Soil Solarization: An Organic Weed-Management Approach in Cauliflower

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Soil Solarization: An Organic Weed-Management Approach in CauliflowerMuhammad Azim Khan a , Khan Bahadar Marwat a , Anees Amin a ,Anwar Nawaz a , Rahamdad Khan a , Haroon Khan a & Hamid UllahShah ba Department of Weed Science, KPK Agricultural University,Peshawar, Pakistanb Department of Agricultural Chemistry, KPK Agricultural University,Peshawar, Pakistan

Accepted author version posted online: 20 Jun 2012. Version ofrecord first published: 27 Jun 2012

To cite this article: Muhammad Azim Khan, Khan Bahadar Marwat, Anees Amin, Anwar Nawaz,Rahamdad Khan, Haroon Khan & Hamid Ullah Shah (2012): Soil Solarization: An Organic Weed-Management Approach in Cauliflower, Communications in Soil Science and Plant Analysis, 43:13,1847-1860

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Communications in Soil Science and Plant Analysis, 43:1847–1860, 2012Copyright © Taylor & Francis Group, LLCISSN: 0010-3624 print / 1532-2416 onlineDOI: 10.1080/00103624.2012.684822

Soil Solarization: An Organic Weed-ManagementApproach in Cauliflower

MUHAMMAD AZIM KHAN,1 KHAN BAHADAR MARWAT,1

ANEES AMIN,1 ANWAR NAWAZ,1 RAHAMDAD KHAN,1

HAROON KHAN,1 AND HAMID ULLAH SHAH2

1Department of Weed Science, KPK Agricultural University, Peshawar, Pakistan2Department of Agricultural Chemistry, KPK Agricultural University, Peshawar,Pakistan

Studies were conducted at KPK Agricultural University, Peshawar, Pakistan, in June2008 and 2009 using a randomized complete block design. Plots were covered withtransparent polyethylene films for different periods (0, 2, 4, 6, 8, and 10 weeks). Thetemperature inside the film was about 10 ◦C greater than the atmospheric temper-ature. Solarization increased nitrogen (N) and organic-matter levels in both years,probably because of decomposition of plant residues. Increasing the period of solar-ization decreased weed density and both fresh and dry biomass. The effectivenessof solarization was species specific. In 2008, Cirsium arvense L. was controlled inthe solarized soil, whereas Vicia sativa germination was stimulated by solarization.In 2009, suppressed weeds included Sorghum halepense whereas Chenopodium albumL., Cyperus rotundus, and Rumex crispus L. were unaffected. Solarization increasedyield of cauliflower (Brassica oleracea L.) in both years. These results suggest thatsolarization should be practiced before planting horticultural crops in areas with a hotclimate.

Keywords Cauliflower, nursery, soil heating, soil nutrients, solarization, vegetable,weeds

Introduction

The presence of weeds reduces the growth of a wide range of commercially grown crops(Khan et al. 2003). Thus, worldwide, a 10% loss of agricultural production can be attributedto the competitive effect of weeds (Moody 1991). In spite of using different weed-controlmethods and application of the latest technology, weeds are still a problem in crop pro-duction. There are problems such as herbicide resistance, weed shift, and threats to theenvironment and biodiversity associated with the use of herbicide. Worldwide, there is anincreasing interest in integrated control measures and combinations of different methodsto reduce the use of chemical pesticides (Bennett, Leifert, and Whipps 2006). In the futurethere will be increasing pressure to reduce pesticide inputs in agricultural systems for envi-ronmental reasons (Mortensen, Bastiaans, and Sattin 2000), and this will require researchon the development of more sustainable weed-control strategies (Batlla and Arnold 2007).

Received 22 February 2010; accepted 5 July 2011.Address correspondence to Muhammad Azim Khan, Department of Weed Science, KPK

Agricultural University, Peshawar 25130, Pakistan. E-mail: [email protected]

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1848 M. A. Khan et al.

Around the globe approximately 3 million people are adversely affected and200,000 die each year from pesticide poisoning. A majority of them are in developingcountries (World Health Organization 1990). In Pakistan, herbicide use in crops is increas-ing; however, no herbicide is available in the market that is registered for use in nurserycrops. The use of herbicides in vegetables further create problems. At present, more than108 types of insecticides, 30 types of fungicides, 39 types of herbicides, five types ofacaricides, and six different types of rodenticides are being used in Pakistan (PPSGDP2002), and the import of pesticides is increasing gradually every year (Economic Surveyof Pakistan 2006). The use of pesticides in Pakistan has increased by 1169% in the past20 years, which is an alarming situation as far as human health is concerned (Anonymous2000). Effects of pesticides have been reported in milk, feed, cottonseed, fruits, vegetables,and fishmeal throughout the country (Saqib et al. 2005). Thus, this deteriorating situationregarding the use of pesticides warrants a shift to other methods of weed control that areeffective and environmentally friendly. Cauliflower has one of the highest pesticide loads(ranking 21 out of 45 common fruits and vegetables studied in 2006 by the EnvironmentalWorking Group) and is therefore a prime candidate for switching to organic management(http://www.foodnews.org/).

As global concerns regarding environmental quality grow along with the human pop-ulation in the 21st century, concepts such as solarization and other uses of solar energy inagriculture will likely become increasingly important (Stapleton 2000). During the solar-ization period, 85–95% of radiation from sunlight penetrates the clear mulch and heats thesoil (Lamont 2005). Ham, Kluitenberg, and Lamont (1993) reported that soil temperaturesaveraged 6 ◦C greater under clear polyethylene mulch than in uncovered seedbeds, depend-ing on depth in the soil profile. Haidar et al. (1999) reported that all solarization treatmentssignificantly reduced the seed germination of dodder seeds at 0 cm deep in comparisonto nonsolarized controls. Under field conditions, seed aging of weeds is also acceleratedthrough the soil solarization, which is a physical technique used for weed and plant diseasecontrol in regions receiving high levels of solar radiation (El-Keblawy 2003). It is theorizedthat solarization controls weeds in the following ways: (1) direct thermal killing of propag-ules, (2) high temperatures interact with toxic volatiles from decaying organic matter toweaken weed propagules so they are predisposed to microbial infection, and (3) breakingpropagule dormancy followed by scorching of trapped weeds (Rubin and Benjamin 1984).

Despite inconsistent efficacy, soil solarization is considered a viable option for pestcontrol in organic cropping systems and has been implemented in the transition from con-ventional crop production to organic crop production in Florida (Winsberg et al. 1998).In general terms, annual weeds are more effectively controlled than perennial weeds bysolarization (Chase et al. 1998; Stevens et al. 1990). However, several studies have shownthat perennial weeds can also be controlled by solarization.

In Pakistan, there is high risk of herbicide exposure because of its extensive use indifferent crops. There is plenty of sunlight, with temperature goes up to 50 ◦C in summer.Soil solarization could provide nonchemical, organic weed control. The present studieswere conducted to investigate the effects of solarization periods on cauliflower, weeds, andsoil nutrients status in Peshawar, Pakistan, to decrease the risk of herbicide exposure andproduce vegetables organically.

Materials and Methods

Field experiments were conducted during June 2008 and June 2009 at the AgriculturalResearch Farm, Khyber Pukhtunkhwa Agricultural University, Peshawar, Pakistan, to eval-uate the effects of soil solarization periods on soil nutrients status, weeds, and yield of

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Soil Solarization for Weed Control 1849

cauliflower (Brassica oleracea L.). The fields used were in a safe place, away from heavyfoot traffic. Before solarization, the experimental area was cultivated with maize in sum-mer and wheat in winter in both years, and soil showed a high infestation of differentsummer and winter weeds. Then the soil was raked (to remove plant debris and rootfragments). The field was plowed three times and then leveled with a soil leveler. Thismade the fields free of weeds, debris, and large clods, which could raise the plastic offthe ground. After leveling, the field was irrigated up to field capacity using flood irrigationboth years.

Soil samples from the upper 10 cm of the soil were collected before and after solar-ization from each treatment during both the years for chemical analysis. Soil temperaturewas measured at 10 cm deep because the germination of weed seeds is concentrated inthe upper layers of soil. Air temperature was also recorded at 1 m above the soil surface.The experiment was laid out in a randomized complete block design. Polyethylene films(75 µm thick) were used in such a way that there were six treatments (solarization peri-ods of 2, 4, 6, 8, and 10 weeks). No solarization (control) was included for comparison.The size of each subplot was 3 × 4 m in both years. Experimental units were covered withpolythene films as per design, and the edges of the films were buried in the soil to avoidgaseous exchange. Films were placed in such a way that there were no air packets withminimum space between soil and polythene films. Soil temperature data of the treatmentswere recorded around 1–2 pm midday on weekly intervals using a thermometer (TP 3001,China) at a soil depth of 10 cm. In summer, sunset occurs at 7 pm and sunrise is at 5 am.The thermometer was inserted into the films and temperature was measured. The holeswere then closed with squash tape. Polyethylene films were removed from the treatmentsat 2-weeks interval as per the design. After solarization, the experimental units were indi-vidually plowed manually, with the soil disturbance not more than 10 cm deep. In October2008 and 2009, cauliflower variety Burid Sport China was transplanted. No fertilizers wereapplied during the course of the 2 years.

To record weed-related parameters, quadrates of 50 × 50 cm were placed randomly atfive places in each treatment, and the weeds inside were identified and counted.

Statistical Analysis

The data recorded individually for each parameter were subjected to the analysis ofvariance (ANOVA) technique, and significant means were separated utilizing the leastsignificant difference (LSD) test (Steel and Torrie 1980).

Results and Discussion

Soil Temperature

Solarization increased the soil temperature up to 52 ◦C as compared 42 ◦C in nonsolarizedtreatments at 10 cm deep in the last quarter of June both years. Thus temperature belowthe film was almost 10 ◦C greater than the nonsolarized soil (Figure 1). Data showed thatsoil temperature in solarized treatments was comparatively higher (>45 ◦C) until the firstweek of August and then gradually decreased. We could not follow the data-recordingschedule strictly because of cloudy weather at noon twice a week. Usually monsoon rainsoccur in July, which can disturb the film. Therefore, soil temperature data were recordedonly on sunny days. In June, weather is usually clear, hot, and dry and therefore there isenough time for the farmers to solarize the soil before monsoon rains. Overall temperaturein 2008 was greater than in 2009.

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Dates

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Figure 1. Effect of solarization on soil temperature (color figure available online).

Soil Nitrogen Content (%)

In addition to direct physical effect of soil solarization on the soil temperature, chemicalchanges in soil composition were also observed. One of the most striking chemical changeswas noted for the increased concentration of nitrogen (N) in solarized plots. Overall N con-tent increased with increasing solarization period in both years. The lowest concentrationwas recorded in control plots. However, solarization increased N content up to 6 weeks inyear 1 and 8 weeks in year 2 and then remained constant. In the longer solarization period,more chemical decomposition occurred, which might have increased the N content. Datarevealed that solarization, whether for short or long period of time, increased the N contentas compared to control during both years (Figure 2). This increase in N was very small,however; consistent solarization for several years might be more effective in increasing thetotal N content. Other minerals (phosphorus, potassium), electrical conductivity, and pHwere also studied, but solarization did not have a significant effect on these for either year;therefore, the data was not included in this article.

Soil Organic Matter (%)

Soil organic matter plays an important role in crop production. Organic-matter content ofsoil increased with soil solarization period. The obtained results underline that soil solariza-tion even for 2 weeks increased organic matter, but longer periods of solarization constantly

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Figure 2. Effect of solarization on soil nitrogen content.

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and slightly increased the soil organic matter during both years (Figure 3) as compared tothe control (nonsolarized soil). Soil of the experimental site is deficient in organic mat-ter, as indicated by the control plots, and therefore consistent practice of solarization cangreatly increase the organic-matter content of the soil. The same trend was observed duringboth years.

Weed Biomass

In the solarization process, chemical and biological processes occur that are due to hightemperature and humidity, which ultimately affect weed seeds and propagules. Effect ofsolarization periods on fresh weed biomass was significant during both years (Figure 4).Weed biomass decreased with solarization period as compared to the control plots.Statistically minimum and comparable fresh weed biomass were obtained in plots solar-ized for 4, 6, 8, and 10 weeks during both years. However, the change in dry weed biomassis very small as compared to change in fresh weed biomass (Figure 5). This might be dueto the species-specific effect of solarization on weed as water content of different weedspecies is always different because the decrease in dry-matter accumulation is very small.With the increasing solarization period, fresh as well as dry weed biomass was decreasedduring both years. Maximum fresh and dry weed biomass was recorded in the controlplots. Interestingly the weed density in solarized plots was less than in the control, but thevegetative growth of weeds in the solarized plot was luxuriant green and grew faster ascompared to weeds in the control. This might be due to more N and organic matter in the

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solarized plots. Response of fresh and dry weed biomass to solarization was similar duringboth years.

Weed Density (m−2)

Major weed species recorded in the experimental plots in year 1 were Anagallis arvensis L.,Poa annua L., Coronopus didymus L., Melilotus perviflora, Vicia sativa L., Ammi-visnagaL., and Cirsium arvense L. (Table 1), and in year 2, the major weeds in the experimen-tal field were A. arvensis, Chenopodium album L., Fumaria indica, P. annua, Rumexcrispus L., Sorghum halepense L., Ammi-visnaga L., Convolvulus arvensis L., Cyperusrotundus L., Euphorbia helioscopia L., Medicago denticulate L., and Silybum marianumL. (Table 2). It was noted that with the increasing period of solarization, the total densityof all weed species decreased except for Vicia sativa in year 1 and C. album in year 2,which showed stimulatory and zero response, respectively, to solarization (Tables 1 and 2).Comparing the weed density in the control with the solarization, the density of all thespecies decreased during both years. However, different species showed different responsesto the solarization period. Interestingly, C. arvense was totally controlled by the solar-ization as no C. arvense was observed in the solarized plot as compared to nonsolarized

Table 1Weed species recorded in the experimental plots during 2008

Weed species

Solarizationperiod

Anagallisarvensis

Poaannua

Coronopisdidymus

Melilotusperviflora

Viciasativa

Ammivisnaga

Circiumarvensis Mean

Control 64.25 19.87 a 30.75 a 7.12 3.00 14.00 a 5.00 20.532 weeks 51.37 8.12 b 6.25 b 4.37 3.37 2.37 b 0.00 10.354 weeks 43.87 5.62 b 9.50 b 6.37 4.25 2.12 b 0.00 10.246 weeks 34.37 4.25 b 6.25 b 5.25 5.25 2.37 b 0.00 8.248 weeks 43.00 8.00 b 8.50 b 5.50 7.25 3.37 b 0.00 10.7110 weeks 32.00 3.75 b 5.62 b 2.62 7.00 3.87 b 0.00 7.83Mean 44.81 8.26 11.14 5.20 5.02 4.68 0.83

Note. Means data showing different letters are significantly different from each other. Significancelevel is 5%.

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soil in year 1. In year 2, S. halepense was effectively suppressed by solarization. Mosttroublesome weeds of the experimental areas (P. annua, C. arvense, and S. halepense)were effectively controlled. As P. annua is a serious threat to winter nurseries and veg-etables, solarization is a fair option of weed control for the farmers in hot climates in thesummer. Almost all the herbicides have shown weak responses against P. annau, furthersupporting the benefits of solarization.

Yield of Cauliflower

Figure 6 indicated that yield of cauliflower was significantly affected by soil solarizationduring both years (2008 and 2009). Maximum cauliflower yield was obtained from plotssolarized for 2 weeks or more during year 1. During year 2 yield of cauliflower increasedwith the increasing period of solarization. Solarization for more than 8 weeks had no effecton the cauliflower yield. With the increasing solarization period, flower yield of cauliflowerincreased. In control plots, the flowers of cauliflower were reduced and unattractive tocustomers.

Discussion

Temperature

Cloudbursts usually start from mid-July in the study area, and therefore early solarizationstarting from the first week of June might be effective in increasing the soil temperature.Days are longer in June and July and thus sunlight could be trapped for extended peri-ods of time. Starting solarization late might not be effective because of monsoons, cloudyweather, shorter days, and low atmospheric temperature. It was observed that atmospherictemperature was greater during year 1, which can influence the success of solarization.Monsoon not only tore the plastic films but also may cause water and wind erosion andweed seed dispersal. Cloud cover, cool air temperatures, and precipitation events duringthe treatment period will reduce solarization efficiency (Chellemi et al. 1997). The fieldshould be covered with the used polyethylene films until the planting season of subsequent

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Figure 6. Effect of soil solarization on cauliflower yield (kg ha−1).

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vegetables. Many farmers in the region do not have a fence around their fields; therefore,wild animals and dogs may puncture the plastic films, as noted in our experiment. Smallholes in the films may cause moisture loss and gaseous exchange from the soil, whichmight adversely affect the solarization process. Hence, it could be concluded from thepresent study that solarization should be practiced on a small scale and protected from ani-mals. We measured temperature in the upper 10 cm as greater temperatures were recordednear the soil surface and then decreased with increasing soil depth. Atmospheric tempera-ture in the study area sometimes reached 50 ◦C. As a majority of the farmers in Pakistan arenot well educated, soil solarization provides a simple and easy opportunity to prevent weedinfestation. Disposal of the used plastic is a problem. However, biodegradable plastic filmscould give an interesting advantage (Castronuovo et al. 2005). Biodegradable films degradeprogressively during solarization and they do not release toxic residues in the environment(Scopa et al. 2008).

Nitrogen Content

Overall, soil N content was increased by solarization during both years. This might bedue to the presence of plant materials buried in the soil. A greater level of mineral N inthe soil solution eventually originates from enhancement decomposition of soil organicmatter and biomass (Chen et al. 1991). Solarization periods significantly affected the soilN content during both years. Soil disinfestations are known to affect the soil properties andcontent of mineral nutrients (Chen et al. 1991). In most soil, electrical conductivity andlevels of nitrate (NO3), ammonium (NH4), potassium, calcium, magnesium, and sodiumwere greater after solarization (Ahmad, Hameed, and Aslam 1996). Solarization for a shortperiod of time (2 weeks) also increased N content but longer periods of solarization weremore effective in increasing N content. This increase is due to the decomposition of theprevious crop and residues and young germinated weeds at higher temperatures insidethe plastic film. Extended periods of solarization increased the N content in year 1 moresharply than in year 2. This might be because temperature during year 1 was greater thanyear 2. However, the trend was the same during both years. As previous studies show(Chen et al. 1991; Patricio et al. 2006) the increase in ammonium (NH+

4)-N is usuallygreater with high amount of organic matter, because temperature enhancement increasesorganic N mineralization. Increases in available mineral nutrients in soil can play a majorrole in the effect of solarization, leading to increased plant health and growth and reducedfertilization requirements (Stapleton 2000).

Soil Organic Matter (%)

Organic matter is the life of the soil; however, Pakistani soil is deficient in organic-mattercontent. As shown in the control plots, organic-matter content of the experimental siterepresenting the farmers’ field was left then 1%. Thus, there is a hope to use solariza-tion as a technique to increase the soil organic matter, especially in small fields that willbe used for nursery growing, which will ultimately increase the crop yield and quality.Gasoni et al. (2008) reported that organic-matter content in the solarized soil was greaterthan in nonsolarized soil. The trend of the organic matter was the same in both years,however; the sharp line of organic-matter content in year 1 is probably due to highertemperature.

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Weed Biomass (g m−2)

During both years, soil solarization greatly decreased fresh and dry weed biomass ascompared to the control. It was observed that many annual as well as noxious perennialweeds (Sorghum halepense and Cirsium arvense) were greatly controlled by solarization.However, it is yet to be confirmed that either seed or vegetative parts of the weeds werekilled by solarization. Interestingly, there was less weed density and luxuriant growth ofweeds in solarized treatments, probably because of the availability of N and other min-erals in the soil, due to the solarization process. The responses of fresh and dry weedbiomass to solarization were similar during both years. However, year 1 was comparativelywarmer than year 2, which ultimately increased the nutrient levels in the soil, subsequentlysupporting weed growth. Many weed seeds are heat sensible and thus are killed by hightemperature, as temperature as high as 54 ◦C was recorded during June 2008. The solar-ization process also determines a favorable effect on crop productivity because of greatermineralization and increases N availability in the short run (Scopa et al. 2008). Thus greatermineralization and N availability not only give advantage to the crop plants but also favorgermination of the heat-resistant weeds, which use available resources.

Weed Density (m−2)

Differential response of weed species to solarization has been reported earlier. Studiesshow that monocot weeds were not controlled by solarization (Tamietti and Valentino2000). While in our experiment, P. annua in year 1 and S. halepense in year 2, bothtroublesome weeds of the area, were successfully controlled to a great extent. Broadleafweeds were also controlled effectively, including a perennial, C. arvense, as this weeddid not appear in the solarized plots. However, we are not sure whether vegetative partsor seeds were killed by the solarization as the area was previously infested with theseperennial weeds. Our results are in contrast to the results that show soil solarization withpolyethylene was effective in eradicating all the annual weeds but not the perennial weedC. arvensis (Triki, Priou, and El-Mahjoub 2001).

All broadleaf and grassy weeds recorded in the experiment are threatening the veg-etable production in the region, and thus success of solarization will prove a baseline forweed control in vegetables. As herbicide application is not common in vegetable produc-tion, the farmers have no choice, especially when rainy season starts in February/March.Solarization reduced the population of many weeds, including P. annua (Benlioglu et al.2005). Furthermore, Elmore (1991) indicated that Melilotus was not controlled by soilsolarization. The suppressive effect of the opacity of the solarization mulch on weed emer-gence also varied among weed types (Hasing, Motsenbocker, and Monlezun 2004), andclear film consistently showed longer periods of sustained high temperatures, increasedlettuce yield by enhancing plant growth and head weight, and reduced weed densities,especially from grasses. Seeds in the upper layer of the soil (2.5 cm) deteriorated more ascompared with those buried at 7.5 and 15 cm deep (El-Keblawy and Al-Hamadi 2009).The greatest temperatures during solarization are achieved at or near the soil surface, andsoil temperature decreases with the increasing depth (Stapleton 2000). Thus it seems thatsoil solarization could prove effective for killing weed seeds, especially in no-tillage orzero-tillage systems. In no-till systems, the seeds accumulate at the soil surface because oflack of soil disturbance (Hoffman, Owen, and Buhler 1998), and species that can germinatefrom shallow depths or from within the surface residue layer can be easily targeted (Barberiand Lo-Cascio 2001). In contrast, tillage systems disperse seeds deep down the tillage

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profile (Clements et al. 1996) and tend to favor species that require soil disturbance. Thetop 5 cm of soil contained 90%, 61%, 37%, and 33% of the seeds under no-till, chisel plow,moldboard plow, and ridge tillage systems, respectively (Swanton and Shrestha 2008).Weed species’ composition and depth of weed propagule placement further influence soilsolarization efficacy (Chase, Sinclair, and Locascio 1999). Although zero-tillage conceptsare not that popular in Pakistan, there are chances of using this method for weed control ona small scale for cash crops and vegetable nurseries. Nurseries are usually grown in smallno-tillage areas in Pakistan, and solarization may be successful in these situations.

Cauliflower Yield

Cauliflower is an important winter vegetable in Pakistan and is used all over the coun-try. Because cauliflower is marketed in Pakistan by weight, the increased weight resultingfrom the solarization period has a direct short-term economic impact on the farmer’s netincome. The cauliflower yield during year 1 (2008) was greater than in year 2 (2009) prob-ably because of the greater temperature in year 1. In year 1, solarization for a short periodof time (2 weeks) was effective in increasing the soil nutrient status, decreasing the weedbiomass, and increasing the cauliflower yield. In year 2, the temperature was low, whichpositively affected the weeds. This difference in trend might be attributed to the greatertemperature during year 1, which killed the weed seeds in just 2 weeks of solarization.In year 2, the maximum yield was observed when the soil was solarized for 8 weeks.Hasing, Motsenbocker, and Monlezun (2004) reported that clear film solarization increasedlettuce yield by enhancing plant growth and head weight and reduced weed densities,especially that of grasses.

In Pakistan, labor is cheaper and readily available year-round. However, weeding isunfeasible in many nursery and vegetable crops because of physical injury to the cropseedlings. Thus, hand or other mechanical weeding is not practical in nurseries and forsome vegetables, and chemical weed control is hazardous to health and environment. Thisleaves soil solarization as the only feasible and economically viable method of weed con-trol for nurseries in Pakistan. Labor charges (Rs. 200 = US$ 2.30 day−1) and polyethylenefilm prices are cheaper than herbicide application. Most farmers rent spray machine toapply herbicide, and thus herbicide cost, sprayer rent, and labor charges are always expen-sive. In the long term, soil solarization is very economical and cost-effective. Currentfuel prices make things more difficult for farmers if power-driven machines are used forherbicide application. While polyethylene film is easily available and already in use for pro-tecting plants from chilling winter temperatures, solarization can be even more economicalwhen the available used polyethylene is reused. Keeping in view the long-term conse-quences of herbicide application and yield reduction, soil solarization is comparativelysafer and more economical in many areas with hot climate. Cost analysis indicated thatthe yield increases required to financially cover the expense of solarization in bare-groundand fall-mulch systems are generally less than the yield increases reported in previoussolarization research (Hasing, Motsenbocker, and Monlezun 2004).

Conclusions

Hand weeding or other methods are safe but not economical in many instances. Herbicidespose problems, such as herbicide resistance, weed shift, threat to biodiversity, carryovereffect, and superweeds (if herbicide-resistant varieties are grown). Thus, soil solarizationseems to be cost-effective, environmentally friendly, easy, and acceptable to the farming

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community, and no special precautionary procedures are needed. Vegetables are poor com-petitors because of their short stature and slow canopy closure; therefore, weeds severelyreduce their yield and quality. Keeping in view the importance of green organic vegeta-bles, solarization seems to be a promising means of weed control. As organic food garnershigher prices in the market, application of this method can be justified in many perspec-tives. Soil solarization is a simple method to practice after detailed scientific study for thefarming community.

Following are a few reasons why solarization should be considered for organic andweed-free nursery and vegetable production in Pakistan:

1. Weeds are one of the major concerns for nursery, vegetable, and other cash crop produc-tion in Pakistan. There is a scarcity of registered herbicides for use in nursery seedlingsor vegetable crops. The ones available are hazardous for vegetables and edible crops.Therefore, solarization can be successfully used for killing weed propagules.

2. Soil solarization can also be used for organic farming. However, organic farming is anew concept in Pakistan. Although there is a growing concern about overuse of pesti-cides, no practical direction has been given to organic farming enterprises. This methodprovides the best option and opportunity for those vegetable growers, nursery producers,home gardeners, and those who have concerns for the environment.

3. Most fields are left bare during the hot summer months, especially in areas having scarceirrigation water. This method can be successfully applied for weed control during thosemonths. In that case, farmers will not lose any crop as a result of their fields beingsolarized.

4. For nursery production, seeds are grown in nursery beds on a small scale. Thus, thismethod can be practiced without making drastic changes in the existing cropping systemor cropping pattern.

5. Methyl bromide is not common and easily available. Therefore, this process could bea successful alternative to control disease and kill vegetative propagules of differentweeds without any risk.

6. As solarization is a nonselective method of crop protection, it can be applied to controlsoil-borne pathogens, insect pests, and weeds simultaneously.

7. This method can be practiced in many parts of the country because a majority of themreceive plenty of intense sunshine for long periods.

8. Reduced plant growth in monoculture systems is attributed to accumulation in soil ofdetrimental biotic and abiotic agents, termed soil sickness. Solarization has the capabil-ity to solve this problem and improve plant growth (Gamliel, Hadar, and Katan 1989).Soil solarization also protects the environment from many threats, minimizes soil degra-dation and erosion, decreases pollution directly and indirectly, and optimizes biologicalproductivity.

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Soil Solarization: An Organic Weed-Management Approach in Cauliflower

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Transcript of Soil Solarization: An Organic Weed-Management Approach in Cauliflower