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VI. Fertilizer Application and Weed Management

VI. Fertilizer Application and Weed Management

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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.



S. SANKARAN AND S. K. DE DATTA



308



Table rX

The Effect of Land Preparation Method and Time and Method of

Fertilizer Application on Weed Weight at Harvest of C-22 Rice"

Weed weight (g/m*)

Time of N applicationb



Placement methodb



Land preparation



Basal'



Splitd



Band



Broadcast



Zero tillage

Stale seedbed

Conventional tillage



656 e

261 c

30 a



420 d

301 c

84 b



435 c



641 d

282 b

59 a



281 b

55 a



'Adapted from Olofintoye (1980).



* Within a time or method of nitrogen application in a column or row, means followed

by a common letter are not significantly different at the 5 % level.

' All nitrogen was applied at seeding.

dOne-third of the nitrogen was applied at seeding, one-third 15 days after seeding

(DAS), and one-third 50 DAS.



Applying nitrogen fertilizer to upland rice influenced the composition of

the weed flora in the field. For example, the broadleaf weed population

increased from 62% before nitrogen application to 82% with 90 kg N/ha

applied (CRIA, 1976).

In the early wet season, Okafor and De Datta (1976b) found that yield

reduction caused by C. rotundus was greater with fertilizer than without. In

the late wet season, yield decline caused by C. rotundus was greater with

fertilizer application, but there was no difference between nitrogen levels. In

the dry season, yield loss increased with nitrogen level.

Noguchi and Nakayama (1978) reported that the response of D. ciliuris,

Chenopodium album L., P. oleracea, Cyperus microiria Steud., and A . lividus to

fertilizer was greater than that of upland rice. They responded more in the

early and middle growth stages than at later stages.

Studies in the Philippines and Thailand emphasized the close relationship

between fertilizer inputs and weed control. The benefits of added fertilizer

increased markedly with better weed control (IRRI, 1973). De Datta and

Malabuyoc (1976) wrote that weed infestation and control affected the

nitrogen response of modern varieties of rice. This contention was further

substantiated by experiments at IRRI and in farmers' fields. Data averaged

from two locations showed that the nitrogen responses of IR20 during the

1973 wet season and the 1974 dry season were greater with than without

weed control. Fagade (1979) also reported that upland rice grown with low



309



WEEDS AND WEED MANAGEMENT

Table X

Effects of Nitrogen Application and Weeding on Grain Yield

of Upland RiceaFb



Grain yield (tonha)

Nitrogen applied (kg/ha)

Treatment



0 kg N/ha



30 kg N/ha



60 kg N/ha



Mean



No weeding

Propanil at 14 DAS

Hoeweeding at 14 and 28 DAS

Hoeweeding at 14,28, and 40 DAS

Propanil at 14 DAS + hoeweeding at

40 DAS

Mean



0.4

2.6

2.6

3.1

3.6



0.7

2.5

2.4

3.1

4.0



0.7

2.5

2.4

3.2

4.2



0.6

2.5

2.4

3.1

3.9



3.1



3.2



3.2



a



Adapted from Fagade (1979).

C.V. = 12%.



weeding levels did not respond to nitrogen application, but yield increased

between 1 1 and 15% with nitrogen application under high weeding levels

(Table X).

With an efficient weed control program it is possible to increase the

fertilizer use efficiency of the crop. When limited fertilizer is available, the

productivity per unit of applied fertilizer can be maximized by good weeding

practice.

The economics of upland rice farms limits herbicide use. Herbicides are

expensive and can (not all do) create toxic residues. Several herbicide-fertilizer mixtures have successfully reduced the herbicide rate and maintained

efficiency and selectivity.

Sankaran et al. (1974) reported that crop yield increased significantly when

butachlor and urea were applied compared with applying butachlor alone.

However, weed control efficiency was not significantly increased by adding

urea.

2,4-D and urea or ammonium sulfate effectively controlled weeds in upland

rice (Mukhopadhyay et al., 1971). Mani et al. (1973) observed improved rice

growth after a low rate of 2,4-D and 4-(chloro-o-tolyloxy)butyric acid

(MCPB) was applied with urea. Kaushik and Mani (1980) reported that the

herbicide rate could be reduced 50% when MCPB was applied with a 3%

urea solution. However, Sankaran et al. (1974) found that adding urea to 2,4D did not affect the efficiency and selectivity of the herbicide.



3 10



S. SANKARAN AND S. K. DE DATTA



A propanil-urea mixture was more efficient and selective on upland rice

than propanil alone (Patro and Tosh, 1975),despite a slight phytotoxic effect

on the crop. Mukhopadhyay et al. (1971) and Kaushik and Mani (1980)

showed that the herbicide rate could be reduced without affecting efficiency

by using a propanil-3% urea mixture. Sankaran et al. (1974), on the other

hand, reported that a propanil-urea mixture controlled weeds better but did

not influence crop yield.



V I I. S 0 IL M0 IST U R E- H E R B I CI D E R E LATI0 NS H IPS IN

UPLAND R I C E



A. RAINFALLDISTRIBUTION

AND WEED EMERGENCE



Competition for soil moisture may begin early, particularly in low-rainfall

areas (Sharma et al., 1977). More weeds emerge earlier at high soil moisture

than at low moisture level (Yamamoto and Ohba, 1977). Janiya et al. (1983)

reported that soil moisture from 0 to 15 cm had pronounced effects on weed

species emergence 4 weeks after land preparation. The pattern of weed

emergence varies with the time of land preparation and is largely influenced

by the frequency and amount of rainfall.



B.



SOIL



MOISTURE

CONTENT A N D HERBICIDE

ACTIVITY



Soil moisture status in upland rice influences not only weed emergence but

also the amount of herbicide in solution. Applying herbicides to upland

seedbeds with dry soil or when dry conditions follow immediately afterward

reduces the herbicide effectiveness (Indhaphun et al., 1979; Schiller and

Indhaphun, 1979, 1980). Jikihara and Kimura (1979) observed that herbicidal activity was higher in wet than in dry soil. The soil moisture content at

and after herbicide application (Sahu, 1978) and the solubility of herbicides in

water (Chen and Chen, 1979) determine the efficiency of soil-applied herbicides.

Olofintoye and Mabbayad (1981b) reported that frequent watering after

postemergence application of butachlor caused the herbicide to leach, in

toxic amounts, into soil zones where rice seeds were germinating. In India,

Sahu (1978) observed that soil moisture content exceeding 30% increased the



WEEDS A N D WEED MANAGEMENT



311



depth of butachlor movement and the susceptibility of emerging crop

seedlings. In the Philippines, Sankaran and De Datta (1984) found that a soil

moisture content of 35% or more increased the herbicidal activity of

butachlor, oxyfluorfen, and oxadiazon in upland rice. Nako (1977) observed

that increased soil moisture content after applying thiobencarb decreased

establishment and inhibited rice growth at the seedling stage. In very dry soils

in Bolivia, Tollervey et al. (1980) observed that pendimethalin did not

effectively control R.exaltata.

Rao and Dubey (1977) reported that high soil moisture caused severe

toxicity with dinitramine, piperophos plus dimethametryn, and butachlor;

moderate toxicity with nitrofen; and low toxicity with thiobencarb. Jikihara

and Kimura (1979) reported that thiobencarb 50% plus prometryn 5 % at 8

liter/ha gave excellent weed control in wet soil but not in dry soil.

Sankaran and De Datta (1984) reported that soil moisture status determined the success of chemical weed control in upland rice. During the 1983

dry season, they used a line-source sprinkler system to regulate soil moisture

while evaluating the effectiveness of pendimethalin and oxadiazon. With both

herbicides, IR36 yields were similar to those of the hand weeded check at

high moisture levels (81 1 and 691 mm). When moisture levels dropped below

cumulative pan evaporation (688 mm), yields with chemical and hand

weeding were similar to those in the unweeded check (Fig. 7). Below 525 mm

there was no grain yield, although use of herbicides and hand weeding

effectively controlled weeds.



FIG.7. Effect of herbicides on grain yield of upland rice IR36 at different moisture regimes.

(From Sankaran and De Datta, 1984.)



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