effect of soil solarization on corn stalk rot

Plant and Soil 179: 17-24, 1996. 17 (~) 1996 Kluwer Academic Publishers. Printed in the Netherlands.

Effect of soil solarization on corn stalk rot

Yasmin A h m a d 1, A. H a m e e d 2 and M. A s l a m 1 l Crop Diseases Research Institute, National Agricultural Research Centre, Park Road, P.O. NIH, lslamabad, Pakistan and 2Department of Biological Sciences, Quaid-i-Azam University, Islamabad, Pakistan *

Received 3 January 1995. Accepted in revised form 4 October 1995

Key words: Chilo partellus, corn (Zea mays L.), Fusarium graminearum, Fusarium moniliforme, Macrophomina phaseolina, stalk rot

Abstract

Seven weeks solarization of irrigated soil raised its temperature by 11.5 °C over non-solarized soil at 10 cm depth and effectively controlled weeds (98.5%), stalk borer (8.9%) and stalk rot disease (69.1%) in corn. Solarization also reduced symptoms of Fusarium moniliforme and Macrophomina phaseolina significantly by 64.2% and 78.4%, respectively, and completely controlled M. phaseolina in corn cultivars, viz. Pool- 10, Shaheen and Gauher. Whereas symptoms of F. moniliforme were observed in these cultivars, Fusarium graminearum was not observed except in two cultivars, Shaheen and Akbar. Growth of crop planted in solarized plots was better and it yielded almost one to three times more grains in cultivars under test. Soil analysis immediately following solarization revealed that essential elements were readily available in simpler forms, which may have increased pest resistance and reduced stalk breakage.

Introduction

Soil solarization is a relatively new mulching tech- nique for hydrothermal disinfestation (Katan et al., 1976). Moist soil is covered with transparent polyethylene film during the summer (Stapleton et al., 1985) and heated by solar radiation for several weeks (Sta- pleton and Garza-Lopez, 1988). It is used to control soil-borne pests in regions with high temperature and intense solar radiation (Mahrer et al., 1987; Naot et al., 1987). Solarized soils frequently suppress certain soil- borne pathogens and weeds (Greenberger et al., 1987; Powles et al., 1988; Rubin and Benjamin, 1984; Sta- pleton and Garza-Lopez, 1988), especially in the top 10 cm soil (Ben-Yephet, 1988; Lazarovits et al., 1991).

Since soil solarization reduces the number of fun- gi, bacteria, nematodes, insects and weeds, it often results in increased plant growth response, yield and fruit quality (Buercky, 1988; Kaewruang et al., 1989; Kim and Han, 1988; Lazarovits et al., 1991; Sivakumar and Marimuthu, 1987) even in the absence of known pathogens (Chen and Katan, 1980; Katan, 1981; Sta-

* FAX no: + 9251811381

pleton and DeVay, 1984). Solarization may affect the chemistry of the soil, increasing quantities of mineral nutrients in solution (Chen and Katan,1980; Daele- mans, 1989; Kaewruang et al., 1989; Stapleton et al., 1985) and decreasing soil salinity (Abdel-Rahim et al., 1988). Moreover solarization is cheaper than fumigation and other pesticide use. Thus, soil mulching is economical, simple, safe, involves no phytotoxicity or pesticide residues (Bandara, 1987) and does not require sophisticated machines (Jacobsohn et al., 1980).

The purpose of this study was to investigate the effects of soil solarization on stalk rot, stalk borer and grain yield in different corn cultivars having different maturity groups. Changes in soil nutrients (both macro- and micro-nutrients) and other soil character- istics (temperature, pH, EC and OM) were also evaluated.

Materials and methods

A field experiment was conducted during summer 1990 in soils naturally infested with stalk borer (C. partellus)

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and common pathogens (E moniliforme, E graminearum, M. phaseolina) at the National Agricultural Research Centre (NARC), Islamabad, Pakistan. Six corn cultivars with three different maturity groups, early (E) (Pool-10 and Shaheen), medium (M) (Gauher and Faisal) and late (L) (Sarhad white and Akbar) were hill-planted in either solarized or non-solarized plots measuring 7.5 m 2. Hills were spaced 0.25 m apart within 0.75 m spaced rows. The trial was a split plot arrangement in randomized complete block design with four replications. Solarization, maturity group and cultivars were main plots, sub-plots and sub-sub-plots, respectively.

All plots were pre-irrigated, and then mulched treatments were covered with transparent polyethylene film (0.04 mm thick). No pesticide was applied. Before mulching, temperature probes were inserted into the soil of all treatments at depths of 10, 20 and 30 cm. Temperature was measured daily during the soil solarization period by using a temperature recorder every day at 1400 hr. Soil was kept moist during treatment to increase thermal sensitivity of any resting forms of pathogens and improve heat conductivity (Katan et al., 1976). Solarization started on June 6, 1990 and lasted 53 days. Polyethylene sheets were removed on July 29, 1990, one day before sowing.

After the polyethylene film was removed, soil samples were immediately collected with a standard 4 cm (inside diameter) core auger. Four cores were collected per replication and bulked by three depth ranges (0- 10, 10-20, and 20-30 cm). Soil samples were air dried, crushed in mortar pestle and sieved through 150 #m pores before chemical analysis. Bulked soil samples for each treatment, depth and replication were analysed for macro- and micro-nutrients using an ammo- nium bicarbonate - diethylene triamine pentaacetic acid (ABDT-PA) extraction (Soltanpour and Workman, 1979). Ten g of soil was extracted with 20 mL ABDT- PA solution in 250 mL conical flask and shaken for 15 min before filtration. Undiluted extract was used to analyse the macro-elements (NO3 -N, P, K) and (1:10) dilutions were used for micro-nutrients (Zn, Cu, Mn and Fe). The pH of the soil was determined potentio- metrically in a mixture of soil and distilled water (1 part soil : 1 part water, w/v). The same paste (1:1) was used for electrical conductivity (EC).

Control of weeds was evaluated by counting number of weeds m -2 in both solarized and non-solarized plots. Disease severity (%) was assessed in each treatment at harvest (16 wk after planting). Stalks were split lengthwise and the degree of rot spread rated on

a 0-to-5 scale (Hooker, 1957), where 0 indicated no rot, 1 = 1-25% of internode damage, 2 = 26-50%, 3 = 51-75%, 4 = 76-100% and 5 = 100% with symptoms extending into an adjacent internode.

Stalk rot values were scored separately for each pathogen on the basis of discolouration and symptoms produced. M. phaseolina produced black sclerotia on the vascular bundles, E graminearum produced an internal pink to reddish discolouration of the dis- eased tissue along with shredding of the pith, and E moniliforme produced light pink discolouration of the pith. The stalk borer C. partellus produced tunnels and excretions and was scored based on the length of the tunnels.

Grain yield was also recorded 16 wk after planting in November 1990. Yield was based on weight of shelled grains at 15% moisture.

Disease data on the 0-to-5 scale were transformed to percentages for statistical analysis. Data were analysed by analysis of variance (ANOVA) and Duncan's multiple range test (DMRT) for both disease severity and grain yield (kg ha- l) in different treatments.

Soil temperature, pH, EC, OM and mineral nutrients (macro- and micro-nutrients) at three different soil depths (0-10, 10-20 and 20-30 cm) were also analysed statistically in both solarized and non-solarized plots.

Results

Weed population including Setaria sp. foxtail, Sorghum halepense, Echinochloa colona and Cype- rus rotundus was controlled (98.5%) in solarized plots throughout the summer growing season (Table 1). By contrast, the non-solarized plots had to be hand- weeded several times during the experiment.

The most important physical effect of soil mulching with transparent polyethylene film (0.04 mm thick) was increase in soil temperature, especially in the upper lay- ers of the soil. With increasing soil depth soil temperature decreased (p = 0.05). Average soil temperatures in the top layer of solarized plots reached 39.2 °C at 10 cm soil depth, about 11.5 °C higher than non-solarized plots (27.7 °C) (Table 2). Soil analysed immediately after removal of the polyethylene film was higher (p = 0.05) in soil K and Mn (22.4 mg kg -1 and 0.5 mg kg -1, respectively) at the 10 cm depth (Table 3). This increase in K and Mn in solarized plots was due to high moisture contents in the soil, which increased solubility of these nutrients.

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Table 1. Effect of soil solarization on weed population at 60 days after planting

Weeds Weed counts

Solarized Non-solarized % decrease

plots plots over control

(no. m -2) (no. m -2)

Setaria sp. 0.0 21.0 100

Sorghum halepense 0.0 35.0 100

Cyperus rotundus 3.0 50.0 94

Echinochloa colona 0.0 18.0 100

Mean 0.75 31.0 98.5

Table 2. Effects of soil solarization on soil temperature, pH, and electrical conductivity at three vertical strata of soil during summer 1990

Soil depth Temperature (°C) pH (1 : 1)

(cm) S x NS y S NS

EC z (mmhos c m - I )

S NS

0-10 39.2a 27.7d 7.2a 7.2a 1.8a 1.8a

10-20 34.3b 26.3e 7.2a 7.3a 1.8a 2.0a

20-30 30.6c 25.2f 7.2a 7.3a 2.1a 1.9a

Means of a parameter with the same letter are not significantly different (p = 0.05) according to Duncan's multiple range test. xS = Solarized plot. YNS = Non-solarized plot. zEC = Electrical conductivity

Plants were only slightly affected by E graminearum in solarized plots, whereas in non-solarized plots symptoms were comparatively severe in cv. Akbar. Symptoms of other pathogens F. moniliforme and M. phaseolina as well as stalk borer (C. partellus) were all decreased by solarization (Table 4).

E moniliforme was the most damaging with an average disease severity of 14.4% and 13% in E cultivars Pool-10 and Shaheen, 8.5% and 7.2% in M cultivars Gauher and Faisal and 14.3% and 2.7% in L cultivars Sarhad White and Akbar planted in the non- solarized plots (Table 4). The pathogen was significantly (p = 0.05) reduced by solarization, especially in E cultivars (Table 5). M. phaseolina was also reduced significantly in solarized plots. Severity scores of this pathogen were reduced by up to 100% in cultivars, viz., Pool-10, Shaheen and Gauher (Table 5).

Grain yield in the experimental plots was significantly lower in non-solarized plots. Of all the cultivars

tested Pool- 10 (E) and Gauher (M) had the highest rel- ative grain yield production with 271% and 263%, respectively. Other cultivars showed almost double grain yield over non-solarized plots (Table 6).

Discussion

A pronounced reduction in weed population was observed soon after removal of the polyethylene sheets and was still significant for 4 months after planting during the summer growing period (Table 1). These results are in agreement with other findings (Rubin and Ben- jamin, 1983; Stapleton, 1991). Solarization controls weeds and reduces soil-borne pests, conserves moisture and improves other soil physico-chemical charac- teristics. In our studies it also increased the availability of essential nutrients in the soil and hence enhanced the growth of corn plants. This is in agreement with

20

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other studies regarding increased soil nutrients following soil solarization (Chen and Katan, 1980; Rovira, 1976).

In solarized plots mean temperature at 10 cm soil depth was observed to be 11.5 °C higher than in non- solarized plots. This increase in soil temperature in solarized plots was normal, as has also been reported by other workers from Israel (Horowitz et al., 1983; Jacobsohn et al., 1980; Katan, 1981), Califor- nia (Pullman et a1.,1981), Canada (Lazarovits et al., 1991), Mexico (Stapleton et al., 1985; Stapleton, 1991) and Pakistan (Zaki and Ghaffar, 1989). We observed that variation in temperature at different soil depths was greatly influenced by weather conditions (cloudy, sunny, rainy days with different air temperature and humidity). These observations agree with the findings of Katan (1981) and Mahrer (1979), who stated that temperatures in mulched soil vary with air temperature, humidity, radiation, wind velocity and soil char- acteristics.

Our studies revealed that EC and pH were least affected by solarization (Table 2), whereas differences were observed in soil nutrients OM, NO3-N, NH4-N, K and Mn between solarized and non-solarized plots. According to these observations, OM content of the solarized plots appeared to be less than that of non- solarized plots at all soil depths (Table 3). Total N contents were consistently the same in both solarized and non-solarized plots, whereas NO3-N levels were higher in the solarized-plots in comparison with those in non-solarized plots at all soil depths. On the other hand, NI-In-N levels in the solarized plots were greatly reduced as compared to those in non-solarized plots (Table 3). Moreover, K and Mn levels were higher in solarized plots, especially in the top 10 cm soil depth, whereas other nutrients such as P, Zn, Cu and Fe were least affected (Table 3).

The NO3-N and EC differences we observed agree with the findings of Kumar and Yaduraju (1992), who reported that solarization resulted in increased concentration of nitrogen compounds and reduced EC of the soil. However, concentrations of NO3-N and NH4-N were not increased up to 6 times in solarized plots, as discussed earlier by Stapleton et al. (1985).

Stapleton et al. (1985) reported that solarization did not consistently affect available K +, Fe 3+, Mn 2+, Zn 2+, Cu 2+ or C1- concentrations, soil pH or total organic matter. Kaewruang et al. (1989) reported that solarization increased the levels of NO3-N and NH4-N in soil, but did not affect the concentration of PO~3-, K +, Fe ++, organic C and pH.

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Table 5. Effect of soil solarization on symptoms typical of given corn pathogens

Treatment Disease reduction (%) Maturity Cultivar Fusarium moniliforme Fusarium graminearum Macrophomina phaseolina stalk rot Chilo partellus group (fungal pathogen) (fungal pathogen) (fungal pathogen) (total disease) (stalk borer)

Early Pool- 10 (cv I ) 13.0 0.0 0.6 13.7 2.8 (-90.3) (0.0) (- 100) (-91.3) (- 100)

Shaheen (cv2) 9.5 1.4 9.3 20.1 +4.2 (-73.1) (-53.8) (- 100) (-81.0) (+200)

Medium

Late

Gauher (cvl) 8.0 0.0 1.8 9.8 +1.0 (-94.1) (0.0) (- 100) (-95.1) (+500)

Faisal (cv2) 3.8 0.0 6.6 10.5 0.0 (-52.8) (0.0) (-78.6) (-66,9) (0.0)

Sarhad white (CV 1) 6.0 0.0 2.0 7.9 3.0 (-42.0) (0.0) (-50.0) (-43.2) (-60.0)

Akbar (cv2) +1.8 3.6 5.0 6.8 0.8 (+66.7) (-75.0) (-62.5) (-43.9) (-57,1 )

(-) = % decrease over control. (+) = % increase over control.

Table 6. Effect of soil solarization on grain yield in corn cultivars having different maturity groups

Treatments Grain yield (kg ha- 1 ) Maturity Cultivar Solarized Non-solarized % increase

plots plots over control

Early Pool-10 (CVl) 2577.6cdef 694.9f 271.0 Shaheen (cv2) 3265.5bcde 1830.3def 78.4

Medium Gauher (CVl) 4460~5abc 1227.7ef 263.3 Faisal (cv2) 5530.2a 2654.1cdef 108.4

Late Sarhad white ( c v 2 ) 3766.5abcd 1555.1ef 142.2 Akbar (cv2) 4877.8ab 2427.5cdef 100.9

Means of a parameter with the same letter are not significantly different (p = 0.05) according to Duncan's multiple range test. Statistics of individual values conducted separately

Soil solarizat ion was an effective method in con- t rol l ing stalk rot. Disease caused by M. phaseolina was a lmost 100% control led in three cultivars, viz. pool-10 (E), Shaheen (E) and Gauher (M) planted in solarized plots. Field observat ions revealed stronger

stalks in a lmost all cul t ivars planted in treated plots. Soil analysis showed that more potash (k) in treated plots, especial ly in the upper soil levels, may make stalks stiffer and stronger. As solarization provided

high moisture contents in the solarized plots, solubil i- ty of K was increased, which may have increased pest resistance and reduced stalk breakage.

Shaheen and Gauher cult ivars p lanted in solarized plots were more sensit ive to stalk borer (C. partellus.). Susceptibil i ty to E moniliforme was also related to this insect which damaged the plants, perhaps enhanc ing penetrat ion of pathogen in L cv. Akbar.

No herbicide was used immediately after planting; thus, plant performance was very poor in non-solarized plots. In treated plots, grain yield was more than double due to pathogen control, enhanced available nutrients in the soil as well as no competetion with weeds. Thus, solarization could be beneficial for integrated disease management systems in future.

Acknowledgement

The authors are grateful to Dr T L Righetti, Oregon State University, USA for his guidance and valuable suggestions.

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Section ediwr: R Rodriguez Kabana

effect of soil solarization on corn stalk rot

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