Key points of pollution-free asparagus cultivation techniques in northern Zhejiang

Pollution-free asparagus cultivation measures in northern Zhejiang

Northern Zhejiang is close to Shanghai, Suzhou, Hangzhou and other areas along the Yangtze River Delta, so the asparagus grown there has a broad sales market. In addition, asparagus can promote human digestion, enhance appetite, and has high health value. In northern Zhejiang, asparagus yield is 1 000-1 400 kg/667 sq m, and income is 6 000-8 000 yuan/667 sq m, which provides farmers with new ideas and new directions for planting, while also improving the agricultural industry chain.

1 Variety selection

Seed selection is the foundation of high-yield asparagus. Selecting high-quality, high-yield, disease- and pest-resistant asparagus varieties can not only increase asparagus planting yield, but also reduce diseases and pests and improve product quality. Summarizing the experience of experimental demonstrations in recent years, varieties such as Grant and 308 can be selected. They show early sprouting, fast growth speed, evenly thick rhizomes, tightly packed head scales that do not easily scatter, full and deep green color, good commercial performance, and high output value. In addition, their growing plants are dwarf type, resistant to diseases and pests and resistant to lodging, and belong to dual-purpose varieties for both green and white asparagus, making them relatively ideal production varieties at the present stage.

2 Optimizing cultivation models

2.1 Rain-shelter cultivation in greenhouses

Stem blight is a common disease of asparagus and can lead to asparagus death in severe cases. The original pathogen of this disease is the fungus Phomopsis of the Deuteromycotina, which mainly affects the stem and branch parts of asparagus. The pathogen overwinters in the field where the plants grow as pycnidia, and conidia are produced in the following spring, with 20-30 °C being the most suitable temperature for germination. The plum rain season, with higher temperatures and greater humidity, is the best stage for disease occurrence and spread. Using greenhouses for rain-shelter cultivation can block the transmission channels of water molecules.

2.2 Ridge cultivation

This cultivation method avoids the impact of field water accumulation on asparagus. Normally, a length of 6 m, a width of 145 cm, and 4 ridges are suitable, with deep operation trenches and drainage ditches dug to a depth of 25 cm between ridges. When transplanting, plant the seedlings in the middle of the ridge surface, with a spacing of 30-35 cm per plant.

2.3 Micro drip irrigation system

Limited by asparagus cultivation conditions, a good drainage and irrigation system must be set up in asparagus fields, so that irrigation operations can be carried out under different conditions as much as possible and planting conditions can be met. Among these, a micro drip irrigation system can gradually infiltrate water into the soil, reduce the water evaporation rate and infiltration rate, help solve the high-humidity environment problem caused under traditional irrigation conditions, is not conducive to water retention and absorption, and avoids phenomena such as high disease incidence and loss of fertilizer and water.

3 Pre-sowing preparation

3.1 Sowing

24-48 h before sowing, fill the nutrient soil in the nutrient pots in advance, water thoroughly, then cover with plastic film and press it down tightly so that the nutrient soil is fully soaked for breeding [2]. On the day of sowing, uncover the film, use a medium-sized small stick to make small holes 1 cm deep, place the seeds in the small holes during sowing, cover with 1 cm of nutrient soil after sowing, and cover with film again the next day after sowing. If it is summer, spread grass mats or rice straw over the film. After completing this series of steps, set up an arched shed, and add shading facilities above to prevent rain

water from washing it away.

3.2 Seedling stage management

First, temperature. From completion of sowing to the seedling emergence stage, the temperature in the pot soil must not be higher than 30 °C; after emergence, 20-28 °C is optimal. Second, humidity. In the early stage, irrigation should be relatively moist; after full emergence, alternate dry and wet according to water needs; after the growth height reaches 10 cm, keep it mainly dry. Finally, cultivation site treatment. Asparagus is suitable for growing in sandy soil with deep and loose soil layers, rich organic matter, low groundwater level, good drainage and irrigation performance, and suitable acidity and alkalinity. However, the soil in northern Zhejiang is generally severely clayey. Therefore, in order to meet asparagus cultivation conditions, organic matter with heavier fiber, namely mushroom spent substrate, is selected as a soil improver to improve the relatively heavy clayey condition of local soil [Jishan Huayao].

4 Field management

4.1 Planting

Generally, planting can be carried out when there are about 5 small shoots. For planting, select robust seedlings and plant them in furrows according to grade, with a spacing of 30-35 cm per plant. Spread the transplanted plants evenly on the soil surface, cover and press them tightly, and after the roots and soil are closely attached, evenly mix 1 000.0 kg of clear water, add 40% manure material and 0.2 kg of asparagus green, shake evenly, apply in the planting furrow, and cover with 5-6 cm of loose soil, in a turtle-back shape [3]. It should be noted that the scale buds on the underground stems of the seedlings should be arranged and planted in a fixed direction, with the tender buds concentrated in the central position and distributed evenly, so as to improve asparagus yield and quality.

4.2 Fertilization management

Asparagus is a perennial crop, and planting years and management levels differ, resulting in large yield differences. Therefore, according to actual soil fertility, yield level, and other factors, fully consider asparagus demand for fertilizer and determine scientific fertilization amounts, so as to improve yield and quality. For mature asparagus, when the normal yield per 667 sq m is higher than 1 000.0 kg, apply 27.2 kg of nitrogen fertilizer, 17.5 kg of phosphorus fertilizer, and 23.75 kg of potassium fertilizer. Referring to the different characteristics of asparagus at different growth and development stages, focus fertilization 3 times each year.

4.3 Watering management

Irrigation is the most important link, controlling the growth needs of stems and leaves, and ensuring good growth of young stems through timely drainage. After autumn, irrigate once about every 10 d to ensure healthy growth of stems and leaves and prolong the time for nutrient accumulation. Irrigate once with wintering water before the soil freezes. Pruning of stems and branches should also be reasonable, avoiding the impact of diseases and pests and reducing water evaporation.

4.4 Retaining mother shoots and thinning plants for trellising

4.4.1 Retaining spring mother stems. Retaining spring mother stems is related to the success of high yield in summer shoots. The time for retaining spring mother stems generally depends on the actual yield of spring shoot growth that year and the quality of shoot age. Normally it is from early April to late April, and the time just after rain when it first clears is the best time to retain mother stems for spring shoots. For two-year-old asparagus, retain about 3; for three-year-old asparagus, retain about 4; for four-year-old and above asparagus, retain about 5, with a maximum of no more than 8. Select robust tender shoots to retain. After retaining mother stems, promptly remove weak branches, residual branches, diseased branches, and weeds, and top them when the stake height is 1.5 m.

4.4.2 Retaining autumn mother stems. Raise enough autumn mother stems and fully store nutrients to lay a high-quality foundation for next year's spring shoot cultivation. The time for retaining autumn mother stems generally starts in early August. Normally retain 6-8 plants per plant (crown) evenly, distributed scatteredly. Because autumn mother stems are numerous and vigorous, promptly clean up and prune, remove thin, weak, and diseased branches and weeds, so as to facilitate ventilation and light transmission and reduce the incidence of diseases and pests. To avoid lodging caused by typhoons, promptly complete topping and staking work, and set up trellises with double lines.

5 Disease and pest control

5.1 Stem blight

It generally occurs on the main stem section 30 cm from the ground, with infiltrative brown small spots appearing at intervals, later gradually developing into blue-gray or gray-brown, and simultaneously expanding into diamond shapes, with many lesions connecting into strips. Around the lesions, the edges are reddish brown, and the sunken middle areas are gray-brown, densely distributed with pointed small spots. For control of this type of disease, first choose higher, dry, drainage-favorable plots for planting. Second, thoroughly clean the field, remove diseased stems, then burn or bury them; when fertilizing, control the amount of nitrogen fertilizer to prevent excessively vigorous growth. During routine management and control, pay close attention and observe. Once this type of disease is found, in the early stage of disease occurrence use certain proportions of thiophanate-methyl solution, Bordeaux mixture, and zineb solution, spraying once every 7 d, continuously spraying two or three times.

5.2 Rust, root rot, and sclerotinia rot

The occurrence of rust affects cultivation results. Therefore, diseased stems need to be thoroughly burned, and branch thinning and topping should be carried out in a timely manner to improve field ventilation and light transmission conditions and reduce field humidity. In the early stage of disease occurrence, use chlorothalonil solution and folpet for control. Root rot starts rotting from the local cortex of the stem, and the roots are also affected by this, causing the main stem to rot [4], and finally aging. During the seedling planting stage, soak the roots with benomyl for 15 min. Sclerotinia rot mostly occurs when young stems grow near the ground. First, discoloration appears and gradually turns brown, and finally black sclerotia like mouse droppings are produced. The control method is similar to that for stem blight.

5.3 Insect pests

These include grubs, mole crickets, bean seed flies, wireworms, and many other types. You can make 25% trichlorfon powder and 5 times fine soil into poisonous soil and apply it in the field, or spray 80% dichlorvos emulsifiable concentrate solution while fertilizing.

6 Harvesting

Harvest time needs to be effectively adjusted according to market demand. When harvesting, use your hands to break off and pull up asparagus together with the underground rhizome part, or use a sharp knife to cut flat at 2 cm below the ground. The harvest period is mainly concentrated in spring and summer, and the time can be divided into 2 sessions, morning and afternoon. Harvesting usually begins in early April and ends when the average quality of shoots decreases significantly. Spring mother stems begin to be retained in late March before harvesting, and the retention period for autumn mother stems begins in early August.

Three to four years after planting, it enters the harvest period, and the harvest period is generally two to three months. Green asparagus can be harvested when the young stems grow to 25 cm; the harvest standard for white asparagus young stems is somewhat lower, usually harvested at about 18 cm. In addition, according to the quality pricing requirements of products on the market, they must be picked only when they grow 20-24 cm above the ground, and harvested at 2 cm below the soil, then graded and sold together.