Seedbed preparation time and weeding intervals and their response on maize yield and traits in KP-Pakistan

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1 Basic Research Journal of Agricultural Science and Review ISSN Vol. 4(1) pp January 2015 Available online http// Copyright 2015 Basic Research Journal Full Length Research Paper Seedbed preparation time and weeding intervals and their response on maize yield and traits in KP-Pakistan Shahid Ali, Mohammad Akmal and Muhammad Afzal Faculty of Crop Production Sciences, the University of Agric. Peshawar *Corresponding author mail: Tel.: Accepted 23 December, 2014 Abstract Under uniform nutrients, irrigation and density, optimum timing of seedbed preparation and weeds control is highly important in tropics and subtropics for maximum productivity. The response of plowing time (dawn, noon and dusk) for seedbed preparation with appropriate weeding intervals (2, 4, 6 and 8 weeks) on maize (Zea mays L.) yield performance was observed at Agronomy Research Farm, the University of Agriculture Peshawar, Pakistan during summer Experiment was conducted in randomized complete block design, split plot arrangements in four replications. Plowing time was assigned as main plot and weeding interval as subplot treatments including a control as no weeding. Fertilizer was applied as single application during seedbed (N = 120 and P 2 O 5 = 50 kg ha -1 ) from Urea and Single Super Phosphate (SSP) sources. Results revealed higher (p<0.05) emergence in dawn and noon than dusk. Days to emergence, tasseling and silking did not differ, however, dawn plowed field delay maturity. Among the traits, ear length and grains weight were longer in dawn plowing field. Likewise, the tallest plant, with higher biomass, grain yield and harvest index was observed in dawn than noon. Weeding intervals affect (p<0.05) days to maturity. Weeding at 2 weeks interval showed the highest with maximum biomass and grain yield as compared to any other weeding intervals. Interaction was found significant for ear weight, plant height, weed biomass and total biomass per unit area. The study suggests that plowed field at dawn weeded preferably at 2 weeks interval showed healthy plants with traits to yield maximum production. Keywords: Time of plowing, time of weeding, yield traits, grain yield, maize cultivation INTRODUCTION Maize (Zea mays L.), the leading cultivated summer grain and fodder crop of Pakistan, ranks 3 rd after wheat and rice in cultivation under crop area allocated to it in rest of the world (Akmal et al., 2014). It is an equally popular cultivated crop in the cropping system of many countries of the world and South East Asia for grain and fodder production. A considerable biomass is consumed for the animal feed during winter due to severe cold and low production of other crops (Scott et al., 2012). Due to limited lifecycle of maize crop with multifarious industrial usage, it can be grown as spring and summer season crop in most of the sub-tropics (Asim et al., 2012). Maize is famous for corn s starch, corn s flakes, gluten, germ cake, lactic acid, alcohol, acetone and stalks as byproduct in paper and textile industry. Maize is popular in many countries for animal fodder making good quality silage and hay from stalk with and without cob for dairy bovines (Habib et al., 2011). Higher seasonal rainfall right after the crop cultivation delay weeding and affect yield adversely. The hot summer temperature of post

2 Shahid et al. 015 emergence of maize and sufficient moisture and nutrients encouraged weed growth which if nor eradicated in time will caused sever losses in yield and total biomass production per unit area. Maize is mostly planted on relatively huge acreages covering almost 40% of the total cropped area as summer leading crop starting from July after wheat harvesting in May. In central Asia, parts of Pakistan is also hit by seasonal moon-soon rains, which starts from July till mid-september contributing almost 70% total annual natural precipitation in the region. Right after maize cultivation, the rainy season starts which may delay in time weeding application to make free young seedling from overcrowding effects that are in competition with growth plants, adversely affecting crop growth and production (Asim et al., 2013). Contrary to the hot summer months (July onwards) exceeds rate of the evaporation from field crops under plenty sunshine for relatively longer photoperiods. Plowing fields in the month of July in hot summer days had shown a considerable soil evaporation of moisture from seedbeds that has been reported to 40% depending on existing field soil moisture and tools to be sued for planting (Akmal et al., 2010). Maize having a relatively larger seed size than any other grains cereals if the moisture from seedbed lost excessively at higher temperatures in tropics and subtropics during seedbed preparation and plowing tools used for the seedbed preparation might delay imbibition process and also adversely affect germinations and the desired density (Mahmood et al., 2012). Optimum soil moisture for a well-prepared seedbed is equally essential than soil moisture at the time of plowing and the technology used for planting. Area s where crop is grown on larger area on the cropping system and intensity of the solar radiation over the field is increasing at a relatively higher rate (Akmal et al., 2014). Time of panting can be manipulated to manage plowing and planting with minimum soil evapotranspiration. Water is and has remained a limiting factor for field crops in most of the regions for optimum production (Akmal et al., 2014). In an uneven plant stand optimum or desired production is impossible (Sarajuoghi et al., 2012). Optimum time for seedbed preparation has also contributed in yield differences through optimizing weed density per unit areas (Kolb et al., 2012). Keeping in view higher soil moisture losses during seedbed preparation by plowing in dawn and the subsequent effect of unexpected monsoon rainfall in the area, the study was designed to compare maize production and weed dry matter infestation, for grain yield and yield traits. MATERIALS AND METHODS To know the effect of plowing and weeding timings on maize production, the field experiment was conducted at Agronomy Research Farm, Agricultural University, Peshawar. Field remains long time under wheat and maize cropping system. Wheat (Triticum aestivum L.) was harvested in early May and about three weeks after the wheat harvest field was irrigated using flood irrigation system by stay 5.0 cm water depth on the field. A week after the flood irrigation, seedbed was prepared as per treatments requirements using tractor drawn cultivator. The experiment was designed in a randomized complete block, split plot arrangements and four replications. The plowing timings were assigned as main plots treatments and the weeding intervals as the subplots treatments with control as check. The main plots were plowed three times at dawn (4.0 noon (12.00) and dusk (8.00 p.m.) using cultivator runs twice with tractor followed by planking each time. Fertilizer was applied during seedbed preparation at a rate of 120 kg N ha -1 from urea and P 2 O 5 60 kg ha -1 from single super phosphate (SSP) source. Fertilizer was thoroughly mixed in soil by plowing during seedbed preparation. Main plots were sown with frill manually placing seeds at 0.75 m distance within rows spaced 0.20 m within rows using 33 kg ha -1 seeding rate. Eight rows were maintained for a subplot by leaving one blank row between subplot treatments as demarcations. Net size of a subplot was 6.0 m wide and 5 m long. Certified seeds of maize (cv. Kisan 90) were planted on June 10, A uniform plant density (66,000 ha -1 ) was maintained in all subplots about two weeks after emergence. The subplot treatment (weeding time) was manually performed to eradicate all weeds (broad and narrow leaves) at 2, 4, 6 and 8 weeks intervals. All plots were weeded accordingly during the growth period. The controlled treatment remained un-weeded for during the entire crop growth season. All the plots were uniformly treated with granules (Furadan) by placing 2-3 granules in the plant leaves for control of stem bother. Field was uniformly irrigated as per crop water demand four times during growth from emergence to harvesting. The data were recorded on days to emergence, emergence per unit area, days to tasseling, days to silking, and days to maturity by visual observation focusing four central rows in an experimental units when 50% plants in these central rows of an experimental unit were turned to the respective phases of development. Data on pant height and yield traits (i.e. ear weight, grain number and grains weight) were recorded on ten representative plants selected for the purpose at the time of physiological maturity on the harvest days from each experimental unit. Biological yield and grain yield (kg area -1 ) were recorded at two central rows in an experimental unit by manually harvesting all plants and subsequently converted into a standard unit (M g ha -1 ). Harvest index was estimated as ratio of grains yield to total biomass per unit area. All data were subjected to ANOVA technique as per appropriate model with SAS computer software and

3 016. Basic Res. J. Agric. Sci. Rev. Table. 1. Morphological features of maize as influenced by treatments plowing timings and weeding intervals. Treatments Emergence Days to (m -2) Emergence Tasseling Silking Maturity Time of plowings Dawn (4 a.m.) 10.2 a 6.0 a 44.4 a 51.1 a a Noon (12 noon) 9.2 ab 6.0 a 44.4 a 50.3 a b Dusk (8 p.m.) 8.3 b 6.0 a 44.4 a 50.3 a b Time of weeding Control 9.0 a 7.0 a 45.1 a 51.1 a b 2 weeks 9.6 a 6.0 a 44.4 a 50.2 a a 4 weeks 9.2 a 6.0 a 43.8 a 49.7 a b 6 weeks 9.3 a 6.3 a 44.2 a 49.7 a b 8 weeks 9.0 a 6.6 a 44.8 a 50.5 a a Interactions Plowing x Weeding NS NS NS NS NS Plowing (LSD) Weeding (LSD) = Timing of the plowing started with cultivator for seed bed preparation = Timing of manual weeding applications after completion of the 50% emergence NS = Non significantly different (P<0.05). Each value is mean of the replicated data means where found significant were categorized by values of the respective LSD (p<0.05). RESULTS AND DISCUSSION Data recorded on the establishment and growth phenology (days to emergence, days to silking, days to tasseling and maturity) of maize crop is shown in Table 1. Statistical results revealed that sowing time did influence 50% emergence. Dawn plowing showed a higher (p<0.05) emergence than dusk plowing. Plowing at noon and dusk did not show (p<0.05) any statistical difference in 50% emergence. Here it can be assumed that dusk than noon and dawn sowing permitted sufficient moisture to evaporate while plowing in a sunny day. The imbibition process of seed at higher post sowings temperature may also adversely affected the germination process. Contrary to that, noon and dawn treatments may have evaporated moisture relatively less than dawn with decreasing temperature of the day during post sowing that affected emergences significantly by the imposed treatments (Silva and Marcos, 1990; Egli and Rucker, 2012). Emergence is completion of imbibition and enzymes activation of a viable seed to germinate if otherwise the requirement is favorable. Longer the condition remained favorable, the process of germination starts and ends to germinate a healthy seedling. Nonetheless, completion phase of germination process may vary but not significantly (p<0.05). We have not observed any significant (p<0.05) changes in days to emergence, days to silking, days to tasseling and days to maturity for the applied treatments plowing time to maize crop. Contrary to this the weeding intervals showed uniform emergence. A variety with similar genetic makeup has to respond in emergence uniformly and the weeding treatments applied long after the completion of germination. Moreover, the same climate and agronomic practices under the given environment and soil nutrients status have not affected days to anthesis. However, marked differences observed in days to maturity. The two and eight weeks weeding intervals showed relatively early maturity conquered to four and six weeks including control treatments i.e. no weeding. It might be a coincidence, while days to maturity were recorded visually focusing the central rows in an experimental unit. Time to record an observation and rest of the full day growth activities may have made a significant change. Otherwise, there is no such reason to make a significant difference for 2 and 8 weeks weeding intervals over the 4 and 6 weeks in a similar environment (REF). Treatment interaction (weeding x plowing) did not show any significant (p<0.05) effect on growth stages of crop i.e. emergence, days to emergence, - silking, - tasseling and/or -maturity. Yield contributing traits i.e. ear length (cm), ear weight (g), grain number (ear -1 ) and thousand grains weight (g) is shown in Table 2. The data revealed that ear length was longer in plowing made at dawn as compared to noon- or dusk plowing. Ear length did not differ between plowing made at noon and dusk. The longest ear was observed for plots weeded at two weeks intervals, followed by 4, 6 and 8 weeks intervals. All three weeding intervals performed at 4, 6 and 8 week were nonsignificantly different (p<0.05) from each other. The lowest ear length was reported in control plot. Treatment interaction did not show any significant (p<0.05) effects on ear length. Ear weight was similar for dawn and noon, and noon and dusk plowings, but differed (p<0.05) between dawn and dusk (Table 2). Weeding interval

4 Shahid et al. 017 Table 2. Yield contributing traits (i.e. ear length & weight, grain number and weight) of maize as influenced by treatments plowing- and weeding time of applications to field. Treatments Ear length Ear weight Grain number Grains weight (cm) (g) (000 g -1 ) Time of plowings? Dawn (4 a.m.) 12.8 a 125 a a a Noon (12 noon) 10.9 b 124 ab a b Dusk (8 p.m.) 10.5 b 122 b a a Time of weeding? Control 10.3 c 121 c d d 2 weeks 12.0 a 127 a a a 4 weeks 11.5 b 124 b b b 6 weeks 11.1 b 123 b c c 8 weeks 11.2 b 123 b b cd Interactions Plowing xweeding NS * NS NS Plowing (LSD) Weeding (LSD) = Timing of the plowing started with cultivator for seed bed preparation = Timing of manual weeding applications after completion of the 50% emergence NS = Non significantly different (P<0.05). Each value is mean of the replicated data * = Significant at probability 5% using L Plant height (cm) Weed DM (g m -2 ) D a w n N o o n D u sk a b Biomass (M g ha -1 ) c d Harvet index (%) Grain yield (M g ha -1 ) e Weeding time after emergence (weeks) f Figure 1. Interactive effects of the treatments (weeding x plowing) on measured parameters are shown. Different window represents different parameters (a) plant height (cm), (b) weed dry matter (g m -2 ), (c) biomass (M g ha -1 ), (d) harvest index (%), (e) grain yield (M g ha -1 ), and (f) ear weight (g). Each value is mean of the replications. The vertical bars showing the LSD values (p<0.05) Ear weight (g)

5 018. Basic Res. J. Agric. Sci. Rev. showed a similar response on ear weight as explained for the ear length with highest for two weeks interval and lowest for the control plot with a non-significant difference for weeding made on 4, 6 and 8 weeks intervals. Grain number did not show any effect (p<0.05) by plowing time; however, it differed (p<0.05) by weeding intervals. The maximum grain number was observed for plot weeded at two weeks interval, followed by 4 and 8 weeks, which did not differ from each other. The six weeks intervals plots were next in grain number with lowest values for the control treatment. Grains weight was observed same (p<0.05) for dawn and dusk plowing but observed lower (p<0.05) for noon plowing treatment. The highest grain weight was observed for two weeks interval weeding, followed by 4 week interval weeding. The six weeks interval weeding did not differ from 8 weeks interval in grain weight data and likewise did by the eight weeks from control treatment. The only interactions (weeding x plowing) showed a significant (p<0.05) effect on ear weight (Figure 1f). The dawn plowed plot showed the highest ear weight in almost all weeding including the control plot. Similarly the dusk plowed plot was lower (p<0.05) in ear weight than dawn plowed, and may intercept with noon plowing occasionally. Control treatment did not differ (p<0.05) by plowing timings. However, weeding interval showed that noon and dusk plowed treatment did not vary at 4 weeks interval. Similarly, the six weeks weeding showed almost similar value at dawn and noon plowing. Yield traits are the basis of yield and production of maize crop (Asim et al., 2012). Ear length, weight, grain number and grain weight are the traits that finally contributed in yield. Difference in ear length significantly contributed in grain production. Changes in grain yield have a close association with grains yield. The healthier the grain traits or a particular trait is the better the yield. The smaller grains with higher number have not shown a significant effect on yield but heavier grains with healthy ears or longer ears have shown the maximum production. Data regarding plant height of maize (cm), weed dry matter (g m -2 ), biomass production, grain yield (M g ha -1 ) as well as harvest index (%) have shown a significant (p<0.05) effect under the treatments and their interactions (Table 3). The tallest plants were observed at dawn plowing, followed by noon plowing and the smallest in dusk plowing. Likewise, the tallest pants were observed at weeding made in 2 weeks intervals, followed by 4, 6 and 8 weeks with significantly (p<0.05) lower readings. Controlled plots (no weeding) showed the smallest plant height (cm). One can presumed that control over weeded plots faced competition for weeds with resources e.g. light, water and nutrients including available space per unit ground area and hence might have resulted relatively stunted unhealthy plant (Gomez et al., 2012). A similar response was observed for treatments weeding intervals. The delayed weeding interval from 2 to 8 weeks subsequently decreased (p<0.05) height showing that early weeded (2 weeks interval) relaxed plants from high competition for the available resources. As weeding interval delayed from 2 to 4 and from 4 to 8 weeks, plant suffered with resource scarcity during growth for adversely affect the height and biomass (Cerrudo et al., 2012). It is known that stem elongation is in response to rate of meristematic cell production rate (Akmal and Hirasawa, 2004). The more optimum the water and nutrients available to crop the faster would be the rate of cell production and growth. A two weeks delay in weeding may have brought young plants in stress for water, light and nutrients which resulted in poor growth and a significant difference in height and biomass (Cerrudo et al., 2012). Interactive effects of treatments (weeding x plowing) were also found significant (p<0.05) for plant height (Figure 1a). When compared with noon and dusk plowing, the dawn plowing resulted tallest plant in control as well as in any given weeding intervals. Likewise, dusk plowing showed the lowest height for all weeding intervals including control. The dawn plowing was tallest in height followed by noon and dusk treatment with similar values to dawn at 4 week weeding and dusk at 6 and 8 weeks interval weeding. Dawn plowing might have retained enough moisture by less evaporation loss at a relatively low temperature of the days which has resulted early imbibition and rapid emergence. Early emergence therefore may have resulted in significantly taller plants over the late emerged at either noon or dusk plowed treatments. Here one could also add that long hourly low temperature at nights followed by dawn may have contributed to soil moisture. Contrary to that, the noon at high temperature and the dusk followed by high temperature of the day was unable to compensate soil evaporation loss made during plowing for seedbed preparation. Significantly lower weed dry matters (DM g m -2 ) were reported at dawn, followed by noon and the highest at dusk plowing. The highest DM of weeds was also observed in controlled plots not weeded, followed by a significant decrease at 2, 4, 6 and 8 weeks intervals. Only 2 and 4 weeks weeding intervals did not differ (p<0.05) from each other for weed dry matter. The interactive effect of treatments (weeding x plowing) was significantly different for weed DM (Figure 1b). When compared with dawn and noon plowing, the dusk plowing showed the highest weed DM at control and every weeding interval given to the maize crop. Likewise, dawn plowing showed the lowest weed DM at all weeding treatments. Noon plowing was mostly in between dawn and dusk with a closer value to dawn at 2, 6 and 8 weeks intervals. It is quite natural that no weeded plot yields higher biomass. However, the lower weed biomass at 2 and 4 than 6 and 8 weeks interval treatment is also logical. Plant growth is sigmoidal, and it increased at a relatively higher rate when plants enter in linear phase of development. The reason for that acceleration in growth in the later stage of development is more associated with fraction of stem

6 Shahid et al. 019 Table 3. Plant height, biomass production, grain yield and harvest index of maize as influenced by treatments plowing- and weeding time of applications to field. Treatments Height Weeds Biomass Grain yield H.I. (cm) (g m -2 ) (M g ha -1 ) (Mg ha -1 ) (%) Time of plowings Dawn (4 a.m.) a c a 2.75 a a Noon (12 noon) b b b 2.52 a b Dusk (8 p.m.) c a c 2.11 b b Time of weeding Control 156.1e a e 1.84 d c 2 weeks a b a 2.99 a c 4 weeks b b b 2.76 b b 6 weeks c c c 2.37 c b 8 weeks d d d 2.34 b a Interactions Plowing xweeding * * * NS NS Plowing (LSD) Weeding (LSD) = Timing of the plowing started with cultivator for seed bed preparation = Timing of manual weeding applications after completion of the 50% emergence NS = Non significantly different (P<0.05). Each value is mean of the replicated data * = Significant at probability 5% using LSD contribution in the total dry matter. The 6 and 8 weeks interval weeded treatments have higher stem fraction than the 2 and 4 weeks interval weeding treatments and hence shown a higher weed dry matter. As explained earlier, dawn plowing might have contributed less in moisture loss than noon and dusk and hence extends higher weed biomass. Generally, weeds can survive better than cultivated crops in poor nutrients, water and harsh environment (Malik et al., 2012). Dry matter and grains yield (M g ha -1 ) also affected by plowing time and weeding intervals (Table 3). The biomass production was observed highest in dawn plowing, followed by noon and lowest (p<0.05) in dusk plowing. Biomass production also showed significant responses when crop weeded at different intervals. The highest biomass was recorded for plots weeded at 2 weeks intervals, followed by 4, 6 and 8 weeks. Lowest biomass was observed in control i.e. no weeded. Treatment interactions (plowing x weeding) showed marked (p<0.05) differences in biomass. Two weeks intervals in dawn plowed showed the maximum biomass. Irrespective of control plots, dawn plowing exceeded in biomass than rest of the two treatments e.g. noon and dusk plowings at all weeding intervals starting from 2 to 8 week intervals. Similarly, noon plowing remained higher in biomass production than dusk plowing at almost all weeding but eight weeks. Taller plants with healthy initial status at dawn over noon or dusk from emergence were the major reasons of higher biomass (Martin et al., 2012). Grains yield (M g ha -1 ) did not differ at dawn and noon but remained statistically higher from dusk plowing. The control treatment showed the lowest grains yield at any weeding interval treatment. Two weeks interval showed the highest grains yield which significantly declined when weeding intervals delayed from 2 to 8 week. The interactions did show any significant effect in grains yield with highest for dawn and lowest for dusk plowing at any weeding intervals including control. Dawn plowing at noon with 6 weeks weeding did not differ in grains yield from control. The higher biomass and grain yield at dawn is no doubt associated with post plowing environment over the field. Dawn plowed field was probably least evaporated in cooler temperature of the day. Contrary to that, noon plowed was highly expose to sun rays with hot air during seedbed preparation, but the dusk treatment was not only exposed to day light for about 16 h but also exposed to hot dry air current when start plowing the field and hence has caused relatively higher water loss which significantly loss in biomass and grains yield. Early weeding has relaxed plants from competition for nutrients, water, space and light etc. resulting higher grain and biomass. Harvest indices were influenced by plowing and weeding treatments, dawn plowed showed the highest harvest index as compared to rest of the noon and dusk plowings. Similarly, weeding application after 8 weeks showed the highest harvest index, followed by a significant decrease for 6 and 4 weeks with a nonsignificant (p<0.05) difference from each other. The two weeks weeding interval and control did not show any change for harvest index, but found lower than 6 and 8 weeks interval treatment. Interactions (weeding x plowing) did not show any profound differences in harvest indices. The higher harvest index of early weeded was reason of better growth and higher biomass and grain yield. Improvement in harvest index means yield improvement particularly the grain ratio to total biomass.

7 020. Basic Res. J. Agric. Sci. Rev. Dawn plowing over noon- or dusk plowing showed significantly positive response on yield traits and subsequently the yield. The larger maize grain required considerable moisture to start germination process in time. Plowing field in hot summer days in area, like Peshawar, causes excessive soil moisture depletion that adversely affects germination and plant stand. Moreover, in time weeding for stand establishment relaxed young plants from stress of production factors i.e. light, space, nutrients and moisture etc.. Contrary to this, delay in weeding encouraged weed establishment, which adversely affected plants growth resulting unhealthy plants with poor traits. CONCLUSION The study suggests that early plowing at relatively cool hour of the day accelerated the process of germination and optimum stand per nit area. Moreover, early weeding allows seedlings to take maximum advantage of the resources i.e. water, nutrients and light for maximum production. It is therefore recommended to start seedbed preparation as early as possible to avoid un-necessary evaporation for cops like maize having larger seeds and sensitive to soil moisture. Acknowledgement The authors acknowledged with thanks from the core of heart to Prof. Dr. D. H. Putnam, PES, UC Davis for stay in his lab and used the computer with SAS software facilities for data analysis and paper drafting. Equal thanks are extended for the Department of Agronomy, to provide field and supporting staff facilities for the research work. REFERENCES Agric. Statistics. (2011). A handbook of agricultural statistics. Ministry of Food, Agricultural, and Livestock. Government of Pakistan, Islamabad. Akmal M, Asim M, Afzal M, Gilbert M (2014). Influence of seasonal variation on radiation use efficiency and crop growth of maize planted at various densities and nitrogen rates. Pak. J. Agri. Sci. 51: Akmal M, Hameed-ur-Rehman, Farhatuallah, Asim M, Akbar H (2010). Response of maize varieties to nitrogen application for leaf area profile, crop growth and yield components. Pak. J. Bot. 42(3): Akmal M, Shah A, Zaman R, Afzal M, Noor ul A (2014). Carryover response of tillage depth, legume residue and nitrogen-rates on maize yield and yield contributing traits. Intl. J. Agric. Bio. Under Review with Ref Asim M, Akmal M, Khan A, Farhatullah R (2012). Rate of nitrogen application influences yield of maize at low and high populations in Khyber Pakhtunkhuwa, Pakistan. Pak. J. Bot. 44: Asim M, Akmal M, Khattak RA (2012). Maize response to yield and yield traits with different nitrogen and density under the climate variability. J. Plant Nutrition. 35: Cerrudo D, Page ER, Tollenaar M, Stewart G, Swanton CJ (2012). Mechanisms of yield loss in maize caused by weed competition. Weed Sci. 60: Egli DB, Rucker M (2012). Seed vigor and the uniformity of emergence of corn seedlings. Crop Sci. 52: Gómez R, Liebman M, Sundberg DN, Chase CA (2012). Comparison of crop management strategies involving crop genotype and weed management practices in conventional and more diverse cropping systems. Renewable Agric. Food Systems. DOI: /S Habib G, Hassan MF, Akmal M, Ahmad S, Ghufranuallah (2011). Maize response in cereal based rotation with legume as catch crop. Pak. J. Bot. 43: Kolb LN, Gallandt ER, Mallory EB (2012). Impact of spring wheat planting density, row spacing, and mechanical weed control on yield, grain protein, and economic return in Maine. Weed Science. 60: Mahmood S, Abid R, Yasin G, Arif H, Irshad A (2012). Growth and yield parameters as potential indicators of selection for moisture deficit tolerance in some Pakistani wheat (Triticum aestivum L.) cultivars. African J. Agric. Res. 7: Malik MI, Mahmood S, Yasin G, Bashir N (2012). Oxalis corniculata as a successful lawn weed: a study of morphological variation from contrasting habitats. Pak. J. Bot. 44: Martin K, Raun W, Solie J (2012). By-plant prediction of corn grain yield using optical sensor reading and measured plant height. J. Plant Nutrition. 35: Sarajuoghi M, Mafakheri S, Rostami R, Shahbazi M (2012). Rapeseed residue management for weed control and corn production. Indian J. Sci. Technology. 5: Scott MP, Byrnes K, Blanco M (2012). Dry matter and relative sugar yield from enzymatic hydrolysis of maize whole plants and cobs. Plant Breeding. 131: Silva WR, Marcos FJ (1990). Evaluation of imbibition and initial development of maize seed embryo structures subjected to different water potentials. Anais da Escola superior de Agricultura Luiz de Querioz. 47: