Fertilizer Requirements of Kiwifruit and High-Yield Fertilization Techniques and Timing

Kiwifruit originated in the Xiangxi region of Hunan Province, China, and Shaanxi at the northern foot of the Qinling Mountains is the region with the richest kiwifruit resources in China. So what are the fertilizer requirements of kiwifruit and the high-yield fertilization techniques and timing? For every 1000 kg of fresh fruit produced, kiwifruit needs to absorb 1.8 kg of nitrogen, 0.2 kg of phosphorus, 3.2 kg of potassium, 0.45 kg of calcium, 1.6 kg of magnesium and 0.2 kg of sulfur. The absorption of nitrogen, phosphorus and potassium occurs from the rapid leaf growth stage to the fruit set stage, mainly from the nutrients stored in the tree from the previous year, with relatively little absorbed from the soil; during the fruit development stage, the amount of nutrient absorption increases significantly, especially the absorption of phosphorus and potassium; before leaf fall, a certain amount of nutrients is still absorbed and stored in the tree to provide nutrients for budding, leaf expansion and flowering the following year.

Kiwifruit High-Yield Fertilization Techniques

Kiwifruit is fertilized three times a year. The first is base fertilizer, generally applied after fruit harvest, mainly organic fertilizer, supplemented with compound fertilizer, accounting for 50% of the annual fertilizer amount, to restore tree vigor and store nutrients for the next year's growth. The second is spring fertilizer, applied before spring buds sprout, to supplement the nutrients needed for flower bud development and promote the growth of axillary buds and new shoots. The third is summer fertilizer, applied during the fruit enlargement stage, to promote rapid fruit enlargement and new shoot growth. Spring fertilizer accounts for 20% of the annual amount, and summer fertilizer accounts for 30%. The amount of fertilizer used for kiwifruit varies with tree age and soil conditions. For example, at 4 to 5 years of age, the application rate per 667 sq m is 6.0 to 8.0 kg of nitrogen, 4.0 to 6.4 kg of phosphorus and 4.7 to 7.3 kg of potassium. For adult trees, the fertilizer application rate per 667 sq m is: 13.3 kg of nitrogen, 10.0 kg of phosphorus and 12.0 kg of potassium. It should be pointed out here that kiwifruit is very sensitive to chloride ions, so chloride-containing fertilizers should be avoided as much as possible.

Growing Environment

Temperature

Temperature is the main factor limiting the distribution and growth of kiwifruit. Each species has a suitable temperature range, beyond which growth is poor or survival is impossible. Most kiwifruit species require a warm and humid climate, that is, a subtropical or temperate humid to semi-humid climate, and are mainly distributed in vast areas at 18 to 34 degrees north latitude, with an annual average temperature of about 11.3 to 16.9°C, an extreme maximum temperature of 42.6°C, an extreme minimum temperature of about -20.3°C, an effective accumulated temperature above 10°C of 4500 to 5200°C, and a frost-free period of 160 to 270 days.

The temperature requirements among kiwifruit populations are also not very consistent. For example, Actinidia chinensis grows and develops well at an annual average temperature of 4 to 20°C, while Actinidia deliciosa is most widely distributed within the range of 13 to 18°C. The growth and development stages of kiwifruit are also affected by temperature. Studies have shown that for Actinidia deliciosa, when the temperature rises to about 10°C, the young buds begin to sprout, flowering can only occur above 15°C, and fruiting can only occur above 20°C. When the temperature drops to about 12°C, it enters the leaf-fall dormancy period. The entire development process requires about 210 to 240 days, during which the daily temperature cannot be lower than 10 to 12°C.

Water

Kiwifruit needs water but is also afraid of waterlogging. It is a fruit tree with weak physiological drought tolerance and weak moisture tolerance. Therefore, it has relatively strict requirements for soil moisture and air humidity, which determines that kiwifruit is most suitable for cultivation in areas with abundant and evenly distributed rainfall, relatively high air humidity, and humidity without waterlogging. The natural distribution area of kiwifruit in China has an annual precipitation of 800 mm to 2200 mm and a relative air humidity of 74.3% to 85%. Generally speaking, areas with annual precipitation of 1000 mm to 2000 mm and relative air humidity of about 80% can all meet the water requirements for kiwifruit growth and development. If the annual average precipitation is 500 mm, irrigation facilities must be considered for irrigation during droughts. High mountain areas have more fog, and the soil on both sides of streams and ravines is moist with high humidity year-round, which is relatively ideal for kiwifruit growth. In the central and eastern regions, rainfall is sufficient from April to June, and shoot growth is large, which suits the growth requirements of kiwifruit.

Kiwifruit has weaker drought resistance than ordinary fruit trees. Kiwifruit leaves are large and dense, with high transpiration and a relatively large water demand. According to estimates, an adult kiwifruit tree with a canopy area of 25 sq m transpires and loses more than 75 liters of water per day. Generally, when the soil moisture content decreases to 5% to 6%, it leads to insufficient water, causing the growth of kiwifruit shoots to be hindered. Its leaves begin to suffer from drought, drooping and becoming smaller, and the leaf margins wither. During drought, the leaves begin to dry up, and at this time timely irrigation or water spraying is necessary, especially at the seedling stage when the root system has not yet fully spread, so sufficient water must be supplemented. In addition to not being drought-tolerant, kiwifruit is also afraid of waterlogging. When drainage is poor or waterlogged for 2 to 3 days, about 40% of the plants die. During the plum rain in southern China or the rainy season in the north, if it rains continuously and drainage is poor, the roots are in a flooded state, which affects root respiration. Over time, the root tissue rots and the plants die. Therefore, when planting, deep furrows and high beds should be used for cultivation, and the orchard should be equipped with a complete drainage and irrigation system.

Light

Most kiwifruit species prefer a semi-shaded environment. They like sunlight but are relatively sensitive to strong light. They are a moderately light-loving fruit tree species, requiring 1300—2600 hours of sunshine. They prefer diffused light and avoid direct strong light. Fruiting plants require a certain amount of light, and a natural light intensity of 42% to 45% is suitable.

Soil

The soil should preferably be deep, fertile, well-aerated sandy soil with a groundwater level below 1 m, high organic matter content and a slightly acidic pH of 5.5-6.5. Strongly acidic or alkaline soil needs to be improved before cultivation.

Altitude

Kiwifruit can generally be planted at 800-1800 m, but 1000-1600 m is more suitable.

Other Conditions

Kiwifruit has quite weak wind resistance and is susceptible to wind damage. The main reasons are that its leaves are large and lack elasticity. Strong winds break young tender branches, shatter leaves, and cause fruit to be rubbed, bruised or shaken off, thereby reducing yield and market quality. Therefore, when establishing an orchard in mountainous areas, try to avoid choosing windward openings, ridges and mountaintops with strong winds. It is suitable to choose leeward slopes, with slope aspects of early-sunny slopes and late-sunny slopes.