The effects of a non-woven cover in combination with different soil mulches in strawberry cultivation Abbas Aflatuni Agricultural Research Centre ofFinland, North Finland Research Unit, North Ostrobolhnia Research Station, FIN-92400 Ruukki, Finland, e-mail: abbas.aflatuni@mtt.fi Riitta Kemppainen Agricultural Research Centre of Finland. North Finland Research Unit, Kainuu Research Station, FIN-88600 Sotkamo, Finland Alpo Heinonen Agricultural Research Centre ofFinland, North Finland Research Unit, Lapland Research Station, FIN-96900 Saarenkylä, Finland Tiina Hakonen Agricultural Research Centre ofFinland, Data and Information Services, FIN-31600 Jokioinen, Finland The effects of a non-woven cover and three different soil mulches on the timing of harvest and on the yield of strawberry were examined in two field experiments in northern Finland during 1989-1993. The non-woven cover was used either in spring or in both autumn and in spring. Non-covered plants served as controls. Depending on the year, plants covered in spring alone gave a significantly earlier (4 to 9 days) marketable yield than did uncovered plants. The non-woven cover had no effect on marketable yield at Sotkamo but at Rovaniemi it increased the yield, especially in cold years. The use of cover decreased the amount of mouldy berries. At both experimental sites, a significantly higher yield was obtained from beds covered with soil mulches than from uncovered beds. White-on-black film delayed the yield by 2 to 4 days in comparison with black or Mypex film. Key words: black film, early harvest, Mypex film, quality, timing, white-on-black film ntroduction Non-woven covers are mostly used under cool conditions to advance strawberry crop growth early in the season (Laurinen and Säkö 1987, Davies 1992). A non-woven type of cover, such as Agryl or Lutrasil, provides a barrier against pest attack (Davies 1992). Begin (1988) found that plants ripened more quickly on plots cov- ered with polypropylene-polyamide net (Agronet) in spring than on uncovered plots. According to Polling et al.( 1991), overwinter covers improved early yields, but not the total © Agricultural and Food Science in Finland Manuscript received May 1997 371 Vol. 6 (1997): 371-380. AGRICULTURAL AND FOOD SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=_dWOSVtKI2mwlBnG.sJCa8mz6SffBk-X9DPvBpQ.BIF53pmpW27InFiAiYK8SZ-sFQkEbewHozvl6pRcAnYSTbL2Y1PdYZ-jxUxoY01-Du931_NSWZl7SgCXcOk6cY9IzOqU3CxEeeanHlRNVJ9W5CBEDzOJZP4z9wgnQl9N460gn4jJZXAQUt0sEzK5P667naLPFarSyw_JBVsWGMDyUaw81GjIxPF9fO40RDoAror6cttoIcfOEdKwQiI0qUDJP8z3wwDAlZ7kinx3YhQj8P5eRydFPEvBfMPEdHdw91dRhks1qMniiahwWFHQnywHktGGRSESIAhqcaEFCKrVcP2hu5O7s67d6tUKEf6MUjWrJNN8 Aflatuni, A. et al. A non-woven cover and soil mulches in strawberry cultivation marketable yield. Laurinen and Säkö (1987) re- ported that non-woven covers have, however, certain disadvantages, e.g. a slightly poorer crop quality and a large percentage of small berries (less than 1.5 cm in diameter), both of which reduce the quantity of the marketableyield. Pol- lard (1990) noted that Agronet row covers (ex- truded polypropylene-polyamide mesh) en- hanced conditions in autumn and spring, thus possibly contributing to greater flower initiation and berry development. Clear polyethylene plas- tic over plants in spring creates a greenhouse effect, which advances the start ofgrowth in ear- ly spring. This early growth results in earlierbud development and, subsequently, an earlier har- vest, which, as shown by experience, is approx- imately 7 to 10 days earlier than that for organ- ically mulched plants (Scheel 1982). The most widely used soil mulch is black PE film. One disadvantage of black film is that it warms up the soil surface. The strawberry roots are then drawn closer to the soil surface than in uncovered soil, making the plants more suscep- tible to freeze injury (Leskinen 1977). The sur- face temperatures of clear, black and white plas- tic mulches were 17, 19 and 15°C higher, respec- tively, than the surface temperature of bare soil. Both clear and black mulches advanced the ear- liness of the crop, increasing the potential dan- ger from late spring frosts (Himelrick 1982). The temperature under mulch alone was highest for clear polyethylene and lowest for aluminium- coated paper, with black polyethylene being intermediate between the two. Row covers over black polyethylene gave a higher soil tempera- ture than did black polyethylene alone (Voth 1968). Generally, the superiority of plants on black polyethylene mulch was well sustained in the second year, the average yield being almost 90% higher than that from plants grown on bare soil (Laughlin 1968). Clear mulch increased fruit maturity by about 1 week, and black mulch by about 3 days, whereas white mulch had no ef- fect on the time of maturity (Hopen and Oebker 1976). Pollard et al.(1987), Pollard and Cundari (1987), Pritts et al.(1989), Lieten (1991) and Himelrick et a1.(1993) reported that in northern areas with short growing seasons and/or low- temperature stress during winter or spring, spun- bonded row covers of clear or black polyethyl- ene advanced the strawberry harvest and im- proved strawberry yields in matted rows by in- creasing the growing degree units and by reduc- ing heat loss from beneath the covers. The main aim of this study was to answer the following questions: 1) Does the use of a non-woven cover or soil mulches or their combination advance harvest? 2) Is the yieldof a crop protected by a non-woven cover in spring or in both autumn and spring greater than that of an uncovered crop? 3) Does the use of soil mulches increase the mar- ketable yield? 4) Does black polyethylene mulch cause strawber- ry roots to grow nearer the soil surface than in bare soil? Material and methods Field studies were conducted in 1989-1993 at two stations in northern Finland, Sotkamo (64°06’N, 28°20’E) and Rovaniemi (66°35’N, 26°01’E). The characteristics of the experimen- tal soils are presented in Table 1. At Sotkamo fertilizer was applied to the rows before bed shaping at rates of N 0, P 0, K 206 kg/ha, and at Rovaniemi at N 112, P 168 and K 184 kg/ha in accordance with the general recommendations of the Soil Analysis Service of Finland. The most commonly cultivated early straw- berry in northern Finland is ‘Zefyr’, a variety of Danish origin. Plants of this variety were plant- ed in June 1989 in rows of about 15 cm high and 5 m long. The rows were spaced 130 cm on cen- Table 1. Characteristics of experimental soils. Sotkamo Rovaniemi pH 6.76.8 P, mg/1 soil 35.039.7 K, mg/1 soil 214.0225.0 Ca, mg/1 soil 2025.02027.0 Mg, mg/1 soil 231.0438.0 372 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Table 2. The periods that strawberry plants were protected with a non-woven cover in spring and autumn. Station 1991 1992 1993 Sotkamo 5 May -17 June 13May- 11 June 7 May -31 May 12Aug-16Sept HAug-23Sept 30Aug-lOct Rovaniemi 14 May- 24 June 18May- 9 June 15 May -9 June 5 Sept - 5 Nov 1 Sept - 1 Nov 31 Aug -23 Sept tre, and were covered with three different soil mulches: woven cloth (Mypex film), black plas- tic film and white-on-black plastic film. The Mypex film is woven from polypropylene plas- tic strips and provide effective protection against UV-radiation. Water penetrates the film, which is 200 p thick, weighs 95 g/m2 and is 100 cm wide. The black film, which is of UV-protected polyethylene is 60 p thick. The white-on-black film is coextruded polyethylene, 100 p thick. Non- covered plants served as controls. In combination with mulches, a non-woven cover (Lutrasil 17 g/m2 , white in colour with 92% light infiltra- tion) was applied at two different times.The first application was in spring after the snow had melted and immediately after spring cleaning; this cover was left in place until flowering be- gan. The second application was in autumn, and was used to extend the autumn season and pro- tect the plant from early frosts. This cover was applied in August, after the harvest, and left in place until October; it was put back on again in spring. Table 2 shows the periods that the straw- berry plants were covered with the non-woven cover in spring. Calculation and observation methods An early harvest was established by calculating how many days had elapsed from the first har- vest day until the day when at least half of the marketable yield had been harvested. The total yield was classified into marketable yield, small berries, mouldy berries and others. Berries less than 1.8 cm in diameter were considered small. The quantity of small berries in the early har- vest and the total yield were calculated. At the end of the experiment, the plants were removed carefully with their roots intact to find out wheth- er roots under mulches grow at the soil surface or deeper down. The roots were washed and their length was measured. The region ofroot branch- es was examined and each root was assessed on a scale from 1 to 5. If the roots were mostly branching on the upper side, they were rated I and if they were mostly branching on the down- side, they were rated 5. Weather conditions The plants received sufficient moisture from rainfall, and irrigation was therefore unneces- sary. During the growing season, temperature and precipitation were monitored. Table 3 lists the monthly mean precipitation during growing sea- sons, Figure 1 shows the average temperatures from May to October in 1991-1993, and Figure 2 the sum of effective temperature (base °C) at Sotkamo and Rovaniemi. Soil temperature measurement At Rovaniemi, the temperature of the soil was measured under cover and under mulches. The measurements were made at 7.00 am, at a depth of about 15 cm. The differences in temperature be- tween soils under cover and uncovered soils dur- 373 Vol. 6 (1997): 371-380. AGRICULTURAL AND FOOD SCIENCE IN FINLAND Aflatuni, A. et al. A non-woven cover and soil mulches in strawberry cultivation Table 3. Monthly mean precipitation during growing seasons in 1991-1993 and long-term averages. Precipitation, mm Station Month 1991 1992 1993 1961-1990 Sotkamo May 50.7 19.5 20.8 38.4 June 149.0 26.9 56.7 55.5 July 45.5 71.2 112.3 67.8 August 60.7 139.5 77.0 88.5 September 85.4 84.0 62.4 63.5 Sum May-September 391.3 341.1 329.2 313.7 Rovaniemi May 72.3 34.9 41.6 34.4 June 94.0 109.6 59.5 54.4 July 22.1 117.5 53.1 63.4 August 60.3 147.4 31.5 68.6 September 68.3 96.1 23.4 61.0 Sum May-September 317.0 505.5 209.1 218.8 Fig. 1.Average of monthly temperature a) at Sotkamo and b) at Rovaniemi. Fig. 2. Sum of effective temperature a) at Sotkamo and b) at Rovaniemi (base°C). 374 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Table 4. The 5-day average temperature (OC) under different soil mulches and crop covers at 7.00 am at Rovaniemi in 1991 and 1992. Treatment 16-20 May 21-25 May 26-30 May 31 May -4 June 5-9 June Mypex & Lutrasil 6.508.95 9.5111.88 11.61 Black & Lutrasil 6.769.28 9.9312.10 12.10 White on black & Lutrsil 5.908.16 8.8711.12 11.18 Lutrasil 6.588.50 9.3411.40 11.30 Mypex 5.307.39 7.8010.25 10.36 Black 5.677.82 8.0910.42 10.60 White on black 4.456.73 6.729.21 9.41 No mulch or cover 4.776.80 6.829.32 9.51 ing May and June were similar. The highest tem- peratures were recorded with Mypex film and the non-woven cover or with black film and the non-woven cover (Table 4). Pesticide use At Sotkamo and Rovaniemi, supermetrin (Ripcord 0.05%) was used against leaf beetle (Galerucella sagittariea) in 1991, 1992 and 1993. At Sotkamo tridimefon (Bayleton 0.03%) was used against powdery mildew (Sphaewtheca alchemillae) in 1992 and 1993. At Rovaniemi there was no need to spray the plants against the above mentioned fungi and insects. Statistics The day at which 50% of the marketable yield was achieved, was assessed with 2 subsequen- tial harvest days. The first day was when 50% of the marketable yield had not yet been achieved and the second day was when it had just been achieved. The days were usually 2 to 5 days apart. A linear estimation was used to establish the time that had passed before 50% of the mar- ketable yield was achieved. The statistical analysis was performed using analysis of variance (ANOVA) for a split plot design. The non-woven cover was the mainplot, and the soil mulch was the subplot. The model included a time factor, the year of harvest, which was considered as a sub-subplot. The covariance structure for repeated measures was selected from unstructured, autoregressive and compound symmetry using the Akaike Information criteri- on (SAS 1992).The analysis was performed with theMIXED procedure of the SAS® software. The response variable was log-transformed, when necessary, to satisfy the statistical assumptions of the ANOVA. A P-value of less than 0.05 was considered statistically significant. Results Timing of the harvest Effects ofnon-woven cover The effect of the non-woven cover on the timing of harvest was significant at both experimental sites (Table 5). Effects ofmulches The use of mulches had a significant effect on the timing of harvest at both experimental sites. At Sotkamo, in all 3 years, the effect of black film was statistically significant (P