Weed control and yield response of soil solarization with different plastic films in lettuce

Phase out of most chemicals available for weed management renewed the interest in soil solarization as a technically effective and environmentally safe practice for lettuce weed control in hot summer areas. Properties of solarizing films and lettuce crop system may considerably affect weed control and yield response of soil solarization. Different solarizing films, including low-density polyethylene, ethylene-vinyl acetate copolymer, low-density polyethylene–ethylene-vinyl acetate coextruded and a biodegradable corn starch-based film, were evaluated in 2003 and 2004 for weed control and lettuce yield response under field and greenhouse conditions in Southern Italy. Soil solarization strongly reduced weed density and biomass in both greenhouse and in the field, with no significant differences among the tested plastic films. Most annual weeds were completely controlled by soil solarization, except amaranth, Amaranthus spp., in soil solarized with biodegradable film in the field. Emergence of mediterranean sweetclover, Melilotus sulcatus, was stimulated by soil solarization in greenhouse. In the field, Cyprus vetch, Lathyrus ochrus, was found in solarized plots though absent in untreated soil. Perennial weeds were not affected by soil solarization, except a strong control of canadian thistle, Cirsium arvense, in the field. Lettuce yield resulted significantly higher in solarized soil than in control plots, with no significant differences among the solarizing materials. All tested materials proved to be technically effective for soil solarization in lettuce, though low resistance and short durability of biodegradable film may suggest its application mainly to soil solarization in greenhouse or in organic systems.     

Effects of the radiometric properties of innovative biodegradable mulching materials on snapdragon cultivation

Research on the application of innovative biodegradable materials for substrate mulching in greenhouse floricultural cultivation was carried out in Southern Italy. A transparent biodegradable film and a transparent biodegradable spray coating were compared with a commercial transparent low density polyethylene film. The biodegradable film was a starch based extruded material, the sprayed coating was created from a polysaccharide solution. The materials were used to mulch the peat and perlite growing media contained in trays during snapdragon cultivation in order to increase the substrate temperature and hasten early growth. The climate variables inside and outside the greenhouse and the growing medium temperature under the mulching materials were recorded. Biometrical data, such as mean blooming time, plant height and spike length, were collected. The laboratory radiometric tests showed that the biodegradable mulching materials had a lower solar transmissivity in comparison to the low density polyethylene film. The capacity to reduce the long wave infrared thermal losses was higher for the biodegradable mulches: the long wave infrared transmissivity coefficient was 53.9% for the low density polyethylene film, 12.1% for the biodegradable film and 8.2% for the spray coating. The increase of the growing medium temperature allowed the harvest of the snapdragon grown in the mulched trays 7 days before that of the flowers grown in the un-mulched trays. At the end of the crop cycle the disposal of the biodegradable mulching materials was carried out fragmenting and mixing them with plant residue and the growing medium. The residue biodegraded in almost 1 month for the spray coating and in about 12 months for the biodegradable film.     

Effects of different mulches and irrigation methods on root growth,nutrient uptake,water-use efficiency and yield of strawberry

Field studies were conducted for two consecutive years under sub-temperate climatic conditions at Nauni in district Solan of Himachal Pradesh (30°52′N, 77°11′E 1175 asl) on loamy sand Inceptisols to investigate the effect of different mulches (hay: HM, black polyethylene: BP) on root growth, nutrient uptake, water-use efficiency (WUE) and yield of strawberry cv. Chandler under drip (DI) and surface irrigation (SI) systems. Unmulch (UM) and rainfed treatments were kept as control. Higher soil moisture content was registered under both the mulch materials during entire crop growth period. However, it was greater under BP mulch as compare to HM. The moisture conservation increased by 2.80–12.80% under BP mulch as compared to UM. HM treatment, irrespective of irrigation method increased the minimum soil temperature (2.8–5.2 °C) and reduced the maximum soil temperature (2.7–5.8 °C) as compared to UM. BP mulch increased the minimum soil temperature from 0.4 to 2.5 °C. Application of irrigation moderated the soil (minimum 2.6 and maximum 1.4 °C) temperature. Both the mulch materials were effective in enhancing root growth, nutrient uptake, WUE and yield. Application of mulch enhanced the root growth (63%), nutrient uptake (179.20%), WUE (84.40%) and yield (343%) under DI. However, respective increase under SI was 23.60, 83.80, 109.40 and 219.20%. Under DI, 51% of irrigation water was saved and about 19% higher fruit yield was obtained as compared with SI treatment. Linear regression model could significantly describe the variations in nutrient uptake (N, P and K) and WUE of strawberry under sub-temperate climatic conditions, root mass density was better indicator for estimating nutrient uptake of strawberry.     

Effects of plastic mulches on root zone temperature and on the manifestation of tomato spotted wilt symptoms and yield of tomato

Tomato spotted wilt (TSW) disease is a serious constraint to tomato production in various regions of the world. The effect of TSW on tomato yield is largely influenced by time of infection. Early infection usually results in severe stunting of the seedling and even death of the plant. Plastic film mulches affect both the incidence of TSW, and plant growth and yield of tomato. The objective of the present study was to determine the effect of root zone temperature (RZT) as affected by plastic film mulch on the manifestation of symptoms of TSW, and growth and yield of tomato plants either artificially inoculated with tomato spotted wilt virus (TSWV) or under natural TSW infection. In artificially inoculated plants as well as in plants under natural TSW infection, vegetative top fresh weight (FW) and fruit FW both increased with the length of time after transplanting that the plants remained free from TSW symptoms. The root zone temperature was highest under black mulch (seasonal mean = 27.5 °C), followed by gray (27.0 °C), silver (25.8 °C), and white (24.8 °C) mulches. The plants grown on black mulch showed the earliest appearance of TSW symptoms, and had significantly reduced vegetative growth and fruit yields compared to plants on the other mulches. In conclusion, utilization of plastic mulches that created conditions of high RZT stress resulted in reduced plant growth and yield and predisposed the plants to earlier expression of TSW symptoms compared to plants grown at RZTs more favorable to tomato plant growth (optimal RZT = 26.1 °C [Díaz-Pérez, J.C., Batal, K.D., Granberry, D., Bertrand, D., Giddings, D., Pappu, H., 2003. Vegetative top growth and yield of tomato grown on plastic film mulches as affected by the appearance of symptoms of Tomato spotted wilt virus. HortScience 38, 395–399]). Since these plant responses to TSW under heat stress occurred in artificially inoculated plants as well as in plants under natural TSW infection, high RZTs probably affected the plants directly, independently of any possible effects on the thrips vectors.     

Root aeration improves yield and water use efficiency of tomato in heavy clay and saline soils

Water logging and salinity of the soil alter both the physical and biological environment of plant roots. In two experiments, we investigated the effects of imposed aeration on yield and the physiological response of tomato (Lycopersicon esculentum L.) variety Improved Apollo growing under protected conditions over a range of salinities (the salinity experiment), and under constant field capacity (FC) or drier soil conditions (the moisture experiment). Subsurface irrigation with aerated water (12% air in water) stimulated above-ground growth, and enhanced the reproductive performance through earliness for flowering and fruiting compared with the control. Fruit yield of tomato with aeration in the moisture experiment was increased by 21% compared with the control (4.2 kg versus 3.7 kg per plant), and the effect of aeration on fruit yield was greater in FC than in the drier treatment. Fruit yield was increased by 38% in saline soil due to aeration compared with the non-aerated control. Increasing salinity from 2 to 8.8 dS m⁻¹, and 10 dS m⁻¹ reduced fruit yield by 18% and 62%, respectively, but 4 dS m⁻¹ did not suppress yield. Aeration in both the experiments increased plant water use and water use efficiency (WUE), expressed as weight per unit of applied water. Biomass WUE was greater by 16% and 32% in the moisture and salinity experiments, respectively. The increased yield with aeration was also accompanied by an increased harvest index (HI) defined as the proportion of dry fruit biomass to total dry biomass, greater mean fruit weight, high fruit DM, and increase in leaf chlorophyll content and shoot: root ratio, and a reduced water stress index (computed from the difference between air and leaf temperature). The benefit gained from aerating irrigation water was not only observed under conditions where air-filled porosity may be low (e.g., in poorly structure sodic soils, or at field capacity in clay soils), but also in drier soils.     

Root zone temperature,plant growth and yield of broccoli [Brassica oleracea (Plenck) var. italica] as affected by plastic film mulches

Plastic film mulches are often associated with increases in plant growth and yield of vegetable crops. Few studies, however, report on the effect of plastic film mulches on root zone temperature on broccoli. The objectives of this study were to determine the effects of colored plastic mulches on root zone temperature and broccoli plant growth and yield Broccoli (‘Packman’) plants were grown using plastic film mulch and drip irrigation. The treatments consisted of plastic film mulch (black, blue, gray on black, red, silver on black, and white on black mulches) and bare soil. Colored plastic film mulches affected root zone temperature and the accumulation of soil degree-days. Mean daily RZT, maximal daily RZT and degree day accumulation in the soil were highest in dark-colored mulches (blue, black, red, and gray) and lowest in light-colored mulches (silver and white), while minimal daily RZT was highest in silver mulch and lowest in white mulch. Silver mulch showed the smallest diurnal fluctuations in RZT among plastic mulches, with the highest RZT during the night and among the lowest in the afternoon. Colored plastic mulches also affected broccoli plant growth and yield, although the effect of mulches was more dramatic in the spring than in the fall seasons. Broccoli yield was linearly related to both the vegetative top dry weight and root dry weight of mature plants. Broccoli yield was little affected at mean RZT of <21 °C but increased with increasing mean RZTs above 21 °C up to 25 °C. Thus, broccoli plant growth and yield responded more favorably to dark-colored mulches than to light-colored mulches, suggesting that broccoli benefited from increased soil warming. No high RZT stress effects on broccoli plant growth or yield were observed in this study. Thus, this study suggests that plastic film mulches, particularly the dark-colored mulches, may be an option for spring broccoli production in areas with cool conditions early in the spring.     

Influence of soil hydrothermal environment,irrigation regime,and different mulches on the growth and fruit quality of strawberry (Fragaria × ananassa L.) plants in a sub-temperate climate

Summary

The present study was undertaken over two consecutive years under sub-temperate climatic conditions in the mid-hill region of Himachal Pradesh (30°52'N, 77°11'E; 1,175 m asl) on loamy sand Inceptisols. The aim was to investigate the effects of irrigation and mulch material on the growth, flowering, fruiting behaviour, relative leaf water content (RLWC), yield, and quality of strawberry (Fragaria × ananassa L. ‘Chandler’). The drip irrigation treatments included irrigation with 100, 80, or 60% (coded 1.0, 0.8, and 0.6 V) of the total water requirement. Both mulches increased the minimum soil temperature to a depth of 5 cm. The drip and surface irrigation treatments raised the minimum soil temperature by 3.0º – 5.4ºC, and lowered the maximum temperature by 2.2º – 5.8ºC compared to the rainfed control. Hay mulch was more effective in raising the minimum temperature and lowering the maximum soil temperature than black polyethylene mulch. Moisture conservation increased by 2.8 – 12.8% under the black polyethylene mulch compared to the no-mulch treatment. Drip and surface irrigation methods, as well as mulching, were found to be effective for enhancing the growth, irrigation water use efficiency (IWUE), fruit yield, and quality of strawberry plants. However, the number of crowns per plant, the percentage berry set, the RLWC, root length density (RLD), and fruit yield were highest under treatment M3I3 [i.e., black polyethylene mulch plus drip irrigation (1.0 V)] by 565.5%, 94.5%, 32.8%, 394.5%, and 549.6%,respectively, compared to the no mulch plus rainfed control. The maximum IWUE values for plant biomass [1.39 metric tonnes (MT) ha^–1 m^–1] and fruit yield (2.79 MT ha^–1 m^–1) were recorded under treatment M3I5 [i.e., black polyethylene mulch plus drip irrigation (0.6 V)]; whereas, the lowest values (0.39 and 0.68 MT ha^–1 m^–1, respectively) were observed using treatment M1I2 (i.e., without mulch, plus surface irrigation). Fruit size, weight, sugar content, and anthocyanin content increased significantly under treatment M2I3 [i.e., hay mulch, plus drip irrigation (1.0 V)] compared with all other treatments. Total soluble solids (TSS) contents and total acidity (TA) were highest under treatment M1I1 (i.e., no mulch, plus rainfed). A linear regression model could describe the variations in quality parameters of strawberry plants grown under sub-temperate climatic conditions. Root density was found to be the best indicator with which estimate fruit quality.     

可降解膜覆盖对小型西瓜产量和品质的影响

为了筛选适宜北京地区设施小型西瓜栽培使用的可降解覆盖材料,以黑色塑料地膜、黑色无纺布地膜(可降解)以及银色反光布地膜(可降解)为试验材料,研究了不同地膜覆盖对小型西瓜生育期、长势、根系活力、产量及品质的影响。结果表明:3种覆盖材料对西瓜产量的影响差异不显著,但黑色无纺布地膜覆盖处理下西瓜植株雌花开放较集中,根系活力、果实品质等指标优于其他处理,且可在6个月内降解。从效益、省工、环保等方面综合考虑,在北京地区早春大棚吊蔓栽培小型西瓜,建议选用黑色无纺布作为地膜覆盖材料。     

Greenhouse tomato limited cluster production systems: crop management practices affect yield

Limited-cluster production systems may be a useful strategy to increase crop production and profitability for the greenhouse tomato (Lycopersicon esculentum Mill). In this study, using an ebb-and-flood hydroponics system, we modified plant architecture and spacing and determined the effects on fruit yield and harvest index at two light levels. Single-cluster plants pruned to allow two leaves above the cluster had 25% higher fruit yields than did plants pruned directly above the cluster; this was due to an increase in fruit weight, not fruit number. Both fruit yield and harvest index were greater for all single-cluster plants at the higher light level because of increases in both fruit weight and fruit number. Fruit yield for two-cluster plants was 30% to 40% higher than for single-cluster plants, and there was little difference in the dates or length of the harvest period. Fruit yield for three-cluster plants was not significantly different from that of two-cluster plants; moreover, the harvest period was delayed by 5 days. Plant density (5.5, 7.4, 9.2 plants/m2) affected fruit yield/plant, but not fruit yield/unit area. Given the higher costs for materials and labor associated with higher plant densities, a two-cluster crop at 5.5 plants/m2 with two leaves above the cluster was the best of the production system strategies tested.     

不同覆盖方式对土壤肥力和马铃薯产量的影响

为了研究不同覆盖方式对土壤物理特性、有效养分以及马铃薯产量的影响,以早大白马铃薯为试验材料,设置常规露地（对照）和普通聚乙烯地膜、生物可降解膜、稻草3种覆盖方式,比较了不同时期土壤含水率、pH值、养分含量以及产量。结果表明：稻草覆盖保水效果最佳;生物可降解膜覆盖、稻草覆盖在马铃薯生长后期可提高土壤肥力,以生物可降解膜覆盖尤为明显,成熟期几乎所有速效养分指标均高于其他处理,与对照相比,土壤有机质、碱解氮、有效磷、速效钾含量分别高出7.49 g/kg、23.00 mg/kg、11.0 mg/kg、26.0 mg/kg。综合成本效益,除了稻草覆盖由于小薯多而效益比对照降低22.2%外,普通聚乙烯地膜覆盖和生物可降解膜覆盖比对照效益分别提高29.7%和24.2%。总之,普通聚乙烯地膜和生物可降解膜均可提高马铃薯产量和效益,但生物可降解地膜覆盖还可以改善土壤养分状况,减少环境污染,更具有推广价值。     

Influence of no-tillage and organic mulching on tomato (Solanum Lycopersicum L.) production and nitrogen use in the mediterranean environment of central Italy

In conservation tillage systems based on legume mulches it is important to optimize N management strategies. The present study evaluated the effect of some winter legume cover crops converted into mulches on the following no-tillage tomato (Solanum Lycopersicum L.) yield, tomato nitrogen uptake, tomato use efficiency (NUE), soil nitrate and the apparent N remaining in the soil (ARNS) in a Mediterranean environment. Field experiments were carried out from 2002 to 2004 in a tomato crop transplanted into: four different types of mulches coming from winter cover crops [hairy vetch (Vicia villosa Roth.), subclover (Trifolium subterranem L.), snail medic (Medicago scutellata L. Miller), and Italian ryegrass (Lolium multiflorum Lam.)]; a conventional tilled soil (CT); and a no-tilled bare soil (NT). All treatments were fertilized with three different levels of nitrogen (N) fertilizer (0, 75, and 150 kg N ha⁻¹). Cover crop above-ground biomass at cover crop suppression ranged from 4.0 to 6.7 t ha⁻¹ of DM and accumulated from 54 to 189 kg N ha⁻¹, hairy vetch showed the highest values followed by subclover, snail medic and ryegrass. The marketable tomato yield was higher in no-tilled legume mulched soil compared to no-tilled ryegrass mulched soil, CT, and NT (on average 84.8 vs 68.7 t ha⁻¹ of FM, respectively) and it tended to rise with the increase of the N fertilization level. A similar trend was observed on tomato N uptake. Hairy vetch mulch released the highest amount of N during tomato cultivation followed by subclover, snail medic, and ryegrass (on average 141, 96, 90 and 33 kg N ha⁻¹). The tomato NUE tended to decrease with the increase of the N fertilization rates, it ranged from 39 to 60% in no-tilled legume mulched soil and from −59 to 30% in no-tilled ryegrass mulched soil when compared to the CT. The soil NO₃-N content and the ARNS was always higher in the soil mulched with legumes compared to the soil mulched with ryegrass and in NT and CT. This study shows that direct transplanting into mulches coming from winter legume cover crops could be useful for improving the yield and the N-uptake in a no-tillage tomato crop. Furthermore, considering the high N content in the upper soil layer and the remaining N content in the organic mulch residues after tomato harvesting, there is a large amount of N potentially available which could be immediately used by an autumn–winter cash crop.     

鸡粪沼液复合微生物有机肥在温室樱桃番茄上的应用效果研究

为了探讨鸡粪沼液复合微生物有机肥在樱桃番茄上的田间应用效果,在滴灌施肥的条件下,设置化肥和液体复合微生物有机肥两个处理进行对比应用,结果表明施用液体复合微生物有机肥的处理其单果重可提高39.69％,含糖量可提高11.94％,茎粗可提高8.76％,Vc含量可提高5.72％,产量可提高30.95％,节约成本1.32％,可有...     

控水对日光温室樱桃番茄品质、产量和水分利用效率的影响

为了明确结果期水分调控对樱桃番茄产量和品质的影响，以千禧和红玉为试验材料，对不同土壤相对含水量（40%～50%、60%～70%、80%～90%）下日光温室冬春茬和秋冬茬樱桃番茄品质、产量和水分利用效率进行研究。结果表明，随着土壤相对含水量降低，樱桃番茄的果实可溶性固形物、可溶性糖、可滴定酸、VC 含量显著提高，水分利用效率也明显提高；但叶片净光合速率、气孔导度、叶绿素含量以及单果质量、产量随着土壤相对含水量降低呈现出先增加后降低的变化趋势。通过熵权法和TOPSIS 法相结合，综合分析樱桃番茄品质、产量和水分利用效率各项指标，得出樱桃番茄结果期最佳土壤相对含水量为40%～50%。     

Screening of AM fungi and Azotobacter chroococcum under natural,solarization, chemical sterilization and moisture conservation practices for commercial mango nursery production in north-west Himalayas

The present study investigates the performance of mango seedlings screened with indigenous arbuscular mycorrhizal (AM) fungi and Azotobacter chroococcum strains under solarized, chemical sterilized and natural soil conditions. Two isolates each of AM fungi namely, Glomus fasciculatum (Thaxter sensu Gerdemann) and Glomus mosseae (Nicol. & Gerd.), and two strains of A. chroococcum viz., A. chroococcum strain-I (AZ1) and A. chroococcum strain-II (AZ2) were inoculated at nursery stage under four different moisture conservation practices viz., black polyethylene mulch and organic mulches (grass mulch, cover crops, green manure) and clean cultivation. The observations on microbial population, root colonization, growth parameters and leaf nutrient content of the seedlings were recorded. Mango seedling's inoculated with G. fasciculatum and AZ1 had increased seedling's height, diameter, leaf area and total root length, microbial consortium of the rhizosphere soil and leaf N, P, K and Zn content in plots where solarization and black polyethylene mulching was used. The study revealed that the inoculation of mango stones and the saplings with G. fasciculatum and AZ1 under solarized black polyethylene mulched practice may be considered the best practice for raising mango nursery and maintaining soil health under rain-fed conditions of mid-hills of north-west Himalayas.     

水分胁迫对‘桂味’荔枝果实发育及糖代谢的影响

【目的】为研究水分胁迫对荔枝果实的生长发育、糖代谢及产量的影响,【方法】以15 a生‘桂味’荔枝(Litchichinensis Sonn‘Guiwei’)为试材,设以灌溉和水分胁迫2个不同的土壤水分处理。【结果】结果表明,水分胁迫下荔枝果实的大小、单果质量降低,果实发育受到抑制。水分胁迫的荔枝坐果率显著降低,同时导致最终产量的下降。对水分胁迫条件下糖积累的研究发现,‘桂味’荔枝前期以积累还原糖为主,果实发育后期主要积累蔗糖;胁迫处理的荔枝果实糖含量前期低于灌溉的,后期总糖、蔗糖及还原糖含量都高于灌溉处理的。在荔枝果实发育后期,分解蔗糖的酸性转化酶(AI)、蔗糖合成酶(SS)及合成蔗糖的蔗糖磷酸合成酶(SPS)的活性都为水分胁迫的高于灌溉处理的,这将有助于增加胁迫的果实库强及糖的积累。【结论】因此为使果实正常生长及提高产量和品质,生产上果实发育前中期应保持足量均衡的水分供应,后期不需要过多水分。     

Water requirement,crop coefficient and water-use efficiency of ‘Robusta’ banana under different soil covers and soil moisture regimes

Provision and soil covers in a ‘Robusta’ banana plantation considerably reduced consumptive use of water and number of irrigations needed throughout the period of crop growth. Consumptive use ranged from 1024 mm under 800-gauge thick black polyethylene cover at 60% depletion of available soil moisture to 1560 mm under no cover treatment at 20% depletion. There was a perceptible increase in water-use efficiency under soil covers at low available soil moisture depletion levels. Soil covers reduced the periodic crop coefficient values compared with bare soil, indicating the reduced (23–33%) water requirement of banana plants under soil covers. High crop coefficient values recorded up to 5 months after planting indicated high consumptive use of water during that period. Using the crop coefficient values and corresponding period reference crop evapotranspiration, periodic water requirement of ‘Robusta’ banana for profitable production could be estimated.     

Fruit thinning in ‘Conference’ pear grown under deficit irrigation: Implications for fruit quality at harvest and after cold storage

Fruit thinning in pear is feasible for mitigation of water stress effects. However, it is not well known how fruit quality at harvest and after cold storage is affected by pre-harvest water stress. Even less is known about the effects of fruit thinning on quality under these circumstances. To elucidate these, we applied deficit irrigation (DI) and fruit thinning treatments to ‘Conference’ pear over the growing seasons of 2008 and 2009. At the onset of Stage II (80 and 67 days before harvest in 2008 and 2009, respectively), two irrigation treatments were applied: full irrigation (FI) and DI. FI trees received 100% of crop evapotranspiration (ETc). DI trees received no irrigation during the first three weeks of Stage II to induce water stress, but then received 20% of ETc to ensure tree survival. From bud-break until the onset of Stage II and during post-harvest, FI and DI trees received 100% of ETc. Each irrigation treatment received two thinning levels: no thinning leaving commercial crop load (∼180 fruits tree⁻¹), and hand-thinning at the onset of Stage II leaving a light crop load (∼85 fruits tree⁻¹). Under commercial crop loads, DI trees were moderately water-stressed and this had some positive effects on fruit quality. DI increased fruit firmness (FF), soluble solids concentrations (SSC) and acidity at harvest while no changes were observed in fruit maturity (based on ethylene production). Differences in FF and acidity at harvest between FI and DI fruit were maintained during cold storage. DI also reduced fruit weight loss during storage. But fruit size was reduced under DI. Fruit thinning under DI resulted in better fruit composition with no detrimental effect on fresh-market yield compared to un-thinned fruit. Fruit size at harvest and SSC values after five months of cold storage were higher in fruit from thinned trees than fruit from un-thinned trees. Fruit thinning increased fruit ethylene production, indicating advanced maturity. This may lead to earlier harvest which is desirable in years with impending drought. Fruit thinning is therefore a useful technique to enhance pear marketability under water shortage.     

Response of hybrid muskmelons to polyethylene row covers and black polyethylene mulch

Four commercial and two experimental muskmelon hybrids were grown with four different treatments: (1) bare soil, (2) black polyethylene mulch, (3) clear polyethylene row cover, and (4) a combination of row cover and mulch. The row cover alone afforded slightly better frost protection than the row cover—polyethylene mulch treatment. Daytime temperatures under the row covers averaged 4–5° C above outside air temperatures. Soil temperatures were considerably higher under the row cover—polyethylene mulch treatment than the other treatments.All hybrids commenced pistillate flowering earlier with the row cover treatments than with bare soil or black polyethylene mulch, and the experimental hybrids flowered comparatively much earlier than the commercial hybrids with the row cover—polyethylene mulch treatment. Fruit maturity was 3–9 days earlier for the commercial hybrids and 12–13 days earlier for the experimental hybrids with the row cover—polyethylene mulch treatment than with black polyethylene mulch.The results suggest considerable potential for increasing earliness in muskmelons in northern regions through the use of polyethylene mulches in combination with row covers, and by breeding cultivars more adapted to these cultural methods.     

The effects of alternatives to soil residual herbicides on weed control,yield and quality of hops

Summary

Several non-chemical methods of weed control in hops (Humulus lupulus) were evaluated in a three-year study. The results show that the use of cultivation, grass and winter rye cover crops, straw and plastic mulches all gave satisfactory weed control in both alleyways and hop rows. Data are presented on the effects of the main treatment groups, on the yield, alpha-acid content and alpha yield of hops. The effects on other hop cone quality criteria are also reported. Cultivation to control weeds had to be timely, and by the end of the study, numbers of weeds germinating in the spring were increasing. The use of a winter rye cover crop was successful in reducing over-wintering weed populations in cultivated plots. Grass reduced yield but raised the alpha-acid content of the cones, resulting in no overall loss in yield of alpha-acid. Yield reductions were overcome by adding extra nitrogen as an early spring top dressing, but this tended to reduce alpha-acid content to give similar alpha yields. Analysis of soil mineral nitrogen contents of soils to 90 cm depth in spring and autumn indicated that extra spring nitrogen was readily taken up by grass swards, helping to overcome its competitive effect on the hop plants. Winter rye reduced soil mineral nitrogen levels although this failed to reach statistical significance (P>0.05) but this nitrogen was returned to the soil when the cover was cultivated out in spring. Straw mulches tended to raise alpha-acid levels enough to raise alpha yield one year by 5% compared with conventional residual herbicide, although this failed to reach statistical significance (P>0.05). The implications of the results to growers of hops are discussed.     

Effects of deficit irrigation on biomass,yield, water productivity and fruit quality of processing tomato under semi-arid Mediterranean climate conditions

Processing tomato is a high water demanding crop, thus requiring irrigation throughout growing season in arid and semiarid areas. The application of deficit irrigation (DI) strategies to this crop may greatly contribute to save irrigation water. A two-year study was carried out in order to assess the effects of DI upon water productivity, final biomass, fruit yield and some quality traits of open-field processing tomato cv. Brigade in a typical semi-arid Mediterranean environment of South Italy. Four irrigation treatments were studied: no irrigation following plant establishment (V0); 100% (V100) or 50% (V50) evapotranspiration (ETc) restoration up to fruit maturity, 100% ETc restoration up to flowering, then 50% ETc restoration (V100-50). Total dry biomass accumulation was significantly depressed by early soil water deficit in V0; irrigation at a reduced rate (50% ETc) from initial stages (V50) or from flowering onwards (V100-50) did not induce any losses in final dry biomass. The marketable yield did not significantly differ among plots irrigated, but an averaged irrigation water saving of 30.4% in V100-50 and 46.2% in V50 was allowed as compared to V100. Marketable yield was negatively affected by the early water shortage in V0, due to the high fruit losses (>44%). The effects of DI on fruit quality were generally the converse of those on fruit yield. DI improved total soluble solids content, titratable acidity and vitamin C content. Water use efficiency was positively affected by DI, suggesting that the crop does not benefits from the water when this last is supplied to fulfil total crop requirements for the whole season. Yield response factor, which indicates the level of tolerance of a crop to water stress, was 0.49 for total dry biomass (Kss) and 0.76 for marketable yield (Ky), indicating that in both cases the reduction in crop productivity is proportionally less than the relative ET deficit. In conclusion, the adoption of DI strategies where a 50% reduction of ETc restored is applied for the whole growing season or part of it could be suggested in processing tomato, to save water improving its use efficiency, minimizing fruit losses and maintaining high fruit quality levels. This aspect is quite important in semi-arid environments, where water scarcity is an increasing concern and water costs are continuously rising.