Weight Of Lettuce Research Articles

The effect of light quality on growth of lettuce

Plant factory is a plant production system with controlled temperature, carbon dioxide concentration and light environment to enhance plant growth efficiently. Fluorescent lamp is popularly used in a plant factory, however, the spectrum of fluorescent light is broad and some portion of them is not necessary for photosynthesis. On the other hand, LED (light emitting diode) has narrow band width and is getting easy to use these days. The final goal of this project is to develop a new light apparatus with LEDs for plant factory. The specific objective is to investigate the effective light quality for growing plant more rapidly. The effect of light generated by monochromic and mixed radiation from LEDs (blue, green, red) on the response of lettuce (Lactuca sativa L.) were evaluated and compared with the effect of lettuce irradiated by fluorescent lamps. Photosynthesis rate of lettuce increased in monochromic red light and the light mixed with red and blue light. Number of leaves decreased in monochromic blue light. Fresh weight of lettuce was increased in monochromic red and fluorescent light, but monochromic red light significantly decreased dry weight rate. In the view of energy saving, LED is much better than fluorescent lamp. Especially, red LED is good.

Effect of Inorganic and Organic Germanium Treatments on the Growth of Lettuce (Lactuca sativa)

Germanium (Ge) is a rare heavy metal and is known to toxic to plants at high level. However, there is little evidence about the Ge effect on plant growth. Here, we investigated the effect of inorganic (GeO2) and organic (Ge-132) germanium on lettuce growth by treatment with various concentrations of GeO2 and Ge-132. Under GeO2 treatment, lettuce growth was not much inhibited at 2.5 mg/L concentration and then significantly inhibited at 5 mg/L concentration. However, under Ge-132 treatment, lettuce growth was not much inhibited by concentrations up to 10 mg/L. Relative fresh weight of lettuce at 2.5, 5, 10 and 25 mg/L concentrations was 99, 76, 65 and 35% in GeO2 treatments and was 105, 99, 97 and 75% in Ge-132 treatments, respectively. In GeO2 treatments, Ge was highly accumulated in the roots at concentration below 10 mg/L and in the shoots at concentration above 25 mg/L. However, Ge was primarily accumulated in the roots at all Ge-132 concentrations. Accumulated Ge amounts of plants under GeO2 treatment were 0.72 mg/ g DW in roots and 0.27 mg/ g DW in shoots at a 10 mg/L concentration. At a 50 mg/L concentration of GeO2, the Ge content was 0.77 mg/g DW in roots and 1.58 mg/g DW in shoots, respectively. Based on our results, inorganic germanium is more toxic for lettuce growth than organic germanium. Upper critical toxic levels for lettuce growth were 2.5 to 5 mg/L concentrations in GeO2 treatments and 10 to 25 mg/L concentration in Ge-132 treatments, respectively.

Effect of Maturation of Grease Trap Compost On Plant Growth

Although it is known that immature composts can depress plant growth, few studies have quantified this effect in real-world scenarios with field-grown crops. Glasshouse and field trials were used to investigate the effect of maturation of grease trap compost (GTC) on plant growth. Grease trap waste was composted for 7-14 d in an in-vessel reactor with shredded green waste, sawdust and chicken manure and matured in windrows for up to 6 weeks. In the glasshouse trial, compost samples were mixed with an equal volume of coarse sand and were compared with a standard mix of 3 parts composted pine bark to 1 part coarse sand (v/v). In these trials, fresh GTC suppressed germination and growth of both radish and alyssum compared to the standard mix. Two weeks maturation reduced phytotoxicity of GTC but it was still phytotoxic relative to the standard mix. After 6 weeks maturation, GTC performed as well as the standard mix in all measures of plant growth and germination except for plant height of alyssum. Fresh and mature GTC were also used as soil conditioners in field trials on a commercial vegetable farm in the Werribee irrigation district, Victoria, Australia. Treatments consisted of GTC at 5 or 10 t ha−1, nil compost or a pelletised poultry manure product (Zest®) at 618 kg ha−1 arranged in a factorial design with 100% and 75% of the grower's standard fertilizer rate (741 kg ha−1 Rustica-Plus®). Head weight of lettuce was significantly reduced (by up to 18%) by the application of 10 t ha−1 of fresh GTC at the grower's standard fertiliser rate. When the fertiliser rate was reduced to 75%, the negative impact of fresh GTC was less apparent. In contrast to the first crop, the performance of mature GTC compared to the controls was independent of fertilizer rate (soil amendment x fertilizer interaction not significant at p<0.05). Application of 5 and 10 t ha−1 of mature GTC increased head weight of lettuce by 11% and 12% respectively compared to the control plus Zest® treatment. This research highlights the need of a better understanding of the maturity requirements of composts for use as soil amendments and growing media in horticultural production.

Row Covers Reduce Insect Populations and Damage and Improve Early Season Crisphead Lettuce Production

Insect damage on cripshead lettuce (Lactuca sativa L.) can reduce its marketability and cause significant crop losses. There is increasing interest in using alternative control strategies to replace or reduce pesticide use for this purpose. Crisphead lettuce cv. Ithaca grown under two densities 10 (ARC10) and 17 (ARC17) g/m2 of polypropylene applied as floating covers or low tunnels were compared with an uncovered control. Effects on tarnished plant bugs and aphids, air and soil temperature, and lettuce growth and development were recorded. Aphids and tarnished plant bug were almost completely excluded by covers. Once removed, insect population in the covered treatments increased but was 5.5 times less than in uncovered control. Covered plots had higher air and soil temperatures than uncovered plots. Air temperatures were higher under the floating covers than tunnels. ARC17 had higher soil temperatures than ARC10. Row covers promoted earlier growth and maturity. Head weights of lettuce covered with ARC17 were 1.4 times heavier than those of ARC10, which in turn were heavier than the control. Head weights were similar for floating covers and low tunnel treatments.

Integrated Agro-Economic Approach to Deficit Irrigation on Lettuce Crops in Sicily (Italy)

The effect of four different irrigation levels on the marketable yield and economic return of summer-growth lettuce was evaluated during 2005 and 2006 in Eastern Sicily, Italy. The viability of deficit irrigation was evaluated by estimating optimum applied water levels. Actual evapotranspiration ( ETa ) was estimated by combining pan evaporation measures and the Penman–Monteith approach ( ET0-PM ) . The highest marketable yield of lettuce was recorded for plots receiving 100% ET0-PM . For deficit irrigated plots, reductions in crop production were ascribed to a decrease in lettuce weight. Crop coefficients equal to 1 determined maximum crop production values. Crop water use efficiency was maximum at a 100% ET0-PM level of water applied, corresponding to yield of 0.3 t ha−1 mm−1 . Irrigation water use efficiency reached its maximum at a 40% ET0-PM level, with values of 0.54 and 0.44 t ha−1 mm−1 during 2005 and 2006, respectively. Water applied and marketable yield of lettuce showed a significant quadratic ...

Bioconversion of squid pen by Lactobacillus paracasei subsp paracasei TKU010 for the production of proteases and lettuce growth enhancing biofertilizers

A protease-producing bacterium, strain TKU010, was isolated from infant vomited milk and identified as Lactobacillus paracasei subsp. paracasei. A surfactant-stable protease, purified 64-fold from the third day culture supernatant to homogeneity in an overall yield of 11%, has a molecular weight of about 49,000. The enzyme degraded casein and gelatin, but did not degrade albumin, fibrin, and elastin. The enzyme activity was increased about 1.5-fold by the addition of 5 mM Ba 2+. However, Fe 2+ and Cu 2+ ions strongly inhibited the enzyme. The enzyme was maximally active at pH 10 and 60 °C and retained 94% and 71% activity in the presence of Tween 20 (2% w/v) and SDS (2 mM), respectively. The result of identification of TKU010 protease showed that nine tryptic peptides were identical to Serratia protease (serralysin) (GenBank accession number gi999638) with 35% sequence coverage. In comparison with the tryptic peptides of L. paracasei subsp. paracasei TKU012 protease, TKU010 protease possessed two additional peptides with sequences of AATTGYDAVDDLLHYHER and QTFTHEIGHALGLSHPGDYNAGEGNPTYR. The fourth day culture supernatant of TKU010 showed maximal activity of about 5-fold growth enhancing effect on lettuce weight, which was not shown with L. paracasei subsp paracasei TKU012.

A Growth Model for Leaf Lettuce under Greenhouse Environments

A growth model for leaf lettuce grown in a greenhouse environment was developed. The experiments were conducted in a plant production facility located at Ibaraki University, Japan from January to November 2003. Each experiment took 37 days, namely 7 days for germination and 30 days after transplanting to a hydroponic system. The combinations of photosynthetic photon flux density of 140 to 200 μmol m−2 s−1 and CO2 concentration of 400 and 1200 μmol mol−1 were varied as the experimental treatments. Lettuce weights were measured 2 to 3 times a week, and the weight and number of leaves at harvest, 30 days after transplanting, were measured. A model was developed to fit the growth data using the Gompertz function, which has three coefficients. We found two of the three coefficients can be fixed at certain values within the range of our experimental conditions, and the last coefficient is closely related to fresh weight at harvest. An accurate prediction of lettuce weight at any number of days after transplanting can be achieved. The developed growth model shows a typical growth curve to thirty days as transplants respond to the input environmental conditions. Using this model, growers can identify when their plants will attain the desired target weight based on their greenhouses' environmental settings. This model may be applicable as a tool for planning production schedules and to help management strategy.

주류생산 부산물인 주박의 특성 규명 및 주박이 작물생육에 미치는 영향

본인들은 주류생산 부산물인 주박을 이용한 친환경적인 비료를 개발하고자 한다. 본 시험에 사용된 주박에는 잔존 알코올함량이 평균 5-8%이며, 주요성분으로 6.04% 총질소량, 42.59% 총탄수화물량, 1.01% 유용 인산량, 73.42% 유기물량, 7.72% <TEX>$K_2O$</TEX>, 1.35% CaO와 0.53% MgO을 함유하고 있었다. 주박은 980 units/g의 <TEX>${\alpha}-amylase$</TEX>, 300 units/g의 glucoamylase와 1,800 units/g의 산성 protease활성을 나타내어 비교적 높은 수준의 효소 활성을 나타내었다. 토양으로부터 분리한 미생물 중 항 진균활성이 우수한 근권세균인 Bacillus subtilis KMU-13을 분리, 생화학적 특성과 16s rDNA 분석에 의하여 Bacillus subtilis KMU-13으로 동정했다. 식물병원성 진균인 Botrytis cinerea KACC 40573, Sclerotinia sclerotiorum KACC 41065, Fusairum of oxysporum KACC 40052, Pythium aphanidermatum KACC 40156, Phytophthora capsici KACC 40476와 Glomerella cingulata KACC 40299에 대하여 높은 항 진균활성을 나타내었다. 시제품은 동결건조 주박을 직접 시제품으로 사용하는 시제품 1과 동결건조 주박 20%, 담체 70%, B. subtilis KMU-13의 배양액 9.7%, 미량원소 0.3%를 혼합하여 시제품 2를 제작했다. 시제품 1과 시제품 2의 상추를 이용한 포장 재배시험에 대한 비료효과 및 토양이화학성 변화를 조사한 결과, 3요소비료, 퇴비 및 석회를 시용한 관행구에 비해 수확기의 엽장, 엽폭, 엽수 및 생체중량 등이 증가하였으며, 토양 이화학성의 변화는 거의 없었다. This experiment was conducted to develop fertilizer which promotes plant growth as well as suppressing pathogenic fungi. The fertilizer was made from the mixture of Ju-Back (Korean rice wine cake) and indigenous rhizosphere-bacterium. The main ingredients of Ju-Back were investigated as 6.04% total nitrogen, 42.59% total carbohydrate, 1.01% available phosphate, 73.42% organic matter, 7.72% potassium oxide, 1.35% calcium oxide, 0.53% magnesium oxide. The enzyme activities of Ju-Back were estimated to be 980 units/g for <TEX>${\alpha}-amylase$</TEX>, 300 units/g for glucoamylase, and 1800 units/g for acid pretense. Indigenous rhizosphere bacteria which produced antifungal agent were isolated from soil, and was selected KMU-13 strain which can antagonize against various plant pathogenic fungi (Botrytis cinerea KACC 40573, Sclerotinia sclerotiorum KACC 41065, Fusairum oxysporum KACC 40052, Pythium aphanidermatum KACC 40156, Phytophthora capsici KACC 40476 and Glomerella cingulata KACC 40299). KMU-13 strain was identified as Bacillus subtilis KMU-13 by biochemical and 16s rDNA analysis. The organic fertilizer was made as prototype which was composed 20% Ju-Back, 70% carrier, 9.7% microorganism cultivated solution, 0.3% trace-element. We also investigated an application of fertilizer using Ju-Back for cultivating lettuce (Lactuca sativar) which were grown in three soil conditions that had chemical fertilizer, barnyard manure, lime power, urea, potassium chloride and superphosphate as a control, the whole quantity (80 kg/10a) of posted fertilizer with the control and the half quantity (40 kg/10a) with the control. The growth characteristics were examined and analysed with several weeks interval from 3 weeks to 8 weeks on head length (cm), head width (cm/head), number of leaf and fresh weight (g/plant). The results are summarized as follows. The head width and fresh weight of lettuce were the highest at posted fertilizer 1 (whole quantity) was applied chemical, organic matter (Ju-Back) and carrier. The head length was the highest at posted fertilizer 2 (whole quantity) was applied Ju-Back only.

Reducing microbial contamination on wastewater-irrigated lettuce by cessation of irrigation before harvesting.

To assess the effectiveness of cessation of irrigation before harvesting in reducing microbial contamination of lettuce irrigated with wastewater in urban vegetable farming in Ghana. Assessment was done under actual field conditions with urban vegetable farmers in Ghana. Trials were arranged in completely randomized block design and done both in the dry and wet seasons. Seven hundred and twenty-six lettuce samples and 36 water samples were analysed for thermotolerant coliforms and helminth eggs. On average, 0.65 log units for indicator thermotolerant coliforms and 0.4 helminth eggs per 100 g of lettuce were removed on each non-irrigated day from lettuce in the dry season. This corresponded to a daily loss of 1.4 tonnes/ha of fresh weight of lettuce. As an input for exposure analysis to make risk estimates, the decay coefficient, k, for thermotolerant coliforms was 0.66/day for the wet season and 1.49/day for the dry season. In combination with other measures for improving water quality, the measure can significantly reduce faecal contamination of lettuce during the dry season. However, it is not suitable for the wet season due to unfavourable conditions for pathogen die-off and re-contamination by splashes from contaminated soils. The results provide a good basis for risk assessments and for devising more appropriate measures for risk reduction, especially in sub-Saharan Africa.

OPTIMIZATION OF LIGHTING SPECTRUM FOR PHOTOSYNTHETIC SYSTEM AND PRODUCTIVITY OF LETTUCE BY USING LIGHT-EMITTING DIODES

OPTIMIZATION OF LIGHTING SPECTRUM FOR PHOTOSYNTHETIC SYSTEM AND PRODUCTIVITY OF LETTUCE BY USING LIGHT-EMITTING DIODES

Humic acid applications to lettuce do not improve yield but do improve phosphorus availability

The effects of humic acid (HA) and phosphorus (P) applications on plant growth and nutrient content of lettuce, together with available soil phosphorus remaining after harvest were examined. The amounts of phosphorus used were 0, 120, and 240 kg ha−1 and those of humic acid were 0, 100, 200, and 300 kg ha−1. Phosphorus increased the nitrogen content of lettuce significantly (P<0.01) while the application of humic acid did not have significant effect. Humic acid, phosphorus, and HA×P interaction increased the nitrogen content of lettuce significantly (P<0.05). All effects were not significant for plant K, Ca, Mg, Fe, Cu, and Mn contents. Application of phosphorus decreased Zn content significantly (P<0.05). Increased amount of phosphorus caused significant increases in residual soil phosphorus (P<0.01). It was concluded that the application of 120 kg ha−1 of phosphorus together with 300 kg ha−1 of humic acid was convenient for the head weight of lettuce.

Effects of Phosphorus Fertilization on the Area of Influence of Common Lambsquarters (Chenopodium album) in Lettuce

Area-of-influence experiments were conducted on high–organic matter soils to assess the effect of common lambsquarters distances from ‘South Bay’ lettuce on yield and quality under two phosphorus (P) regimens. P was applied either banded (125 kg P/ha) or broadcast (250 kg P/ha) before lettuce planting. Lettuce plants were harvested at 0, 25, 50, 75, 100, and 125 cm from each side of the common lambsquarters plant after season-long interference. The regression equations were y = 0.40 + 0.36/(1 + e−0.09(x−52.5)),r2= 0.92, for banded P; and y = 0.40 + 0.29/(1 + e−0.07(x−69.3)),r2= 0.94 for broadcast P. Banded P produced 9% more fresh weight per head than the broadcast P treatment under weed-free conditions. Within the broadcast P treatments, common lambsquarters growing at 125 and 100 cm did not affect fresh weight of harvested lettuce. Values for fresh weight per head declined 18, 34, 38, and 38% when lettuce grew at 75, 50, 25, and 0 cm distance from common lambsquarters, respectively. Fresh weight of lettuce in banded P treatments was reduced only at 50, 25, and 0 cm distance from common lambsquarters plants, representing 31, 44, and 44% less than its weed-free control, respectively. Banding P at 50% (125 kg/ha) of the recommended broadcast rate reduced the area of influence of common lambsquarters with lettuce.

Effect of food waste compost on microbial population, soil enzyme activity and lettuce growth

The effect of food waste (FW) composted with MS ® (Miraculous Soil Microorganisms) was compared with commercial compost (CC) and mineral fertilizer (MF) on bacterial and fungal populations, soil enzyme activities and growth of lettuce in a greenhouse. Populations of fungi and bacteria, soil biomass, and soil enzyme activities in the rhizosphere of FW treatments significantly increased compared to control (CON), CC and MF treatments at 2, 4, and 6 weeks. The fresh weight of lettuce in FW treatments was about 2–3 times higher than that in CC at 4 and 6 week. The pH, EC, total nitrogen content, organic matter and sodium concentration in FW treatments were generally higher than those in CON, CC and MF treatments.

Plastic mulches and row covers for early and midseason crisphead lettuce produced on organic soils

Plastic mulches and row covers for early and midseason crisphead lettuce (Lactuca sativa L. ‘Ithaca’) grown on organic soils were investigated over 2 yr. For early production, four mulch treatments (infrared transmitting, silver-on-black co-extruded polyethylene, white-on-black co-extruded polyethylene and a bare soil control) with and without an agrotextile low tunnel were tested. For midseason production, the same mulch treatments were evaluated in combination with normal and high planting densities (54 400 plants ha-1 and 65 200 plants ha-1). Low tunnels combined with mulches accelerated early growth and maturity by 10 d for infrared-transmitting mulch, 7–8 d for silver mulch and 3–5 d for white mulch, relative to production on bare soil control without a low tunnel. Infrared-transmitting mulch alone increased plant biomass early in the season and produced a lettuce head of heavier or similar weight relative to that from bare soil, even if harvested 3–4 d earlier. Lettuce heads grown on silver and white mulches were harvested 1–3 d earlier, and were 22% heavier in the first year and 29% heavier in the second year than when grown on bare soil. Head weights of lettuce under the low tunnels were higher than those from control plots in the first year only, and head size was similar in both years. For midseason production, infrared-transmitting and silver mulches accelerated the early growth of lettuce, but resulted in heads with long cores at maturity, particularly with infrared-transmitting mulch. Silver mulch increased the percentage of marketable heads in the first year and head weight and size at maturity in the second year, and reduced the incidence of aphids in both years, relative to plots without mulch. White mulch resulted in larger and heavier heads than those produced without mulch in the second year, and produced heads with shorter cores than those produced with other mulches in both years, even during particularly hot growing conditions. The percentage of marketable heads was similar for both the high- and low-density plantings and, as a result, the former produced more marketable heads per hectare. However, lettuce plants grown at the higher density were smaller in the second year. During conditions conducive to disease development in the first year, higher density plantings were more susceptible to downy mildew. Key words: Lactuca sativa, iceberg lettuce, muck soils, plasticulture, mini-tunnel, physiological disorder, planting densities

Greenhouse Broccoli and Lettuce Growth Using Cocomposted Biosolids

The benefits of compost applications on various soil types were demonstrated in greenhouse studies. A compost prepared from yard waste feedstock cocomposted with biosolids at a 1:1 ratio was used to grow broccoli (Brassica oleracea botrytis, var. ‘Brigadeer’) and leaf lettuce (Lactuca sativa, var. ‘Lallorosa’) at 0, 15, 30, and 60 dry tons per acre (t/a). Surface soil from three dominant regional soil types (Arnold loamy sand, Goleta loam and Todos-Lodos clay loam) was used in plastic pots in the greenhouse studies.All rates of compost applications increased the height and dry weight of broccoli shoots and dry weight of lettuce shoots in the various soil textures tested. In loam and clay loam soil, optimal rates of compost applications were 30 to 60 t/a for broccoli and 15 to 30 t/a for lettuce. In loamy sand soil, optimal rates for broccoli and lettuce were 30 and 15 t/a, respectively. Broccoli showed less phytotoxicity symptoms to higher compost loads than did lettuce, probably because of more tolerance...

Influence of Phosphorus Fertility on Intra- and Interspecific Interference between Lettuce (Lactuca sativa) and Spiny Amaranth (Amaranthus spinosus)

Greenhouse studies were conducted to determine the effect of phosphorus (P) fertility on intra- and interspecific competition between lettuce and spiny amaranth for 4 wk after emergence. Total lettuce shoot biomass per pot and weight per plant increased 39 and 44% in response to increased P fertility, respectively. P fertility had no impact on growth of spiny amaranth. Total shoot biomass of spiny amaranth increased with increasing density from four to eight plants, however, lettuce did not. Total shoot biomass of both species increased as density increased from 4 to 16 plants. Spiny amaranth, but not lettuce, weight per plant decreased in response to intraspecific competition. Reciprocal yield analysis showed that spiny amaranth produced 2.4 times more biomass than lettuce when competing intraspecifically and four times more biomass under interspecific competition. Lettuce weight per plant was not affected. Relative yield analysis indicated that spiny amaranth was more competitive than lettuce regardless of P fertility. However, increased P fertility increased competitiveness of lettuce. Relative crowding coefficients indicated that spiny amaranth at the low density with low P fertility was 33 times more competitive than lettuce. Addition of P caused lettuce and spiny amaranth to be equally competitive at the lowest density; however, at the highest density, spiny amaranth was 4 tunes more competitive than lettuce regardless of additional P.

Effects of temperature on the growth of lettuce (Lactuca sativa L.) and the implications for assessing the impacts of potential climate change

Stands of lettuce were grown from a single transplanting in the field within two double-walled polyethylene tunnels along which temperature gradients were imposed. Plant dry weight was initially higher in the warmer plots, but maximum dry weight of lettuces grown under cooler condi tions was ultimately higher. Plant relative growth rate declined during ontogeny. This decline increased with increasing temperature. A simple growth model of this response is described in which the optimum incident radiation and optimum temperature for instantaneous relative growth rate are constant. but the maximum potential relative growth rate declines with developmental thermal time. This model was optimized using data from two plots, and predicted accurately the observed increase in the dry weight of lettuce grown in 14 independent plots. The potential effects of six scenarios of climate change on the yield of lettuce grown from this transplanting date was assessed using this model. Calculated maximum yields, averaged over 15 years, ranged only between a 6 per cent reduction and a 5 per cent increase compared to the present baseline climate depending on which climate change scenario was used. The time from transplanting to a lettuce of marketable fresh weight was reduced (by up to 9 days) under all six scenarios.

Relationship between Corky Root Disease and Yield of Crisphead Lettuce

The effects of corky root (CR) disease, caused by Rhizomonas suberifaciens(van Bruggen, Jochimsen, and Brown) on fresh and marketable weights of lettuce (Lactuca sativa L.) were assessed during the 1988 and 1989 cropping seasons in several commercial lettuce fields. The resistant crisphead cultivars Raleigh and South Bay and the susceptible cultivars Ithaca and Shawnee produced similar yields in fields either planted in lettuce for the first time or in continuous lettuce production for three cropping cycles. Average yields of the resistant cultivars, from two fields cropped for six cycles naturally infested with CR, ranged from 875 to 1062 g/head fresh weight and 674 to 907 g/head marketable weight. The average yields of the susceptible cultivars in these infested fields ranged from 419.8 to 668.7 g/head fresh weight (37% to 52% yield loss) and 317.5 to 488.2 g/head marketable weight (46% to 53% yield loss). CR severity ratings were highly negatively correlated with root dry matter accumulation and whole and marketable head weights of-lettuce.

Influence of block and cell size, growing medium and insecticide dose on the behaviour and uptake of phorate by lettuce and uptake of carbofuran and chlorfenvinphos by calabrese

AbstractPhorate residues in peat blocks and lettuce were determined following incorporation of the insecticide into different block and ‘Speedling’ cell sizes. Between‐block variability was influenced little by block size. Phorate oxidation was most extensive in the largest blocks containing the smallest dose. Total residue concentrations in the lettuce declined from the time of planting to harvest, although accumulation of insecticide continued and was related more to dose than to block or cell size. Residues in the lettuce at harvest exceeded the proposed maximum limit of 0.2 mg kg−1 in some treatments. Residues at planting comprised mainly the parent sulphoxide and sulphone, but by harvest, the oxygen analogue sulphoxide and sulphone predominated. Lettuce weight was not influenced by dose but was related directly to block size.Carbofuran and chlorfenvinphos residues were determined in calabrese sown into two sizes of blocks. At planting time, carbofuran residue concentrations were 100 times greater than those of chlorfenvinphos but residues of both insecticides in the mature heads were &lt; 0.01 mg kg−1. Seedling weights in both sowings declined with increasing concentrations of the insecticides.It was concluded that manipulations of block size and the dose of insecticide need to be evaluated for individual insecticide/crop combinations to exploit the technique fully.

Lettuce tipburn as related to the cation contents of different plant parts

The effects of various cations on the incidence of tipburn in lettuce were studied. For that purpose lettuce was grown in soil in an experiment in which two concentrations of various salts were added to the irrigation water. The quantities of the salts were selected in such a way that the total ion concentrations were the same for all the salts,i.e. 25 and 50 mmol.l−1. The tipburn levels were assessed visually and at harvest, crop samples were collected from various parts of the plants and analysed for sodium, potassium, calcium and magnesium. The application of sodium bicarbonate in the irrigation water had a significantly greater effect on the fresh weight of lettuce than the other salts. There were no significant differences between the effects of the other salts. The greater effect of sodium bicarbonate may be attributed to sodicity. The relationship between the results of the tipburn assessments and the cation contents of the various plant parts were examined in different ways. The highest correlation coefficients were obtained with multiple linear regression equations in which calcium, magnesium and sodium were included as independent variables. The correlation coefficients for the analytical results of the various plant parts ranged between 0.88 and 0.91. The correlation coefficients for the analytical results of the various potassium was used instead of sodium as the third independent variable. This is probably the result of the fact that sodium and potassium were highly correlated in the crop analyses.