vigorous vegetable growth all occurred

more often. In addition, some virus diseases were spread by the brown plant

hopper and the white-backed plant hopper.

D. STRESSIN LABORUTILIZATION

Raising cropping intensity not only increased the total demand for field

labor, but concentrated the demand at certain time intervals. The level of

agricultural mechanization is still low, particularly in the rice-growing

regions. According to the results of surveys in Wuxi County of Jiangsu

Province, the annual labor demand of double-rice three-crop systems

amounted to 1477 man-days/ha. This was 330 man-days or 13% more than

that for double-cropping systems. Moreover, most of the labor demand was

concentrated in the field turnaround periods, forming three peaks in a year. It

is particularly busy in late July to early August, the interval between

harvesting the first crop of rice and planting the second crop of rice, because

all the field work must be done within 5 to 10 days. In spite of the fact that

China has a large population and limited arable land, and that the highcropping-intensive areas are always matched with dense population (even in

the delta of the lower reach of the Yangtze River, where per capita arable land

is only about 700 m3), the farmers must work 12 h/day during that period to

strive for planting all the rice fields on time.

E. DECLINE

OF THE FARMERS

AGRICULTURAL

NETINCOME



In order to maintain the existing yield level or to gain further increases in

yield, farmers have to use extra fertilizers, pesticides, and labor. But the rate of



357



RICE-BASED CROPPING SYSTEMS



Table I1

Annual Grain Yield and Material Cost in Double

and Triplecropping Stages



Jiading County



Wuxi County



Period



Yield

(kg/ha)



cost

(U.S.$/ha)



Yield

(kg/ha)



cost

(U.S.$/ha)



Double-cropping stage

Triple-cropping stage

Increase (%)



5250

9278

76.7



247

612

147.4



6383

9010



239

617



41.1



158.1



increase in yields often lags behind the increasing rate of costs. Consequently,

the agricultural net income decreases. This situation restrain farmers’ initiative in multiple-crop farming.

The results of investigations in Jiading County of Shanghai Municipality

and Wuxi County of Jiangsu Province (Hua, 1983), Table 11, shows that grain

yield per hectare in double-rice three-crop systems (1979) increased 76.7%

and 41.1% in Jiading and Wuxi, respectively, as compared with those in the

double-rice-cropping stage (1965). But the material costs per hectare increased 147.8% and 158.3% in 1979 as compared with 1965. As a result, the

grain material cost per kilogram varied from 4.7 and 3.7 U.S. cents in 1965 to

6.6 and 6.8 cents in 1979 in Jiading and Wuxi, respectively.

Investigations of the Chinese Association of Agricultural Sciences indicated that during the period from 1975 to 1979, when the double-rice threecrop system covered almost all the paddy fields in Wuxi County, the county

agricultural net income averaged 30.5 million U.S. dollars per year. This was

22.2% less than that in 1966, when the double-rice three-crop systems

covered only about 20% of total paddy fields in the county. Consequently,

the proportion of paddy fields covered by double-rice three-crop systems in

Suzhou Prefecture (Wuxi County included), one of the most croppingintensive regions in China, decreased year by year from the peak of 85.9% in

1976 to 48.4% in 1981.

F.



SHORTAGE OF VARIED



FEEDS

FOR LIVESTOCK



The reformation of rice-based cropping systems tended to overemphasize

the growing of rice, wheat, barley, and rapeseed and ignore the role of maize,

soybean, and other upland crops in multiple-cropping systems. Moreover, we

emphasized the expansion of triple- and double-cropping systems in areas

where originally double- and single-cropping systems, respectively, had



358



GUO YI XIAN A N D FEI HUAI LIN



prevailed. Some original sound systems were abandoned. Therefore, the

cropping systems and agricultural products became such as to force farmers

in the Central China and South China rice belts to feed milled rice to swine

and buffalo. It was reported that in Hunan Province, the amount of rice used

for feed increased to about 250,000 tonfyr. The high cost and low feed

efficiency of milled rice restrained livestock production in the countryside.



VI. APPROACHES TO SOLVING THE PROBLEM

Because these above problems had occurred, readjustments of rice-based

cropping systems were started in 1978. The cropping intensity in some places

has been reduced and the problems have been solved to a certain extent, but

grain production has also decreased. In the long run, as China is a country

with a large population in relation to its arable land area, lowering cropping

intensity is not the best approach, except in some individual districts where

the reformation of cropping systems has gone too far in increasing cropping

intensity. The major challenge facing us is to solve promptly these problems

and to continue to increase crop production. The main approaches to solving

the problems are discussed below.



A. MAKINGRATIONALUSEOF VARIEDCROPPING

SYSTEMS

It is recognized that, depending on local environmental conditions, we

must make rational use of varied cropping systems to increase agricultural

production. Sichuan Province has provided a good example (Fig. 11). Since

the middle 1950s, the double-rice system has been expanded in this province,

the peak acreage mounting to 556,000 ha (15.2%) in 1975. But the yield

performance was much better on the fields of high-yielding production teams

than it was on the farmers’ fields. For example, the yields of the double-rice

system averaged 10.6 ton/ha, or 4.6 ton/ha more than that of middle-season

hybrid rice in Ren-Min production team trials of Fushun County. But the

provincial average was only 1.1 ton/ha more (Table 111). Thus the provincial

authorities encouraged the farmers to reduce the acreage of the double-rice

system and to raise the acreage of wheat-rice double-cropping systems. At

the same time, they expanded the area of hybrid rice cultivars after wheat.

Remarkable success has been obtained. In 1980, the acreage of the doublerice system was reduced to about 10,000 ha, i.e., 20.3% of that in 1975. The

yield of rice averaged 5.02 ton/ha, i.e., 34.6% more than that in 1975. The

provincial rice production by 1980 had increased by 1.76 million tons, despite



359



RICE-BASED CROPPING SYSTEMS



-



Area



Yield



5.0



.



LO m

r

C



1.0



c

2



3.0 j--



973



1974



1975



1976



1977



1978



1979



1980



FIG.11. Area of double cropping of rice and provincial rice yield in Sichuan.



the fact that the cropping acreage had decreased 588,800 ha (16.1 %) as

compared with 1975.

Taoyuan County of Hunan Province provided another good example.

There were 20,000 ha of double rice located in the areas with high altitude

and with water and labor deficiency. By 1982, more than 10,000ha had been

transferred to wheat (or rapeseed, or green manure)-rice systems, resulting in

an increase of 10,496 tons of grain and a benefit of 4.8 million U.S. dollars.

According to the results of long-term cropping systems experiments

conducted by the Hubei, Hunan, and Jiangxi Academies of Agricultural

Sciences, the rotation systems (green manure-rice-rice followed by rapeseed-rice-rice, wheat-rice-rice, and board bean-rice-rice in four years)

showed a higher yielding potential, better nitrogen efficiency, and greater

Table 111

Comparison of Yields of Double-Cropping Rice

and Middle-Season Rice in the Sichuan Basin



Location



1st crop



2nd crop



Total



Yield of

middle rice

(tonha)



Western part

Central part

Southern part

Eastern part



4.52

3.79

3.95

3.58



2.18

1.73

1.64

1.82



6.70

5.52

5.59

5.40



5.41

4.38

4.59

4.28



Mean



3.96



1.84



5.80



4.67



Yield of double rice (ton/ha)



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