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V. Land Preparation and Crop Establishment Techniques

V. Land Preparation and Crop Establishment Techniques

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304

2.0



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b



1.5 b



Jz



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C



c



0 1.0



.-



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I



._C



-



a

a



FIG.5. Effect of previous land usage on grain yield of upland rice. (Adapted from Castin

et al., 1983b.)



that planting maize (Zea mays L.) or mungbean in the dry season reduced

weed growth and weeding time and increased herbicide performance and rice

yields in the following season as compared with plots kept weed-free by using

paraquat or being maintained as weedy fallow (Fig. 5). In plots where maize

was planted during the preceding dry season, yields were 1.6 tons/ha

compared to 1.3 and 0.7 ton/ha, respectively, in the mungbean and weedy

fallow plots.

OF SEEDBED PREPARATION IN DIFFERENT

REGIONS

B. METHODS



In Asia, little mechanization is used to prepare seedbeds. Fields are plowed

and harrowed with animal-drawn implements when rain falls (De Datta and

Ross, 1975). In Africa, upland rice fields are tilled manually.

Deep plowing is also a weed control method in upland rice. Curfs (1975)

found fewer weeds on soils that were deep plowed and rototilled with a

powerful tractor than on those that were shallow plowed or zero tilled. Pande

and Bhan (1966a) also showed the effectiveness of deep (28 cm) tillage in

reducing weed biomass and increasing panicle number and grain yield as

compared to tillage at 7, 14, and 21 cm (Fig. 6). At IRRI, Lopez et al. (1980)

and De Datta and Llagas (1984) reported that increasing the number of

rototillings reduced weed population, weed biomass, and weeding time

(Lopez et al., 1980) and increased grain yields.

c . REDUCEDTILLAGE

AND WEED GROWTH

Crops can be grown with minimum soil disturbance and reduced energy

inputs for cultural operations if herbicides are used to control weeds.



305



WEEDS AND WEED MANAGEMENT



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150 Nc.-45N-



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7



14



21



Tillage depth (cm)



28



0



g-15



-0



FIG.6. Effect of varying depth of tillage on panicle number and yield of upland rice and on

dry matter production of weeds. (Adapted from Pande and Bhan, 1966a.)



Minimum tillage and no tillage of riceland have produced inconsistent results

in the tropics. Lack of success has been attributed to the rapid regeneration of

perennial weeds and the failure of herbicide controls (Seth et al., 1971; IRRI,

1977; Moody and De Datta, 1977; Olofintoye, 1982; Castin et a/., 1983a,b;

De Datta, 1983).

Lacsina et a/. (1980) observed that consistent satisfactory performance of

herbicides is imperative if minimum or zero tillage is to be successful. Failure

to kill weeds by applying herbicides can be more detrimental to crop yield

than failure to control subsequent regrowth of weeds or to suppress later

weed emergence. Olofintoye and Mabbayad (1981a) reported a stand reduction with no tillage versus conventional tillage and that mulching without

tilling did not influence crop establishment.

Another land preparation method of weed control is the stale-seedbed

technique. After land preparation, weeds that emerge following rain are

destroyed by paraquat or tillage. The crop is then planted with minimum

disturbance of the soil. This method may reduce the need for later weedings

(Renaut, 1972). At IRRI (IRRI, 1979, 1980), the stale-seedbed technique

reduced weed weight but rice yields did not differ between weeded and

unweeded plots. However, in a subsequent study, Castin et a/. (1983a) found

that the stale-seedbed technique did not control weeds as well as conventional land preparation. Eliminating a particular weed species or weed

group encourages the buildup of other weed species.

D. THEEFFECTOF TIMEOF LANDPREPARATION



ON



WEED EMERGENCE



In rain-fed rice-growing regions, land is commonly fallow during the dry

season, during which weeds grow, complete their life cycle, and shed their



306



S. SANKARAN A N D S. K. DE DATTA



seeds or multiply vegetatively. A heavy weed cover at the start of the rainy

season hampers land preparation. In rain-fed agriculture, the time of land

preparation is vital to crop establishment and weed control. Soil cultivation

at different times of the year can influence the emergence, number, and species

of a weed community. Studies in IRRI uplands during the 1979 wet season

(Castin and Moody, 1980) showed that weed population in land prepared in

May was always higher than in land tilled in March or April, irrespective of

weed control treatments within the first 2 weeks after seeding.

Curfs (1975), at the International Institute of Tropical Agriculture (IITA)

in Nigeria, found no difference in the weed species or density and rice yield

due to different times of tillage, whether the main tillage operation was

carried out at the beginning of the wet season, just before seeding, at the end

of the wet season, or at the end of the dry season.



VI. FERTILIZER APPLICATION AND WEED MANAGEMENT

Of the major plant nutrients, nitrogen is usually the first to limit growth

(Blackman and Templeman, 1938). Pande and Bhan (1966b) and Chakraborty (1973) showed that weed species absorbed more nitrogen and phosphorus than upland rice at all rice growth stages.

The extent of nutrient competition differs with the time and method of

fertilizer application, even if the same quantity is applied at different times.

Fertilizer application should be timed to prevent weed proliferation and

maximize benefit to the crop. Where effective weed control is impossible,

nitrogen application should be delayed until weed nitrogen uptake has

slowed so more will be taken up by the competing rice crop (Matsunaka,

1970). However, the effectiveness of this recommendation depends on crop

growth stage.

Noguchi and Nakayama (1978) found that weeds grew better in the crop

row when fertilizer was band placed. Weeds between rows grew better with

broadcast fertilizer (Table VIII). Soundararajan and Mahapatra (1978) also

reported that the highest rice yield was obtained when nitrogen was applied

in split doses and fields were repeatedly hand weeded.

Riyanto (1977) observed that weed weight did not respond to the rate or

time of nitrogen application. Similarly, yield reduction caused by weeds was

not influenced by basal or split application of fertilizer. Singh et al. (1975)

reported no difference in weed population due to nitrogen placement in

upland rice. The same workers also observed that broadcasting nitrogen

promoted weed growth and rice yield.



307



WEEDS AND WEED MANAGEMENT

Table VIII

The Effect of Weed Location and Fertilizer Placement Method on

Weed Dry Weight"

Weed weight (g/m2)

Fertilizer placement

method

Band

Broadcast



a



Weed

location



Digitaria

ciliaris



Portulaca

oleracea



Cyperus

microiria



Intra-row

Inter-row

Intra-row

Inter-row



0.55



0.18

0.08

0.30

0.69



0.03

0.01

0.04

0.09



0.25

0.18

0.48



Adapted From Noguchi and Nakayama (1978).



The amount of nitrogen applied to rice influences competition for nutrients. De Datta (1977a,b) suggests that applying less fertilizer than is needed

to produce maximum yield is better when weed control is inadequate. This

recommendation emanated from the observation that yield loss caused by

weeds is greater at low and high rates of applied nitrogen than at intermediate levels. However, Pande and Bhan (1966b) reported that rice yields

almost doubled when nitrogen application was increased from 60 to 80 kg/

ha, indicating that rice was more competitive with more available nitrogen.

Without weeds, rice yield increases with fertilizer application. However,

Okafor and De Datta (1976b) obtained greater yield increments in nonweeded controls than in weeded plots when nitrogen application increased.

As the nitrogen rate increased, the percentage of yield loss due to weeds

decreased. De Datta (1977a,b) concluded that, in many cases, the yield of the

nonweeded fertilized plot was considerably lower than that of the weeded

plot without fertilizer. The first half of the growing season is the most

important in the competition for nitrogen (Chakraborty, 1973).

Seedbed preparation for upland rice significantly has a great bearing on the

time and method of nitrogen application (Olofintoye, 1980). Under conventional tillage, weed weight was greater when nitrogen was applied in split

doses (Table IX). With zero tillage, basal nitrogen application yielded

maximum weed biomass. There was no difference in weed weight in the staleseedbed technique, irrespective of time of nitrogen application. Pande and

Bhan (1966b) and Singh and Sharma (1981) reported that weed density and

biomass and soil nitrogen depletion increased as row spacing increased.

Okafor and De Datta (1976a,b) found that rice yield losses caused by

competing C. rotundus in uplands were greater for IR442-2-58than for IR5.



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