Detailed Explanation of the Key Technical Points of Jujube-Grain Intercropping
1 Scientific Basis of Jujube-Grain Intercropping
1.1 Seize the time difference between the growth of jujube trees and intercrops to make full use of fertilizer and water resources. The jujube tree is a fruit tree that sprouts late, sheds its leaves early, and has a relatively short annual growth period. It generally begins to sprout in mid-April and sheds its leaves in mid-to-late October, @#@245@#@ is sown in late September and harvested in early June of the following year. The symbiotic period of jujube trees and wheat is about 80 to 90 days. From mid-May to early June is the period when wheat flowers, fills grain, and matures, mainly absorbing phosphorus and potassium fertilizer, with nitrogen fertilizer as a supplement. And the jujube tree is precisely in the period of growing leaves, differentiating young buds, and growing new jujube heads, mainly absorbing nitrogen fertilizer, with phosphorus and potassium fertilizer as a supplement. Therefore, when jujube trees are intercropped with wheat, the conflict over fertilizer and water is not great. In early June, jujube trees enter the flowering and fruit-setting stage, and their fertilizer demand is at a peak, while wheat begins to be harvested. And crops such as foxtail millet and summer corn that have just been sown are still in the seedling emergence stage, with relatively small fertilizer demand, generally not affecting the flowering and fruit setting of jujube trees. After jujube trees are harvested in mid-to-late September, in order to store nutrients, the demand of jujube leaves for phosphorus and potassium fertilizer rises, but wheat is still in the seedling emergence stage, with relatively small absorption of phosphorus and potassium fertilizer, and sufficient base fertilizer was applied before wheat sowing, so the conflict over fertilizer between jujube trees and wheat is not great.
1.2 Use the difference in distribution of jujube tree roots and intercrop roots in the soil to make full use of fertilizer and water resources. The distribution of jujube tree roots is mainly horizontal, concentrated in the 30 to 70 cm soil layer within the tree canopy, accounting for 65% to 75% of the total root system. The root distribution outside the canopy is sparse and low in density, while the roots of intercrops are concentrated in the 0 to 20 cm cultivated layer. Jujube trees mainly absorb fertilizer and water from deep soil layers below 30 cm, and mainly within the canopy. Intercrops mainly absorb fertilizer and water from the cultivated layer within 20 cm, mainly outside the canopy. Therefore, jujube-grain intercropping can improve the utilization rate of fertilizer and water more than open fields.
1.3 The jujube tree canopy is relatively low, with sparse branches, small leaves, little shading, and relatively high light transmittance, basically not affecting the requirements of intercrops for light intensity and light reception. ① Jujube-wheat intercropping. From greening to jointing, wheat requires a certain light intensity and light reception, and at this time jujube trees have just sprouted not long ago, basically not affecting the light of wheat. From early May to early June, wheat enters the heading, flowering, and grain-filling maturation stage, and its required light intensity and light reception are only 25% to 30% of full light. At this time, the branches and leaves of jujube trees enter a rapid growth period. After jujube leaves unfold, the average area of a single leaf is 7.4 to 9.8 sq cm, and as they sway with the wind they cannot form a fixed shadow area, basically meeting wheat's light requirements at each growth and development stage. ② Jujube intercropped with foxtail millet or legumes. Foxtail millet and legumes are shade-tolerant crops with relatively low light saturation points, so intercropping can meet the crops' light requirements. ③ Jujube intercropped with summer corn. After wheat harvest, summer corn can be rotated in. Summer corn has a relatively high light saturation point and is a thermophilic crop. However, its light compensation point is relatively low, and it has the characteristics of short light duration and high light efficiency. Moreover, summer corn is a C4 plant, and under weaker light conditions it can still accumulate a certain amount of dry matter, so intercropping jujube trees with summer corn can also meet the light requirements and obtain relatively high yields.
2 Modes of Jujube-Grain Intercropping
2.1 Intercropping mode with jujube as the main crop and grain as the supplementary crop. This mode is suitable for areas with more land and fewer people. That is, the plant spacing and row spacing of jujube trees are 4 m x 6 m, with 37 jujube trees planted per mu, occupying an area of 432 sq m, and grain crops occupying an area of 235 sq m. Or adopt a double-row belt-type intercropping mode, that is, large and small row spacing of 4 m, small row spacing of 4 m, and large row spacing of 10 m, with 24 jujube trees planted per mu, occupying an area of 384 sq m, and grain crops occupying an area of 283 sq m.
2.2 Intercropping mode with grain as the main crop and jujube as the supplementary crop. This mode is suitable for areas with more people and less land. The row spacing of jujube trees is relatively large, generally 15 m is appropriate, with a plant spacing of 4 m, 11 jujube trees planted per mu, occupying an area of 176 sq m, and grain crops occupying an area of 491 sq m. Or adopt a double-row belt-type intercropping mode with a plant spacing of 4 m, small row spacing of 4 m, and large row spacing of 18 m. Plant 15 jujube trees per mu, occupying an area of 240 sq m, and grain crops occupying an area of 427 sq m.
2.3 Intercropping mode giving consideration to both jujube and grain. This mode is suitable for areas with balanced population and land. The plant spacing of jujube trees is 4 m, the row spacing is 8 m, 21 jujube trees are planted per mu, occupying an area of 336 sq m, and grain crops occupy an area of 331 sq m. Or adopt a double-row belt-type intercropping mode with a plant spacing of 4 m, small row spacing of 4 m, and large row spacing of 12 m, planting 21 jujube trees per mu.
3 Key Technical Points of Jujube-Grain Intercropping
The key technology of jujube-grain intercropping is to properly regulate the conflicts between jujube trees and intercrops over fertilizer, water, and light, so as to achieve mutual benefit and mutual advantage between jujube and grain crops and realize high yields of both jujube and grain.
3.1 Grasp appropriate planting density. Row spacing has an obvious impact on air temperature, humidity, light, and wind speed, and is also an important factor affecting jujube and grain yields. Therefore, according to the cultivation purpose, measures should be adapted to local conditions and overall arrangements should be made. For jujube as the main crop, a row spacing of 6 m is better; for grain as the main crop, a row spacing of 15 m is better; for giving consideration to both jujube and grain, a row spacing of 8 m is better.
3.2 Choose a suitable planting row direction. Row direction has a certain impact on jujube yield. Practice has proved that planting jujube trees in a north-south row direction gives more uniform light exposure under the canopy, and the daily light reception is also greater than that of an east-west row direction. Therefore, it is generally better to plant jujube trees in a north-south row direction, while also adapting to local conditions and applying this flexibly.
3.3 Properly control jujube tree height. Tree height has a certain relationship with the amount of direct light received. In order to improve light energy utilization and economic benefits, tree height should be controlled below 6 m, so the trunk-setting height should preferably be 1 to 1.5 m.
3.4 Prune reasonably and control tree shape. According to investigations, canopy shape has varying degrees of impact on the growth and yield of jujube trees and intercrops. A dense canopy with crowded branches has poor ventilation and light transmission, causes the fruiting position to move outward, lowers the fruit-setting rate, and aggravates the impact on intercrops. Therefore, the canopy shape should preferably be an open-center shape with scattered branches.
3.5 Selection and arrangement of intercrops. Selecting suitable intercrops for reasonable arrangement is one of the key techniques for regulating the "three conflicts" between jujube trees and intercrops. The selected intercrops should have the characteristics of a phenological period staggered from that of jujube trees, short plants, strong shade tolerance, a short growth period, and an early maturity period. According to practical experience, the following crops are relatively suitable for intercropping
Wheat crops include winter wheat, spring wheat, barley, etc. These grain crops have small plants and shallow root distribution, and their phenological periods are staggered with those of jujube trees, making them ideal crops for jujube-grain intercropping.
Legumes include soybean, pea, mung bean, adzuki bean, etc. These crops have short plants, strong shade tolerance, a short growth period, and early maturity. They also have their own nitrogen fixation effect, making them relatively good crops for intercropping with jujube trees.
Miscellaneous grain crops include corn, foxtail millet, sesame, peanut, and cotton, etc., all of which can be intercropped with jujube trees. But reasonable layout and arrangement must be done well, because these crops are all light-loving crops, yet their light saturation points and compensation points differ greatly. When intercropping with jujube trees, on the side close to the jujube trees, first sow several rows of legume crops, and then sow foxtail millet, corn, sesame, cotton, etc. Adopt a "short-tall-short or short-medium-tall-medium-short type" arrangement combination, which is beneficial for ventilation and light transmission, meets the intercrops' requirements for light intensity and light reception, helps alleviate the conflicts between jujube trees and intercrops over fertilizer and water, and also helps prevent and control diseases and insect pests and facilitates management under the trees.