What are the respective effects of applying various fertilizers to navel oranges?
What effects do various fertilizers have on navel oranges? Please provide a detailed introduction. Like other citrus, navel oranges require an adequate supply of nutrients for growth and fruiting, and there are sixteen essential nutrient elements. According to the required amounts of mineral elements, they can be divided into macronutrients (nitrogen, phosphorus, potassium), secondary nutrients (calcium, magnesium, sulfur) and micronutrients...
What effects do various fertilizers have on navel oranges? Please provide a detailed introduction
Like other citrus, navel oranges require an adequate supply of nutrients for growth and fruiting, and there are sixteen essential nutrient elements. According to the required amounts of mineral elements, they can be divided into macronutrients (nitrogen, phosphorus, potassium), secondary nutrients (calcium, magnesium, sulfur) and micronutrients (boron, zinc, iron, copper, manganese, molybdenum). These nutrient elements each have important roles in the physiology of navel oranges, and the elements cannot substitute for one another.
Physiological functions of the elements and their effects on the tree
1. Nitrogen
Nitrogen is an important element that makes up living matter; it is a main component of amino acids, proteins, nucleic acids, enzymes and chloroplasts. It is also an extremely important element affecting the metabolic activity, growth and fruiting of navel orange plants, and it is also the element required in the largest amount. Many experimental studies have shown that within a certain range, as nitrogen increases, the growth and yield of navel orange plants increase, and the juice content, fruit acid and soluble solids all increase. When nitrogen is deficient, tree vigor weakens, branches are short and leaves are few; leaves are small and thin, and leaf color is dark green with a yellow tinge; flowers and fruits are few, and quality declines. When nitrogen is excessive, plants grow excessively, causing reduced resistance; flower bud differentiation is poor, physiological fruit drop is heavy, and young trees are delayed in entering the fruiting stage; the rind thickens, juice decreases, and both the solids and citric acid contents decline, giving a bland flavor. The relationship between the nitrogen content of spring shoot leaves at 5-7 months of leaf age and various characteristics in navel oranges is shown in the figure.
In navel orange plants, a large amount of nitrogen exists in organic form, with only very small amounts of ammonium nitrogen and nitrate nitrogen in the roots. For the whole plant, most of the nitrogen is present in the leaves, accounting for about 40% of the whole tree, with branches and trunk accounting for 30%, roots 10%, and fruit 20%. New shoots and flowers of navel oranges contain the most nitrogen, so spring shoot flushing and flower and fruit development consume relatively more nitrogen.
For the nitrogen nutritional status in mature navel orange trees, a nitrogen content of 2.4-2.6% in the leaves of spring shoot vegetative branches is the moderate nitrogen level. In normal fruiting trees in California, USA, for every 50 kg of fruit produced, 0.2-0.25 kg of nitrogen needs to be absorbed, and about 20-23.3 kg of pure nitrogen is applied per mu (37 trees planted per mu), equivalent to 43.5-50.5 kg of urea (1.18-1.36 kg per tree) or 117.5-137.5 kg of ammonium bicarbonate (about 3.18-3.72 kg per tree).
According to leaf analysis, as the nitrogen content in leaves increases, the amount of nitrogen applied per tree decreases accordingly. For example, when the percentage of nitrogen in leaves is 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6 and above 2.7 respectively, the kilograms of pure nitrogen applied per tree are 1.35, 1.35, 1.15, 0.9, 0.7, 0.45, 0.25, 0.0 in that order.
2. Phosphorus
Phosphorus is a main component of the cell nucleus and cytoplasm, plays an important role in both the material metabolism and energy metabolism of cells, and is another essential important element. The distribution of phosphorus in the plant is similar to that of nitrogen, being most abundant in meristematic tissues. The flower organs, seeds, and actively dividing sites such as new shoot and new root growing points of navel oranges accumulate relatively large amounts of phosphorus.
The influence of phosphorus on navel oranges is most prominently reflected in fruit quality. An adequate phosphorus supply can promote root and new shoot growth and flower bud differentiation, increase the fruit-setting rate, and make the fruit ripen early with a thin rind and abundant juice, reducing acid and increasing sugar. When phosphorus is deficient, growth is poor, leaf drop occurs earlier, the quality of flower bud differentiation declines, the fruit texture is coarse, the rind is thick, and the acid content increases. When phosphorus is excessive, the harm to navel orange growth is also great: fruits become smaller, yield declines, and copper and zinc deficiency symptoms are simultaneously induced.
The total amount of phosphorus absorbed by navel orange roots is not large, and the utilization rate of phosphorus in the soil is not high and is also very slow. Therefore, the phosphorus status of the plant is often assessed mainly by leaf analysis. Soil analysis is also placed in a very important position, because soil analysis can reveal not only deficiency but also excess.
Phosphorus fertilizer application in navel orange orchards should be done with proper methods; if fertilization is improper, the plant will show phosphorus deficiency even though the soil has sufficient phosphorus. A necessary condition for increasing navel orange yield is that the phosphorus content of old spring shoot leaves must be greater than 0.1%. Generally, the standard for phosphorus in leaves is 0.12-0.16% of dry matter; below 0.12% indicates insufficient phosphorus, which will lead to a decline in yield. Especially when nitrogen fertilizer is increased, a corresponding increase in phosphorus fertilizer is more beneficial to growth and fruiting. Trees entering the full fruiting stage especially need an adequate phosphorus supplement; generally, for every 50 kg of fruit produced, 0.115 kg of phosphorus pentoxide (P2O5) needs to be applied, equivalent to 0.64 kg of calcium magnesium phosphate fertilizer.
3. Potassium
Although potassium is not a constituent substance of the organism, it is a necessary condition for its normal physiological activities. In navel orange plants, potassium exists in ionic form and is highly mobile, often moving from old leaves to vigorously metabolizing buds, young leaves and root tips, so it is closely related to cell division and growth. The flowers and fruits of navel oranges contain high levels of potassium, so it is also an important element determining fruit yield and quality.
An adequate potassium supply can promote the plant's assimilation, keeping shoot growth and tree vigor normal. Fruit setting and fruit development are good, fruits become larger and heavier, flavor is rich, fruit drop is reduced, and fruit storability is improved. It also enhances the plant's cold, drought and disease resistance. Navel oranges are prone to fruit cracking; an adequate application of potassium can increase cellulose and plays a positive role in improving the toughness of the rind, which can reduce fruit cracking. When potassium is insufficient, protein and fat synthesis is hindered, young shoots drop, lateral branches grow in clusters, and yellow spots similar to biuret poisoning appear at the leaf tips; physiological fruit drop is severe, fruits become smaller, the rind is thin and easily cracked, coloring occurs earlier, yield declines, and resistance weakens. When potassium is excessive, especially when the amounts of phosphorus and lime are insufficient, it leads to leaf hardening, large fruits with coarse rinds, increased acid, reduced solids content, and it also easily induces magnesium deficiency. The potassium uptake of fruiting navel orange trees is similar to that of nitrogen.
The suitable potassium content in leaves is 0.7-1.1% of dry matter. For adult navel orange trees producing 40-50 kg per tree, the annual application per tree is 0.115-0.225 kg of potassium oxide (K2O), equivalent to 0.225-0.45 kg of potassium sulfate.
4. Calcium
Calcium is an important component of cell wall pectin, keeping cells cohesive rather than dispersed. The calcium content in navel orange plants is higher than that of other elements, accounting for more than 50% of the ash. Most of it is present in branches and trunk, coarse roots and leaves. Calcium in the tree is immobile, so parts such as old leaves have a higher calcium content. The calcium content in fruit is second only to potassium, and the suitable calcium content in leaves is 3.0-4.5% of dry matter.
An adequate calcium supply can make the fruit surface smooth, the fruit plump, with less acid and a sweet taste, and early ripening and storability and transportability, similar to the effects of phosphorus. When the calcium content is below 3.0%, yield will increase as the calcium content increases. Within the adequate range, yield no longer increases, and at this point fruit quality is best. When it is below 1.5%, cell division is hindered; the root tips are the first to be damaged, growth stagnates, sensitivity to soil oxygen deficiency occurs, resistance is weak, and roots rot easily; the tips of young leaves turn yellow and die, the growing points of new shoots die, new shoots become shortened and clustered, and the color of the leaf midrib becomes lighter, resembling symptoms of iron and manganese deficiency; fruits are deformed and easily cracked, juice sacs shrink, and they are more acidic. In extreme calcium deficiency, leaves drop early, many branches die, and tree vigor declines severely. Calcium deficiency is less commonly seen in navel orange orchards than potassium deficiency, but newly reclaimed red and yellow soil navel orange orchards often have excessively high acidity and are often prone to calcium deficiency. When calcium is excessive, due to drastic changes in soil reaction and antagonism among various elements, deficiency symptoms of phosphorus, potassium, iron, manganese and boron can be induced.
5. Magnesium
The significance of magnesium in the nutrition of navel orange trees lies first in the main substance of photosynthesis -- it is a main component of chlorophyll, is closely related to photosynthesis, and is related to the formation of other pigments. Its indirect effect on respiration is that it is an activator of many enzymes in physiology and participates in the biosynthesis of various phosphorus-containing compounds.
The magnesium content in navel orange shoots and leaves is higher than in other parts. The adequate value of magnesium is 0.3-0.49% of dry matter in leaves. When it drops below 0.2%, chlorophyll cannot form normally, photosynthesis is hindered, carbohydrate content decreases, and the synthesis of fats and proteins is also affected. Citrus fruit trees absorb relatively more magnesium during fruit development, and seedy varieties are more prone to magnesium deficiency than seedless varieties. Therefore, when seedy varieties are cultivated under magnesium-deficient conditions, alternate bearing is relatively common. Magnesium in the tree is highly mobile; when magnesium is deficient, magnesium from old leaves is transferred to young tissues, and magnesium in leaves is transferred to organs such as fruits. In this way, the first to show symptoms are the mature leaves near the fruit, where irregular yellow streaks appear along the midrib, or the leaf margins fade inward, leaving a green "∧" shape at the leaf base, so magnesium deficiency symptoms often appear on old leaves. The midrib enlarges and becomes suberized, old leaves eventually turn yellow and drop, and small branches weaken and wither; tree vigor declines, flowering and fruiting are few, yield is low, and alternate bearing occurs; fruits are small and pale, the contents of soluble solids and vitamin C both decline, and the fruit does not store well. Magnesium deficiency mostly appears in late summer and early autumn, from the rapid fruit enlargement stage to maturity, and often occurs in acidic soils with a pH of 4.5-5.0. Magnesium deficiency is often accompanied by simultaneous deficiency of iron, manganese and zinc, and soils rich in potassium and calcium must be given additional magnesium.
6. Sulfur
Sulfur is a component of several amino acids, especially cystine, cysteine and methionine. Therefore, sulfur is an indispensable element for protein synthesis. Like nitrogen and phosphorus, it is also a necessary constituent of living matter.
Sulfur exists in the navel orange tree in the sulfhydryl state, and the required amount is less than that of nitrogen, phosphorus, potassium, calcium and magnesium; the optimal amount is 0.2-0.39% of dry matter in leaves. Under field conditions, because sulfur-containing substances are widely applied and irrigation water and air contain sulfur, sulfur deficiency in navel oranges is rarely seen. However, if the soil organic matter content is low, sulfur deficiency may occur. Sulfur deficiency causes chlorosis and blocked protein synthesis, leading to the accumulation of large amounts of free amino acids, weakened tree vigor, clustered shoots, and yellowing and early dropping of new leaves; flowers are numerous but weak, fruits are small and irregular, and in severe cases the juice sacs shrink and dry. When too much sulfate fertilizer is applied to the soil or the concentration of sulfurous acid in the air is high, sulfur excess and poisoning easily result; initially the leaf margins and veins lose their luster and become water-soaked, then dry into a milky white color. When harmed by sulfurous acid gas, necrotic spots appear in the tissues. Applying too much sulfur to the soil also reduces the effectiveness of nitrogen fertilizer.
7. Zinc
Zinc is a component of certain [enzymes] and an activator, and is related to the formation of chlorophyll, auxin, proteins, ribonucleic acid, etc.; it is indispensable in the synthesis of indoleacetic acid.
The suitable zinc content for navel oranges is (25-49) × 10-6; (18-24) × 10-6 is on the low side, and below 18 × 10-6 is felt as deficient. Zinc deficiency in citrus is a disorder commonly occurring worldwide; for example, it is called mottle leaf in California, USA, and green-vein chlorosis in Florida. Navel oranges are more prone to zinc deficiency among citrus varieties. When zinc is deficient, shoot growth is hindered, internodes become markedly shorter, leaves are narrow and small, upright and clustered, and leaf color fades to form a mottled leaf of alternating yellow and green; in severe cases the entire leaf becomes pale yellow or even albino; the canopy becomes upright and dwarf-clustered; flower development is severely affected, with many degenerate flowers, severe bud, flower and fruit drop, and low yield; fruits are small with little juice, and the contents of acid and vitamin C decline. When zinc is excessive, it easily induces iron deficiency, toxic reactions occur in the roots, the tips swell, roots become thick and short, and growth stops.
Zinc deficiency can occur under many soil conditions. The factor affecting zinc availability is mainly soil pH; in soils with a pH greater than 6, available zinc is very scarce (it easily becomes insoluble and unusable); while in acidic sandy soils zinc is easily leached away. Applying too much phosphorus easily affects the plant's absorption of zinc and leads to zinc deficiency. When supplementing zinc, soil application of zinc often cannot solve the problem; foliar spraying is more effective.
8. Boron
Boron can promote the transport of carbohydrates, is closely related to the growth and development of meristematic tissues and reproductive organs, and promotes pollen germination, pollen tube elongation, and fertilization and fruit setting. In addition, boron also helps enhance the resistance of the tree.
The suitable boron content in navel orange trees is a leaf boron content of (30-100) × 10-6. (15-25) × 10-6 is mild to severe deficiency; (3-15) × 10-6 is severe deficiency. When boron is deficient, the internodes of branches and trunk crack and gum oozes, and irregular dead parts appear; young leaves are deformed, with translucent water-soaked small yellow spots, bending backward, and the veins are slightly swollen; in severe cases the main and lateral veins rupture and become suberized, and the leaves curl backward; in the early stage of boron deficiency in young fruit, the rind has milky white raised small spots, and in severe cases sunken black scars appear, or even the whole fruit turns black and gums, and it easily drops; mature fruits are mostly deformed, with a thick and hard rind, a rough surface with wart-like protrusions, little juice and dry flesh, commonly known as "stone fruit," and brown gelatinous material appears in the fruit core and albedo, and soluble solids decrease. When boron is excessive, it causes damage to the tree, or even death.
Boron deficiency is also a nutritional disorder commonly occurring in citrus producing areas, and it has a relatively large impact on tree growth and fruiting. Factors such as low boron content in soil-forming parent rock (granite, gneiss, etc.), leaching of boron in acidic soils (more severe in sandy soil than clay soil), fixation of boron in alkaline soils, and high temperature and drought, heavy rainfall, and excessive lime application all easily lead to boron deficiency in navel orange plants. Boron deficiency is relatively strongly related to variety (strain); in the field, Newhall navel orange shows obvious boron deficiency, while Bonanza is milder. According to research reports: the boron concentrations in the rind and flesh of both Newhall and Bonanza show relatively large increases during the fruit expansion period, indicating that the fruit expansion period is precisely the peak period of boron uptake by the fruit. From the boron dynamics of the fruits of the two varieties, Newhall fruits have a high boron requirement, and the increase is more obvious especially at the peak period. Combined with the leaf boron dynamics, it can be seen that in Newhall, precisely during the peak period of fruit boron uptake during fruit expansion, the boron content of mature old leaves near the fruit attachment site decreases significantly, indicating that the boron in the corresponding old leaves of Newhall is mobile and is lost in large amounts during the expansion period. This is consistent with its leaf boron deficiency symptoms appearing after July during the fruit expansion period. Compared with Newhall, the old leaves of Bonanza do not show an obvious decrease at the peak of fruit boron content, so it is speculated that there are two reasons why Bonanza does not show obvious boron deficiency symptoms: on the one hand, because the boron requirement of Bonanza fruit is relatively small, the change in leaf boron is not obvious at the peak of fruit boron uptake; on the other hand, it may be because the sensitivity of Bonanza leaves to boron is relatively low. Therefore, exogenous boron supplementation measures should be carried out during the fruit expansion period when leaves are boron-deficient. For severely boron-deficient plants, 10-20 grams of boron fertilizer can also be mixed and applied per tree when organic fertilizer is deeply applied to the soil in autumn and winter.
9. Iron
Iron is a necessary element for the synthesis of chloroplast proteins and is essential for the formation of chlorophyll. Ferritin plays an extremely important role in electron transport and redox reactions, and it has an important relationship with the oxidation-reduction, respiration, photosynthesis and nitrogen metabolism of navel orange plants.
The suitable amount of iron required by navel oranges is (50-120) × 10-6; below 35 × 10-6 is felt as deficient. Iron deficiency causes chlorosis; at first the leaves become smaller, then the leaf color fades, the veins remain dark green, and a net-like vein network appears; in severe cases the entire leaf becomes milky yellow, with only the midrib pale green, and it easily drops; shoots that are severely affected bear no fruit at all; fruits become smaller and are mostly yellow-orange to lemon yellow; yield drops substantially, the soluble solids content of the fruit is low, and acid is high; in severe deficiency the whole tree turns yellow, branches wither and leaves drop, few or no fruits are borne, and eventually the whole tree dies. Iron is extremely immobile in the tree; once absorbed by the roots and transported through the xylem into a certain organ, it is fixed, and redistribution is greatly restricted. Thus, unlike deficiency of nitrogen, phosphorus, potassium and other elements, iron deficiency first appears on young leaves.
Iron deficiency in citrus commonly occurs in areas with high soil pH; in China's coastal saline soils and inland calcareous purple soils, because the soil shows an alkaline reaction, the available iron content is on the low side, so iron deficiency chlorosis appears to varying degrees. Excessive application of zinc, manganese and copper has an inhibitory effect on iron absorption; excessive application of phosphorus fertilizer and potassium fertilizer may also cause iron deficiency. Different rootstocks differ somewhat in their ability to absorb iron; trifoliate orange has the poorest iron absorption capacity, while sour orange is stronger, and other rootstocks fall between the two.
10. Manganese
Manganese is necessary for maintaining chloroplast structure and is a component of many enzymes, affecting the synthesis, decomposition and absorption of carbohydrates, etc.
The optimal amount of manganese required by navel oranges is a leaf content of (25-49) × 10-6; below 18 × 10-6 is felt as deficient. When manganese is deficient, chlorophyll synthesis is hindered; leaf size is normal, the veins remain green, and the mesophyll fades to yellow-green or dark green, with pale green spots, finally becoming necrotic. Manganese deficiency symptoms can appear on both old and new leaves, but typical symptoms are more likely to appear on old leaves; the chlorosis symptoms of new leaves are easily confused with iron deficiency and zinc deficiency, but manganese deficiency is not as common as iron deficiency; shaded old leaves are more likely to show symptoms than new leaves. When manganese is excessive, it is toxic to navel oranges; young leaves are yellow and do not turn green, gradually worsening, and the leaf tips turn brown and scorch; scattered black spots appear on old leaves, and basically no new shoots grow.
The available manganese content of soil is mainly affected by pH and redox potential; generally acidic soils have more available manganese, while neutral and alkaline soils are the opposite, so the latter are more prone to manganese deficiency. A decrease in soil redox potential or the addition of reducing agents favors the release of manganese. Practice shows that acidification of orchard soil is an important cause of excessive manganese.
11. Copper
Copper is a component of many oxidase enzymes in the plant and is a constituent of plastocyanin, which participates in energy transfer in photosynthesis in the chloroplast, playing a specific and indispensable role in photosynthesis; copper has a certain relationship with chlorophyll formation, and its presence can increase the concentration of chlorophyll and enhance the stability of chlorophyll and other pigments, preventing the destruction of chlorophyll.
The amount of copper required by navel oranges is very small; the suitable amount is a leaf copper content of (5-12) × 10-6, and generally spraying Bordeaux mixture is already sufficient. When the leaf copper content is below 4 × 10-6, deficiency is felt, and typical copper deficiency symptoms appear at 2 × 10-6 or lower. When copper is deficient, new shoots are long and soft, curling into an "S" shape, the leaf color is dark green, the leaf shape is abnormal, the veins are curved, and pale red, light brownish-red to grayish-black gelatinous material appears on the small twigs at the ends of new shoots, which then wither; the fruit begins to show red-brown gelatinous rust spots around the stem, called "red rust," and some even cover the entire fruit surface; similar to boron deficiency, gum oozes around the fruit core, fruits are small, the rind is hard, and they crack easily, and the fruit-setting rate is low. Copper deficiency is often accompanied by zinc deficiency.
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