Comparative Performance of Different Weed Management Practices in System of Rice Intensification

A field study was conducted at Agricultural

In India, rice is the most important staple food for over two thirds of the population. It is a means of livelihood for millions of rural households and it plays a vital role in our national food security, hence the slogan "Rice is Life' is most appropriate. In India, rice occupies an area of 42.3 million ha with an annual production of 87.0 million tonnes and a productivity of little more than 3 tonnes ha-1. Rice is being grown extensively in the state of Andhra Pradesh in 4.0 million ha with an annual production of 17.8 million tones.
System of Rice Intensification (SRI) is worth studying as alternative to the conventional system of rice cultivation especially in situation of limited resource availability (Irrigation with ground water). Successful crop production under SRI method depends upon the effective weed management practice. In SRI method mechanical weed control by cono weeder is in vogue. Presently farmers are controlling weeds in SRI method of cultivation mechanically by using of cono weeder. In heavy soils running cono weeder in between rows is a hard task and moreover labourers are reluctant to operate this equipment because of requirement of more energy for operating this equipment. In this context, the chemical and cultural method of weed management has to be evaluated under system of rice intensification. Keeping this in view, the present experiment was designed and proposed for evaluation.

Materials and Methods
A field experiment was conducted during kharif 2008-09 at Agricultural Research Station, Kampasagar, Andhra Pradesh, India. The soil of the experimental site was sandy clay loam with pH 7.6. The nutrient status was medium in available N (282 kg N ha -1 ) and available phosphorous (22.5 kg P2O5 ha-1) and high in available potassium (305 kg K 2O ha-1). The experiment was carried out in a randomized block design with eight weed management treatments (T 1-Pre emergence application of butachlor @ 1.5 kg a.i ha-1, T2-cono weeding (CW) thrice at 15 days interval, T3 -Pre emergence application of butachlor @ 1.5 kg a.i ha-seedlings, nursery beds were thoroughly irrigated. After lifting, seedlings were immediately transplanted in the main field. The main field was prepared by ploughing twice followed by thorough puddling. The farm yard manure @ 15 t ha-1 was applied during first pudding in the main field. The fertilizers of N, P2O5 and K2O were applied at 120:60:40 NPK kg ha-1. The entire phosphorous and half of the recommended potassium were applied as basal dose during transplanting and another half of recommended potassium was applied during panicle initiation stage. Nitrogen was applied in 3 equal splits at transplanting, active tillering and panicle initiation stages.
Seedlings of 12 days old were transplanted in the main field in square pattern with a spacing of 25 x 25 cm with single seedling per hill. Field was irrigated just enough to saturate the soil with moisture. Subsequent irrigation was given as the soil starts forming fine cracks throughout vegetative phase. From flowering to 10-12 days before harvesting, a thin film of water was maintained continuously by frequent irrigation. During cono weeding, standing water was maintained to facilitate for easy movement of conoweeder. Weed management was done as per the treatments. Cono weeder was run at 15 DAP for thrice at 15 days interval.
The observations on yield attributes like panicle number m-2, panicle length, panicle weight, filled and unfilled grains per panicle and 1000 grain weight and grain yield were recorded at harvest. Weed density and weed dry matter were recorded and weed control efficiency was worked out.

Weed density, weed dry matter and weed control efficiency
Weed density and weed dry matter at flowering stage were significantly lower under integrated weed management practice of butachlor @ 1.5 kg a.i ha-1 combined with cono weeding thrice at 15 days interval and hand weeding at 20 and 40 DAP (Table   1) and it was comparable with hand weeding at 20 and 40 DAP combined either with butachlor @ 1.5 kg a.i ha-1 or cono weeding thrice at 15 days interval and butachlor @ 1.5 kg a.i ha-1+ cono weeding thrice at 15 days interval.

Yield attributes
Panicle number, filled grains, panicle length and 1000 grain weight were significantly higher in integrated weed management practice of butachlor @ 1.5 kg a.i ha-1 combined with cono weeding thrice at 15 days interval and hand weeding at 20 and 40 DAP than the weedy check, butachlor @ 1.5 kg a.i ha-1 alone and cono weeding thrice at 15 days interval (Table 2). Panicle number recorded in hand weeding at 20 and 40 DAP combined either with butachlor @ 1.5 kg a.i ha-1 or cono weeding thrice at 15 days interval and weed free practices were comparable with each other and significantly higher than the butachlor @ 1.5 kg a.i ha-1 and un weeded check.
Filled grain per panicle recorded under conoweeding thrice at 15 days interval combined either with hand weeding at 20 and 40 DAP or butachlor @ 1.5 kg a.i ha-1 and weed free were on par with integrated weed management practice of butachlor @ 1.5 kg a.i ha-1 combined with cono weeding thrice at 15 days interval and hand weeding at 20 and 40 DAP and significantly higher than the butachlor @ 1.5 kg a.i ha-1 and un weeded check.
Panicle length observed in pre emergence application of butachlor @ 1.5 kg a.i ha-1 + cono weeding (CW) thrice at 15 days interval or hand weeding at 20 and 40 DAP, cono weeding (CW) thrice at 15 days interval + HW at 20 and 40 DAP and weed free check were comparable with each other and significantly higher than the butachlor @ 1.5 kg a.i ha-1 and weedy check. Integrated weed management practice of butachlor @ 1.5 kg a.i ha-1 combined with cono weeding thrice at 15 days interval and hand weeding at 20 and 40 DAP resulted significantly higher 1000 grain weight than the butachlor @ 1.5 kg a.i ha-1, cono weeding thrice at 15 days interval and butachlor @ 1.5 kg a.i ha-1 combined either with cono weeding thrice at 15 days interval or hand weeding at 20 and 40 DAP. It is comparable with hand weeding at 20 and 40 DAP combined with conoweeding thrice at 15 days interval and weed free check. Integration of weed management practice helps in better control of weed growth, there by less competition for resources which leads to good crop growth and yield attributes than the single weed management practice.

Grain yield
Integrated weed management practice of butachlor @ 1.5 kg a.i ha-1 combined with cono weeding thrice at 15 days interval and hand weeding at 20 and 40 DAP resulted in higher yield attributes due to broad spectrum control of weeds cum reduced weed dry weight which to more nutrient uptake, exposure to sunlight and weed free condition at the early stages of crop growth. The weed free condition at critical stages of crop might have favoured increased panicle number and length, filled grains and 1000 grain weight due to increased availability of nutrients with less competition. Which ultimately resulted higher grain yield.
Grain yield was significantly higher in integrated weed management practice than the butachlor @ 1.5 kg a.i ha-1, conoweeding thrice at 15 days interval and unweeded check ( Table 2). The grain yield recorded in weed free check and hand weeding at 20 and 40 DAP combined either with butachlor @ 1.5 kg a.i ha-1 or cono weeding thrice at 15 days interval were on par with integrated weed management practice. The same results were confirmed by Subramanian et al. (2006), Kavitha et al. (2010) and Latif et al. (2005).
Higher gross returns and B.C ratio were registered in butachlor @ 1.5 kg a.i ha-1 combined with cono weeding thrice at 15 days interval and hand weeding at 20 and 40 DAP. In cono weeding (CW) thrice at 15 days interval + HW at 20 and 40 DAP and weed free check were registered similar gross returns and B.C ratio with that of integrated weed management practice.

Conclusion
It could be concluded that butachlor @ 1.5 kg a.i ha-1 combined with cono weeding thrice at 15 days interval and hand weeding at 20 and 40 DAP resulted in higher grain yield, gross returns and B.C ratio. in system of rice intensification.