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Iron is dissolved in water in the form of ferrous oxide and is transformed into ferric oxide during pumping, an oxide that is suspended in the water in particles of 0.5 microns and more, the build-up of which will clog drippers.

When ferrous oxide levels get too high

Iron bacteria grow in an anaerobic environment. In contact with oxygen, the oxidation of iron and the death of bacteria cause the appearance of an orange gelatinous mass that may clog drippers. This contamination of iron-rich groundwater is difficult to precisely predict. However, above an iron (ferrous oxide) level of more than 1.5 ppm (1.5 g/l), an iron removal plant should be installed.

Sand filters

Various sand filter methods can be used. The most effective is the injection of air into an oxidation tower and then filtration of the ferric oxide particles either via a sieve or disc filters or, better still, sand filters with automatic backwash. Sand filters are preferable for long-term drip installations. It should be noted that their use significantly raises the pH of the water, something that needs to be taken into account for ferti-irrigation. Successive waterfalls and settling in a basin before pumping and filtration are also a possible solution. Injection of caustic soda (aqueous solution of sodium hydroxide) is also possible. In short, In the presence of iron, the operation of drip irrigation requires increased vigilance and high-performance equipment to ensure the efficiency and sustainability of the installation.

Michigan is the largest producer of asparagus in the United States, providing spears both for processing and the fresh market. In spring, asparagus is direct seeded into a nursery and grown for one year. The resulting crowns are then transplanted into production fields and a limited number of harvests take place until the third year of growth. Michigan’s asparagus is harvested from May through June after which the fern develops. Fusarium crown and root rot (FCRR) disease of asparagus causes wilt, fern chlorosis, vascular discoloration, root rot, and crown death significantly reducing yields. Unfortunately, fusarium is a persistent and pervasive soil plant pathogen in Michigan’s asparagus growing region, making management difficult. Cultural and chemical control options are limited.

Michigan’s growers have been treating crowns

Fusarium spp. prefer poorly drained soils and humid climates. The pathogen may be disseminated by wind, rain splash, and soil movement and is resistant to harsh conditions, surviving on plant residues and in the soil for 20 years or more. Limiting disease caused by Fusarium spp. includes removing asparagus crop residues from fields and cleaning machinery between fields, managing weed hosts, minimising plant stress, and practising crop rotation. Treating crowns with fungicides before planting and fumigating crown nurseries and production fields are methods that have been used by Michigan growers in recent years.

New active ingredients to better manage purple spot

Purple spot on asparagus spears and ferns is also a significant problem for asparagus producers in Michigan. Purplish lesions may affect 60-90 % of the spears, rendering them unmarketable. The emergence of this disease occurred with the adoption of a no-till cultural system. Due to the sporadic nature of disease occurrence, fungicide cost, and lack of control with some fungicide spray programs, it was desirable to apply fungicides according to a disease forecaster. TOMCAST, a disease forecasting system derived from FAST, (forecast system for Alternaria solani on tomato), appeared promising in managing purple spot disease on asparagus. The fungicides chlorothalonil and mancozeb are commonly used to protect the fern from purple spot but products with new active ingredients are needed to maximise control.

Newer fungicides and disease forecaster TOMCAST

A greenhouse evaluation of biorationals and a fungicide plus a field evaluation of fungicides for control of Fusarium crown and root rot on seedlings were conducted by B.R. Harlan and M.K. Hausbeck from the Department of Plant, Soil and Microbial Sciences of the Michigan State University. An evaluation of fungicides for control of purple spot on the fern was also conducted. For the greenhouse evaluation, disease development was moderate with the untreated inoculated plants. Industry standard fludioxonil (Cannonball WP) was the only treatment that resulted in statistically healthier crowns compared to the untreated inoculated control. The field evaluation of fungicide for control of Fusarium root rot on seedlings is shown in Table 2, and the evaluation of fungicides for control of purple spot on the fern is shown in Table 3. It indicates that fungicides can limit disease caused by soilborne and foliar pathogens. The fungicides that were of primary interest include fludioxonil (Cannonball WP) applied as a drench to seedlings for control of Fusarium crown and root rot or as a premix of pydiflumetofen + fludioxonil (Miravis Prime SC) for purple spot foliar disease. Currently, these fungicides are not registered for use on asparagus seedlings or fern in the United States but could fill an important void in disease management. Fungicides containing chlorothalonil (Bravo WeatherStik SC) or mancozeb (Roper), “would be good candidates for use in an overall program that includes pydiflumetofen + fludioxonil (Miravis Prime SC),” the researchers said, later adding that they “can be used in conjunction with the disease forecaster TOMCAST to provide long lasting protection.” They also said that, “The asparagus crown nursery offers a unique opportunity to protect the developing crown from disease to ensure that plant propagules used to establish production fields are as healthy as possible.”

Suppression of Fusarium with nano micronutrients

Past work with chloride salts has shown that fertility is very important in delaying the effects of decline due to FCRR. A strong positive association was noted between chloride applications, micronutrient (Cu and Mn) uptake and disease suppression. In Quebec, scientists concluded that Fusarium abundance was negatively associated with Cu and that declining fields had reduced levels of Mn. More recently, B and Mn deficiency has been associated with asparagus decline. Applying micronutrients in nanoscale may offer a novel approach to deliver these elements to asparagus roots. The oxide forms are relatively non-toxic when compared to the ionic salts. The large surface areas allow for enhanced dissolution and their extremely small size, these particles can enter and move within plant tissues for intra-plant transport. Split root pot culture was used in the greenhouse assays to test the efficacy of nanoscale micronutrients such as B (500 nm), CuO (40 nm), MnO (30 nm), MoO (100 nm), and ZnO (10-30 nm). Field studies were also conducted and research plots were established in sites that had previously been planted to asparagus.

Cu and Mn associated with plant health

The first preliminary greenhouse study conducted by W.H. Elmer, N. Zuverza-Mena and J.C. White from the Connecticut Agricultural Experiment Station screened B, CuO, MnO, MoO, and ZnO in split root pots and assessed the disease severity (% root lesions) on the exposed and non-exposed sides. Inoculation with F. oxysporum f. sp. asparagi resulted in root lesions over 58-60% of the root system, but when plants were treated with CuO and MnO, the exposed and non-exposed root sides had significant reductions. Nano-Cu reduced disease severity from an average 59% to 23% on the exposed side and from 59% to 30% on the non-exposed roots, demonstrating a systemic response, the researchers said. Similarly, nano MnO reduced disease severity from 59% to 16% on the exposed side and from 59% to 28% on the non-exposed roots. Molybdenum oxide reduced disease on the exposed side, but not on the non-exposed side, while nano Zn was ineffective on the exposed, but systemically reduced disease on the non-exposed side. B did not affect the disease severity. These findings agree with reports in the literature that Cu and Mn were positively associated with plant health.

One crown soak to increased yield

Although most nano micronutrients improved growth and suppressed disease, nano CuO and nano MnO were superior in the control split root studies. Nano CuO and nano MnO were not systemic in the plant but were retained in the exposed treated root only. However, both nano CuO and nano MnO promoted a systemic defence to infection and colonisation of FOA in non-exposed roots. Field studies were also conducted by the same scientists in Hamden and Griswold. Yields from 2020 and 2021 were combined. All of the yield variables showed the same trend so only marketable spear yield was presented. Yields in untreated plots in Hamden were the lowest, but soaking crowns with B, CuO. MnO, MoO or ZnO in 2018 led to 1.5-, 1.8-, 1.9-, 2.0-, or 1.3-fold respective increases in marketable yield. Responses were not as striking in Griswold, but notable differences were still evident. Increases of 35%, 32%, 23%, and 30% in the trimmed spear weights were observed for B, CuO, MnO and ZnO respectively. “The observations that a single crown soak treatment at planting could lead to increases in yield three years later is astonishing,” the researchers said. While fumigation and fungicide soaks/drenches have resulted in improved health during the first year, the suppression did not last and/or was cost prohibitive. In contrast, nano forms of micronutrients were effective in suppressing disease and increasing yield after three years.

Effect of flooding period on asparagus growth

Asparagus has been promoted as a paddy field conversion crop in Japan. However, converted paddy fields are prone to excessive soil moisture due to their low permeability and high-water retention. In previous research it has been reported that asparagus grown in such conditions had rotting underground stems and roots, resulting in reduced yields. Furthermore, in recent years, torrential rains have caused flooding of asparagus fields in Japan, affecting the growth and yield of asparagus. However, mitigation measures for flooded fields have not yet been established. Poor field drainage contributes to the development of soil diseases, such as wilt and blight. Fusarium oxysporum f. sp. asparagi, for example, is widely distributed in production fields and causes extensive damage to asparagus production. Although F. oxysporum has such a serious impact on asparagus cultivation, there’s been scarce research into its relationship with flooding. Therefore, a study was conducted by T. Sonoda from Rakuno Gakuen University, Japan to determine the effects of different periods of flooding and F. oxysporum f. sp. asparagi infection on asparagus growth in order to contribute to the improvement of asparagus cultivation methods in former rice paddies.

How flooding length affects growth

The first experiment studied the effect of flooding-period length on the growth of asparagus cultivars. The main asparagus cultivars used in Japan, ‘UC157’ and ‘Gijnlim’, were used as test cultivars. One month after sowing, their seeds were transplanted to PVC tubes filled with horticultural medium (photo) and grown in a glasshouse. Ten days after transplanting, when the roots had grown 20 cm, water was poured to the ground level to flood the asparagus seedlings. Flooding periods were 0, 1, 5, and 10 days. After the applicable flooding period, the plots were drained of excess water and thereafter irrigated in the same way as the control plots. Seedlings were then removed and their maximum grass height, number of stems, maximum root length, degree of root damage, aboveground dry matter weight and belowground dry matter weight were assessed. Root damage was determined by using a five-level index to identify root necrosis and rotting.

Root lengths tended to be shorter with increasing durations of flooding, but the extent of shortening did not vary between cultivars. The degree of root damage increased with increasing periods of flooding. Differences in grass height and above- and below-ground dry matter weight were observed between the cultivars, and no differences were observed between them during the different flooding periods. “No differences in stem and root number were observed between different periods of flooding or between cultivars. There was no interaction between the duration of flooding and cultivar type for any of the growth parameters,” the authors said.

The importance of drainage

Prolonged flooding seems to inhibit root growth. But even if a field was flooded, the impact on asparagus would be minimal if rapid drainage could be achieved. “These findings suggest that when asparagus is grown in paddy-conversion fields, it is important to construct ditch drain or underdrain in the field to quickly drain excess soil moisture and avoid prolonged flooding of the root zone,” the researchers wrote. They also said that If these measures are not sufficient, “it is necessary to implement cultivation with raised rows to ensure drainage and sufficient rooting area and to use water-tolerant cultivars.”

 

 

 

 

 

The second experiment studied the effect of infection with F. oxysporum f. sp. asparagi and flooding-period length on asparagus growth. Growing conditions and methods for this experiment were performed as described in the first experiment. F. oxysporum f. sp. asparagi was used for inoculation, which was isolated from asparagus production fields in Japan. Root damage observed on plants inoculated and flooded for 5 and 10 days was higher than plants inoculated and not flooded. Further, statistical test results indicate that there is an interaction between presence of fungus and duration of flooding. In F. oxysporum-inoculated areas, root length was significantly longer in the 0-day flooded area than in the 5- and 10-day flooded areas, and the degree of root damage increased as the flooding-period length increased. In the absence of F. oxysporum, there was no difference in root damage depending on the duration of flooding, while in the presence of F. oxysporum, the longer the duration of flooding, the greater the root damage. The results of this study suggest that disease development caused by F. oxysporum is accelerated by prolonged flooding. “Adding drainage measures to disease-resistant cultivars would reduce the impact of flooding and F. oxysporum f. sp. asparagi on asparagus growth,” the author said.

Sources:

Advancing control strategies for soil-borne and foliar pathogens in Michigan asparagus

B.R. Harlan and M.K. Hausbecka / Dept. of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI, USA.

Suppression of Fusarium crown and root rot of asparagus with nano micronutrients

W.H. Elmer1,a, N. Zuverza-Mena2 and J.C. White3 / 1The Department of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Station, 123 Huntington St New Haven CT, 06511, USA; 2The Department of Analytical Chemistry, The Connecticut Agricultural Experiment Station, 123 Huntington St New Haven CT, 06511, USA; 3The Connecticut Agricultural Experiment Station, 123 Huntington St New Haven CT, 06511, USA.

Effect of flooding period and infection with Fusarium oxysporum f. sp. asparagi on asparagus growth

T. Sonodaa / Rakuno Gakuen University, Midorimachi, Bunkyoudai, Ebetsushi, Hokkaido, Japan.

Growing vegetation coverage between the rows in asparagus plantations is a recent practice. It started with green asparagus crops to facilitate the passage of harvesting machinery and to limit soil compaction. The technique has also shown other advantages, too, such as the wind protection it offers for the asparagus to ensure a better-quality harvest and straighter spears. The many agronomic, thermal, ecological and environmental benefits afforded by vegetation coverage has now led to its use with white asparagus in several European production areas.

Benefiting from a “windbreak effect”

From an agronomical perspective, vegetation cover improves soil structure through the roots’ development of species in different soil horizons, thus enhancing the soil’s water capacity. The cover also protects against soil erosion. What’s more, growing species with taproots captures mineral elements such as nitrates in the deepest layers of the soil and limits leaching, while legumes bring nitrogen to the soil. Pulverising the foliage and root volume makes it possible to increase the soil’s humus content. The addition of organic matter significantly improves the soil’s microbial activity, thereby increasing the availability of nutrients. When a vegetation cover is maintained on a plot throughout the life of an asparagus plantation, the percentage of organic matter in the inter-rows is higher, rendering the plot more favourable for replanting, especially in asparagus groves with large spacing (more than 3.50m). It is worth considering applying vegetation coverage permanently in order to make the most of its thermal benefits throughout the crop cycle. In spring, when the vegetation cover develops above the mounds prior to harvest, this offers a “windbreak effect” that makes the plastics less likely to fly away or be removed. It also assists by warming the mound more quickly as it is less exposed to the wind, often from the north. An additional degree above 12°C at the crown can result in an additional 30 kg/ha harvested per day at the beginning of the asparagus season. Once it has been cut down in the first days of harvest, the vegetation cover can provide the soil with greater bearing capacity for the passage of harvesting machinery, especially during +rainy periods.

Planted, controlled and maintained

At the end of harvest, new plants develop, generating favourable conditions for the presence of auxiliary fauna (hoverflies, ground beetles, lacewings, ladybirds, etc.). They also limit the development of weeds in the inter-row. This is particularly useful when seeking to reduce the use of herbicides or for organic cultivation. After pulverising, the vegetation can be placed onto the planting row to provide a natural mulch that limits grass growth on the row. In autumn and winter, the cover can mitigate the effect of heavy rains. However, there can also be certain drawbacks to using soil cover, such as reduced aeration in the row and increased risk of disease due to higher humidity. Furthermore, in some situations, it can encourage the development of rodent populations.

The vegetation cover must be planted, controlled and maintained. It can be sown at the end of the harvest and benefit from the rains. At a later point, its installation will be easier if the plot is irrigated using a sprinkler system. It is recommended to combine different plant families, including grasses: rye, oats, and ryegrass (important root hair); cruciferous plants: fodder radish, Chinese radish, and white mustard (taproot); and legumes: Alexandria clover and fodder lentil (nitrogen fixation). The required duration of the vegetation cover (i.e., whether it is permanent or seasonal) also determines the choice of species. In this sense, it is necessary to take into account the plants’ sensitivity to frost. Oats, Alexandrian clover and phacelia are also sensitive to frost, whereas ryegrass, rye, lentil and radish are not very sensitive. Between 12 and 15kg/ha should be used depending on the planting distance and the width of the inter-row.

Improving plastics integration

Maintaining a permanent vegetation cover requires certain adaptations, and even material investment. Long planting distances allow for grassing of the row all year round while keeping enough soil available for the mounding. Some machinery manufacturers (e.g., Engels) have also adapted ridgers to maintain the grass cover of the row (see Equipment section). Even though grassing of the row requires repeated passages by a tractor and pulveriser to control the cover’s development (every 8-10 days with sprinkler irrigation or every 3 weeks with drip feed), fuel consumption is much lower than with tillage tools. Lastly, the “greening” of asparagus rows improves the integration of asparagus plots into the landscape and greatly reduces the “visual pollution” associated with asparagus that locals complain about in certain areas.

The initial establishment of an asparagus plantation deserves special attention because its later technical and economic success depends upon it. And this is particularly the case when asparagus is being replanted in a field where it has previously been grown. The development of rotary spaders (Farmax and Imants), however, has provided a way to facilitate the establishment of an asparagus crop. Preparing the soil to a depth of up to 1.1 m allows the creation of a homogeneous zone which favours the plant’s growth. The addition of soil conditioners and fertilisers makes it possible to harness the “soilless cultivation – in the soil” approach developed by Christian Befve&Co. This involves taking the following steps before planting the crop.

1. A soil study starting with a physical and chemical analysis of the soil structure at two levels: the surface layer (to a depth of 30 cm) and the subsoil (from a depth of 50 cm). (See image 1.) A visual soil evaluation via the “profil cultural” method is necessary. The purpose of this profile is to determine if there are indications of life in the soil, such as the roots of previous crops. Their depth gives indications of possible areas of compaction, ground water level, differences in soil structures (sand, clay, gravel, etc.) -photo 2- The depth at which the deepest roots are located will determine the depth of the subsequent tillage.

 

 

 

 

 

2. A significant addition of organic matter – from 80-150 tons/hectare depending on the nature of the soil improver – improves the structure and fertility of the soil. Organic matter from local sources is recommended. Depending on what is available nearby, manure (from cows, horses, sheep or poultry), grape pomace or vegetable waste (rice husks, crushed palms) may be used. The application must be concentrated on the planting row as the rotary spader passes over it in order to provide the best possible conditions for the plant to grow. (See images 3 and 4.) The addition of microorganisms (e.g. Bacillus and Trichoderma) improves soil health and limits growth of pathogenic fungi (e.g. Fusarium sp., Rhizoctonia).

 

 

 

3. Tillage creates a favourable area for root development by creating a larger volume of soil than would otherwise be available. This can be achieved with hand tools, as in Madagascar (image 5), or via use of tillage machinery (images 6 and 7). In either case, the roots are able to extend abundantly throughout the area that has been tilled.

 

 

 

 

4. Observation of the roots in both areas, under tillage as well as the no-till soil, clearly shows the benefits of deep tillage (namely use of a rotary spader). In the tilled soil, the roots are numerous, white with large fibrous rootlets (left). In the no-till area, the roots are brown, soil fungus is present and there are only a few rootlets (right).

 

 

 

 

5. Tillage provides long-term benefits for an asparagus farm. In this comparative table based on the average yield of 14 asparagus plantations in 5 different countries, it can be seen that soil prepared with a rotary spader delivers higher yields than no-till soil from the very first harvest and the maximum potential continues to increase each year for the first six years. In contrast, without use of a rotary spader, the yield is lower and potential peaks in the 5th year. Over the years, the production potential is always greater with the spader and there is greater longevity (+2 years). In total, over the lifespan of the asparagus farm, this soil preparation technique delivers a 50% higher yield than no-till.

6. The increase in the volume of loose, healthy and fertile soil is the key to this greater yield thanks to its promotion of root development. Observations 4 months after planting indicate that the root systems in a soil tilled by a rotary spader have 30% more roots per plant, with a depth of establishment twice as great, and a vertical orientation. This establishment slows the usual rise of the root system level to 0.5 cm per year instead of 3 cm, and thus keeps it to just 5 cm after 10 years instead of 30 cm. As a result, the crop is productive for longer.

As stated in the article “Productivity of a trial of thirteen asparagus genotypes in their eighth year”, the correct choice of genotypes to cultivate in a certain region is one of the main factors affecting later productivity. Because asparagus is a crop that presents marked genotype-environment interaction, it is necessary to evaluate the behaviour of different hybrids over various years in target production areas in order to determine which ones truly are the best adapted to the local agricultural and climatic conditions, especially when it comes to rainfed plantations. For this reason, the aim of the trial was to evaluate the performance of the 13 genotypes chosen once they had reached their stable productive stage – eighth harvest year.

Cultivars from Italy, China and the US used in trial

The thirteen all male hybrids chosen for the experiment were from three different countries: Italy, China and the United States. The six Italian green genotypes, obtained from the CRA (Center for Agricultural Research) in Lodi, were ‘IÍtalo’, ‘Vittorio’, ‘Eros’, ‘Ercole’, ‘Giove’ and ‘Franco’. From China came ‘Chino’ and from the United States the following six cultivars: ‘Early-California’, ‘UC 157’, ‘Patron’, ‘NJ-1189’, ‘NJ-1123’ (green) and ‘NJ-1192’ (a purple tetraploid). The experiment was initiated on November 16, 2011, close to the city of Azul in the centre of the Province of Buenos Aires, Argentina, in the Experimental Field (36°48’S, 59°51’W) of the Faculty of Agronomy, National University of the Centre of the Province de Buenos Aires (UNCPBA). Seedlings of 120 cm3 were planted in a random complete block design with four repetitions and at a density of 23,810 plants per hectare (1.4 m between rows and 0.3 m between plants within rows). Before planting, the experimental area was prepared with several applications of a disc plough and two of a cross chisel, and days before planting the discs were reapplied, followed by a tiller. The rows were marked with a furrow opener to a depth of 0.25 m.

Combined system used to control weeds

The experiment’s planted area was kept free of weeds via a combined system involving use of a motocultivator, manual removal and chemical control. Prior to plantation, Trifluralina was applied at 2 L/ha and in subsequent years a mixture of 0.5 kg/ha of 35% Metribuzı́n (C8H14N4OS) and 2.5 L/ha of 31.7% Pendimetalı́n (C13H19N3O4) (from the second year), in pre-emergence. In post-emergence, the following were applied as necessary: Glyphosate (C3H8NO5P) and Bentazon (C10H12N2O3S), in the areas affected by Cyperus rotundus; among other species.

The plants were rain-fed alone upon reaching stable production

Where needed, supplementary drip irrigation was applied weekly during the first few years after planting. Once a stable productive stage was reached the plants were solely rain-fed. Fertiliser was applied at the base in bands of 0.3 m with diammonium phosphate ((NH4)2HPO4) at 250 kg ha-1, and broadcast application of urea (CH4N2O) took place once a year during the vegetative phase, with dosage varying according to the point in the crop cycle. On November 28, 2018, the biological fertiliser Arco-Plus, of Mycophos (1 L ha-1) was applied, composed of macronutrients (4.6; 1.2 and 7% NPK, respectively); 14 micronutrients and vegetable hormones.

Harvesting took place every other day

From September 18 to November 12, 2019, spears were harvested – cut with knives at soil level – every second day, making for 27 days of harvesting in total. The harvest started when the spears were at least 23 cm long and had compact heads, which is the parameter denoting commercial maturity under the applicable quality protocol* in Argentina. All spears produced were harvested, even if destined as waste, so that the remaining spears could develop. Once harvested, the spears were taken to the Processing Laboratory of Horticulture of the Faculty of Agronomy, UNCPBA, for washing and post-harvest processes including grading. This transport took place as soon as possible after harvesting in order to preserve the organoleptic properties of the spears.

‘NJ-11232’ stood out as the strongest performer in commercial spear numbers

The researchers said that in the stable productivity stage of the trial (eighth harvest year), five male green asparagus genotypes of Italian origin (‘Franco’, ‘Giove’, ‘IÍtalo’, ‘Eros’ and ‘Vittorio’) and two genotypes of North American origin (‘NJ-1123’ (green) and ‘NJ-1192’ (purple tetraploid) demonstrated their productive superiority in tons per hectare for the central zone of the Province of Buenos Aires. In terms of the number of spears suitable for marketing, the North American genotype ‘NJ-1123’ delivered the best result. Although it also had the highest proportion of discarded and number two grade spears, it maintained its status as one of the best performers for commercial spear numbers, they said. (‘NJ-1123’ actually stood out for its productivity in each size not just in the eighth year of the trial but from the start of the plantation’s productive life.) Next after ‘NJ-1123’ in terms of total number of spears in the eighth year came ‘Giove’, ‘Ercole’, ‘Eros’ and ‘Early California’. For the largest spear diameters, ‘Eros’ and ‘Giove’ were the most productive genotypes, while for the smallest spear diameters it was ‘Early-California’ and ‘UC-157’.

Many more spears in 8th year vs. early productive years

In their conclusions in the paper, the researchers said that, as would be expected, the plantation productively evolved over the years and produced many more spears in the eighth year compared to the early productive years. They remarked that the percentage of discarded spears was high, “indicating that efforts to improve management practices during harvest should result in increases in commercial productivity.” (Earlier in the paper, they said the high discard rate was possibly due to the frequency of harvest being every other day, rather than every day.) Observing that there were notable differences in the ranking of the genotypes for productivity and spear number between the eighth productive year (reported in the paper) and earlier years of the plantation, they said, “It would seem that some genotypes require several years of growth before their adaptation to a certain geographic zone becomes apparent.”

Main source:

Castagnino, A.M., Diaz, K.E., Rosini, M.B., Benson, S., Bastien, E., García-Franco, A. and Rogers, W.J. (2023). Productivity of a trial of thirteen asparagus genotypes in their eighth year within the IV International Asparagus Cultivar Trial (ISHS). Acta Hortic. 1376, 81-88

DOI: 10.17660/ActaHortic.2023.1376.13