India is the second largest producer of potato in the world, contributing ≈10% of the world’s potato production. In 2012, potato was cultivated on 1.87 million hectares in India, with a production of 41.3 million tonnes (Government of India, 2013). Punjab is one of the largest potato producing states in India. In fact, potato cultivation occupies nearly 50% of the total area of vegetable crops in Punjab. Potato is a short duration crop; therefore, it fits in rotation with cereals, vegetables, pulses, or oilseed crops. Weed management is a challenge for potato producers because of a scarcity of labor for hand weeding and limited options for registered herbicides. Weed interference with the crop reduces marketable yield by decreasing potato tuber number and size (Ahuja et al., 1999; Dallyn 1971; Nelson and Thoreson, 1981; Singh and Bhan, 1999). Weeds may also hinder mechanical harvest (Pandey, 2000; Wall and Friesen, 1990).
Critical period of weed control in potato is 20 to 66 d after emergence under irrigated conditions (Monteiro et al., 2011). Potato growers usually apply herbicide early postemergence and then it is followed by earthing up (inserting soil on both sides of the ridge with tractor-drawn implements, reshaping the ridges and covering potato roots and emerging tubers from direct sunlight), which also helps suppress late-emerging weeds. In the case of grass weed infestation, including littleseed canarygrass and wild oat (Avena fatua) at later stages, growers have been using graminicides. Hence, weed management programs in potato usually include at least one herbicide application and a mechanical operation in Punjab.
Potato growers in northwest India rely on triazine herbicides for weed control. Atrazine, a triazine herbicide, is applied preemergence as well as postemergence to control several broadleaf and some grass weeds primarily in maize (Zea mays), sorghum (Sorghum bicolor), and sugarcane (Saccharum officinarum). Atrazine is also applied in other minor crops, such as potato in India. However, sometimes atrazine persists for a long period of time in the soil and injures vegetable and pulse crops grown in rotation with potato. Potato is a winter season vegetable, planted in mid-September to early October and harvested in January or February in northwest India. Lower temperatures during potato growing season increase the persistence of herbicides, including atrazine. Growers planting vegetable crops after potato harvest have reported atrazine injury in rotational vegetable crops, especially in cucurbits, one of the major spring and summer vegetable crops in northwest India. Atrazine applied at 2 kg·ha−1 in maize seeded in the first week of September resulted in the injury to the wheat (Triticum aestivum) crop seeded in the first half of November; with an interval of <75 d between atrazine application and seeding wheat (Sharma and Sandhu, 1985). Metribuzin at 350 g·ha−1 applied to potato suppressed the growth of mung bean (Vigna radiata) seeded in mid-March (M.S. Bhullar, unpublished data). An effective long-term alternative to triazine for weed management in potato has not been identified.
Overreliance on herbicides and an increased emphasis on sustainable weed control practices, have renewed interest in environmentally benign methods of weed management that rely less on chemicals. In addition, the evolution of herbicide-resistant weeds has renewed interest in the use of nonchemical approaches to suppress weeds. Cultivation and herbicides are the most commonly used weed control methods in potato (Callihan and Bellinder, 1993). Manual hoeing is quite effective but not much effective, since it may cause root injury and disturbs root systems, if performed in the later stages of plant growth (Khurana et al., 1993). Properly timed straw mulch can suppress early germinating annual broadleaf and grass weeds and will be sustainable for a long period of time. Mulch, whether living or dead, inhibits the light necessary for weed shoot emergence and growth, with some types of mulch also exhibiting allelopathic properties (Liebl et al., 1992; Zimdahl, 1999). Straw mulch applied at planting has been shown to suppress weeds in potato, whereas straw applied after cultivation had less effect on weeds (Johnson et al., 2004). Straw mulch has effectively controlled grass and broadleaf weeds in tomato (Solanum lycopersicum), producing yields similar to treated with herbicides (Monks et al., 1997). Straw mulch at 6 t·ha−1 applied 4 weeks after planting increased tuber yield (Kar and Kumar, 2007), with low amounts (2.5–5 t·ha−1) of straw mulch not showing any effect on weed suppression and potato yield (Doring et al., 2005). Mulches reduce water evaporation from the soil and help maintain a stable soil temperature (Ji and Unger, 2001; Kar and Kumar, 2007; Lal, 1974). Mulching with rice (Oryza sativa) straw at 6 t·ha−1 narrowed down the daily soil temperature amplitude at 5-cm depth in sandy loam soil compared with a no-mulch treatment in Punjab, hence provided favorable hydrothermal regime for growth and development of potato (C.B. Singh, personal communication). Straw mulch also reduces tuber exposure to sunlight, which reduces tuber greening (Bellinder et al., 1996).
The objectives of this research were to determine effect of straw mulch at different rates applied alone or in combination with reduced rate of atrazine, atrazine at registered rate, and mechanical weed control on the suppression of weeds, and potato tuber weight and yield.
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