Techniques and Precautions of Sod Culture in Citrus Orchards in Sichuan Province

Ling LIN, Wei SONG

Neijiang Academy of Agricultural Sciences, Neijiang 641000, China

Abstract Citrus is an important fruit in Sichuan, accounting for 52.6% fruit yield of the whole Sichuan Province. In recent years, citrus has expanded its original cultivation and planting area in Sichuan, and the planting area has continued to increase. In terms of citrus cultivation methods, the sod culture has become a hot spot. This paper focused on the benefits of sod culture in citrus orchards, the selection of grass species, and the cultivation techniques. It analyzed the problems that should be paid attention to in sod culture in citrus orchards, in order to provide a theoretical basis for production and cultivation of fruit farmers.

Key words Sichuan citrus, Sod culture, Cultivation techniques, Precautions

1 Introduction

Citrus is an important fruit in Sichuan Province, accounting for 52.6% fruit yield of the whole province. According to the data of the Ministry of Agriculture of China in 2014, the total planting area of citrus in Sichuan was about 266 700 ha, and the yield was about 2.54 million t. Citrus planting is mainly distributed in the Chengdu Plain and eastern Sichuan. In terms of citrus planting area, Meishan, Guang’an, Ziyang, and Nanchong were more concentrated, followed by Chengdu, Suining, Neijiang, Leshan, and Dazhou. In terms of the citrus yield, Meishan, Ziyang, and Chengdu ranked first. The main cultivars included miscellaneous citrus (Buzhihuo, Chunjian, Aiyuan, Huangguogan); loose-skinned citrus (ponkan, Wenzhou tangerine); oranges (navel orange, blood orange); pomelo (Shatian pomelo, Longan pomelo, honey pomelo) and lemons.

In recent years, Sichuan citrus has expanded its original cultivation and planting area, and the planting area has continued to increase, forming many characteristic citrus industrial belts, such as Danleng Shiranui, Linshui Navel Orange, Zizhong Blood Orange, and Anyue Lemon,etc.In addition, in order to realize the labor-saving cultivation of citrus and improve the comprehensive economic benefits of citrus, Sichuan citrus orchards began to implement a large number of sod culture model. In view of this, we put forward some views on the technology and precautions of citrus sod culture model.

2 Concept of sod culture

The citrus orchard sod culture is a mode of planting a certain amount of legumes, gramineous plants, pastures or natural grasses between rows or plants of citrus, combined with proper fertilization, irrigation and other technical management, cutting grasses when they grow to 30 cm in stages, drying in the sun until half-dried, buried under the tree tray, and repeated every year.

3 Benefits of sod culture

3.1IncreasingthesoilorganicmattercontentAfter growing grasses in orchards, the secretions and residual roots of the grass roots promote the microbial activities and contribute to the formation of the root soil aggregate structure; after the grass is overturned and decomposed, it becomes good organic matter. Studies have shown that the content of soil organic carbon, composite organic carbon, loose-tight humus, and active organic carbon in sod culture mode significantly increased, and the tightness ratio increased significantly[1]. Studies have also confirmed that after growing grasses in citrus orchards, it can increase the content of N, P, and K available nutrients in the soil and improve the growth of citrus. In an orchard with a thickness of 30 cm and a soil organic matter content of 0.5%-0.7%, the content of soil organic matter can be increased to 1.6%-2.0% after 5 consecutive years of plantingDactylisglomerataL. andTrifoliumrepens(white clover)[2].

3.2ImprovingsoilstoragecapacityAfter growing grasses in citrus orchards, the soil organic matter increases, the aggregate structure is formed, the effective porosity of the soil increases, and the soil water-holding capacity also increases. It can reduce soil moisture when there is too much rainfall, but can maintain soil moisture when there is too little rainfall. In addition, after growing grasses, the ground temperature can be increased by 2-3 ℃ in winter and 3-6 ℃ in summer, so that the orchard soil has low evaporation and low water demand, thereby improving soil storage capacity.

3.3ImprovingfruitqualityandincreasingfruityieldAfter growing grasses in orchards, the soil organic matter is increased, and the soil nutrients are more sufficient and balanced, which is conducive to strengthening the tree body and improving the fruit quality. An experiment has shown that whenPaspalumnatatu(Bahiasgrass) was planted in citrus orchard, the fruit setting rate of citrus increased from 1.58% to 1.81%, the fruit yield increased by 13.1%, the soluble solid content increased by 7.6 g/kg, and the citric acid content decreased by 0.9 g/kg, both fruit quality and yield were significantly improved[3]. The research of Ren Qunetal.[4]also indicated that sod culture can effectively increase the content of potassium, phosphorus and boron in citrus leaves and the sugar-acid ratio of fruits.

3.4ImprovingorchardecologicalenvironmentThe sod culture in citrus orchards increases vegetation coverage and provides favorable conditions for the reproduction of microorganisms. Many beneficial microorganisms such as nitrogen-fixing bacteria and soil arbuscular mycorrhizal fungi are produced in large quantities, which promote the absorption and utilization of citrus roots to N, P and other nutrients. After growing grasses, it creates suitable living conditions for the natural enemies of pests, which is conducive to the comprehensive control of citrus pests and diseases, thereby reducing the input of pesticides and the pollution of pesticides to the environment and fruits.

3.5SavinglaborandreducingcostsIn the management of citrus orchard, manual weeding requires a lot of labor. The practice of growing grasses in orchards can not only improve soil fertility, but also save labor for soil plowing and weeding, and reduce the use of chemical fertilizers. At the same time, the content of organic matter in the soil increases, the tree vigor is stronger, it can resist various pests and natural disasters, and it can also reduce the cost of the orchard; the sod culture in the orchard is also conducive to the promotion of mechanized operations in citrus orchard.

4 Selection of grass species in citrus orchard

For the sod culture in citrus orchards, it is very important to choose good grass species. It is necessary to pay attention to the following points: (i) the grass is perennial; (ii) the root system is mainly shallow; (iii) the plant is low and the mulching effect is good; (iv) good drought and cold resistance, relatively shade-tolerant, trampling-resistant, and easy to manage; (v) there is no common disease with fruit trees, and it is not a parasitic or resident site for fruit tree pests and pathogens; (vi) the species has a certain amount of grass production and other economic benefits[5]. Common grass species for sod culture includes white clover,LoliumperenneL.,MedicagosativaL.,ViciasativaL., Bahiasgrass, andVulpiamyurosL. Specifically, white clover is a perennial leguminous plant with strong nitrogen fixation ability, shallow root system, trampling resistance, shade tolerance, high fertilizer efficiency, no competition with fruit trees for fertilizer, dense grass layer, and high ornamental value;V.myuroshas strong adaptability, moderate yield, can inhibit the growth of weeds, germinate and grow naturally, wither and die naturally, without manual mowing. These two grass species became the grass species with the highest evaluation of growing grass for sod culture in citrus orchards.

5 Sod culture techniques for citrus orchard

5.1SowingofgrowinggrassesforsodcultureSowing time is divided into spring sowing and autumn sowing. Spring sowing is generally implemented from late March to April, and autumn sowing can be conducted from mid-August to mid-September. Before sowing, it is necessary to plow the rows of fruit trees 20-25 cm deep, level them, conduct proper irrigation, and sow them when the moisture is suitable. The sowing method can be furrow sowing or broadcast sowing. For the furrow sowing, the furrows are first opened, and the seeds are covered with soil; in the broadcast sowing, the seeds are first planted, and then a layer of dry soil is evenly spread on the seeds.

5.2SeedlingmanagementAfter emergence of seedlings, it is necessary to conduct irrigation according to moisture content. If the emergence of seedlings is not neat, it is necessary to replenish the seedlings in time. Some nitrogen fertilizers can be applied with the water, or sprinkled or sprayed on the leaves when it rains. In addition, it is necessary to remove weeds in time, and pay special attention to remove those vicious weeds that are easy to grow tall.

5.3MowingAfter a few months of growing grasses in the orchard, it is necessary to mow when the grass height is more than 30 cm. Mow 2-4 times in a growing season, and use the cut grass for mulching the tree tray. This can not only control the height of the grass, but also promote the tillering and branching of the grass, and improve the coverage and yield. The grass that grows in autumn is no longer mowed, it is necessary to use them for mulching in winter.

6 Precautions for sod culture in citrus orchard

6.1SelectingappropriategrassspeciesDifferent regions have different climatic conditions and soil conditions. It is recommended to select the appropriate grass species according to the local conditions. In arid areas, grass species with good drought resistance can be used, such asLotuscorniculatusL,Astragalusmembranaceus; in humid and shaded areas, white clover, Bahiasgrass, and peppermint can be used.

6.2SelectingappropriatesowingmethodGenerally, orchards at young-tree stage only grow grass between the rows of trees, and the distance between the grass belt and the outer edge of the tree tray is about 40 cm. Orchards at mature-tree stage can grow grass between the rows and between the plants, and no grass can be grown under the tree tray to prevent pests from damaging the trunk.

6.3StrengtheningfertilizerandwatermanagementatseedlingstageMany fruit farmers sow grass seeds into the soil and think that grass seeds can grow well naturally, so they just ignore them, neither applying fertilizers nor watering. As a result, the growth of grass in the orchard is not good. In practice, to make grass grow well, it is required to strengthen fertilization and irrigation, apply enough base fertilizer before sowing, apply seedling fertilizer at the seedling stage, and water in time when it is dry.

6.4RemovingweedsWeeds can be cleaned up by combining artificial weeding and chemical weeding[6]. Before growing grasses, it is necessary to clean up the weeds around the orchard, and if necessary, use herbicides to treat the weeds. The farmyard manure applied should also be decomposed at high temperature to kill weed seeds. In the initial stage of grass growth, the growth of the planted grass seeds may not be as good as that of weeds. Therefore, it is required to remove weeds, especially vicious weeds, such asPraxelisclematidea,Phragmitescommunis,Commelinadiffusa,Cyperusrotundus, andXanthiumsibiricum,etc.

6.5StressingthepreventionandcontrolofdiseasesandinsectpestsAfter implementing the sold culture, the growth of the grass provides a favorable environment for the growth of underground pests, resulting in the increase of underground pests to varying degrees. Therefore, it is necessary to stress the prevention and control of diseases and insect pests.

6.6RenewingandmowinggrassesAt the early months of growing grasses, do not mow. Do not start mowing until the grass plant grows to more than 30 cm. When mowing the grass, do not cut it all at once. Leave a part of the grass along the row for the next mowing, and repeat this process, so as to leave the living space for natural enemies. After a certain period of growing grasses (generally 3-5 years), when the grass layer begins to age, it should be turned over in time to turn the surface organic matter into the soil and renew the grass seeds.