Agroforestry changes the traditional land use mechanism and has the advantage of intensive eco-economic compound. The photosynthetic characteristics of planting areas are the driving and restricting factors for the accumulation of plant material conversion. To investigate the response of the yield of apple-watermelon intercropping and the yield of fruit trees and crops to photosynthetic characteristics, the growth indexes, photosynthetic characteristics, yield, and benefits of single apple (CK1), single watermelon (CK2) and compound cropping modes were studied respectively. The results showed that the final growth indexes of intercropping apples were higher than those of the single model. However, due to the shading effect of high fruit trees on low crops, the normal growth of watermelon was inhibited, and the growth level of intercropping watermelon was lower than that of single mode. The Pn of apples and watermelons in different planting patterns showed a bimodal trend, and reached the peak value between 10:00–12:00 and 14:00–16:00. The daily variation curve of PAR showed an unimodal trend, and the peak value of apples and watermelons under the two planting patterns appeared between 12:00–14:00 and 10:00–12:00, respectively. Compound planting benefited apples from higher Pn and PAR, and vice versa for watermelon. The diurnal variation of Gs and Tr of intercropping and single species of apple and watermelon first increased and then decreased in an inverted V pattern, the diurnal variation trend of Ci showed a V pattern. The Gs, Tr, and Ci of apple in compound mode were higher than that of watermelon in single mode. The yield of apples increased by 46.34% in the combined apple-watermelon planting mode, and the yield of the combined planting mode was significantly higher than that of the single planting mode due to the advantage of the unit price of apples. In the apple-watermelon compound planting model, the total income was 5.19×105 yuan /hm2, the income of the single apple model was 2.46×105 yuan /hm2, and the income of the single watermelon model was 1.85×105 yuan /hm2. The land utilization rate was 232.20% and the income utilization efficiency was 210.98%.
Research Article
Study on The Response of Yield to Photosynthetic Characteristics under Apple-Watermelon Combined Planting Mode
https://doi.org/10.21203/rs.3.rs-4615642/v1
This work is licensed under a CC BY 4.0 License
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Agroforestry
Apple
Watermelon
Photosynthetic characteristics
yield
As traditional cash crops with large production scale and helping farmers enrich the people, apples, and watermelons have a long history of planting in Ningxia with good fruit quality. The unique regional characteristics have created the climate characteristics of long sunshine and large temperature differences in Ningxia, which is beneficial to the accumulation of sugar and nutrients in fruits. But at the same time, the dryness of Ningxia is above 1.5 in arid and semi-arid regions, and precipitation is the limiting factor of crop growth. Higher light intensity is the driving force for improving fruit yield and quality (Wang et al.2022), but water deficit is a hindrance (Xu et al.2023). Therefore, it is particularly important to improve the diversity of land use and the efficiency of environmental resource use.
As a sustainable land use and management mode, the agroforestry ecosystem is the integration of agriculture and forestry on the same land (He et al.2016). When the relationship between forest and crop species is positive under the agroforestry planting mode, compared with the single mode, the living factors such as water, heat, light, air, and nutrition necessary for the growth of forest and crop can be improved as well as the utilization rate of land (Suhita et al.2023). In its growth stage, it can improve the microclimate of the symbiotic area. Studies have shown that suitable intercropping can generate income and increase production while absorbing and reducing greenhouse gases (Chen et al.2017; Shang et al.2017), while plant litter or residues can be used as green fertilizer to increase organic matter in soil and play a role in soil fertilizer (Liu et al.2023). Grain, vegetables and fruits, forage grass, medicine, and other forest by-products may be obtained under different collocation modes, and resources in limited space will be intensive to pursue higher economic value (Wang et al.2023; Tian et al.2022; Zhang et al.2021; Chen.2021). In the context of global food shortage, environmental damage, resource crisis, and population surge, the agroforestry ecosystem has important practical significance and theoretical value in promoting the virtuous cycle of population, food, resources, and environment given its unique advantages of compound ecological economy (David.2017). The implementation of agroforestry planting is to practice the sustainable development strategy of agriculture and forestry and to open up new ideas and new ways of industrial structure transformation and upgrading.
Many scholars at home and abroad have studied whether intercropping can achieve the unity of the three benefits and the coordinated development of the economy and environment compared with single species from the collocation planting mode of different crops. (Ouyang et al.2023) conducted comparative experiments of maize and potato single species and intercropping, and concluded that the intercropping system could reduce soil nutrient loss and harm degree of soil erosion by reducing excessive evaporation of soil water and making full use of groundwater by crop roots by increasing surface vegetation coverage. (Aiman et al.2023) applied beneficial microorganisms in the single and intercropping processes of barley and alfalfa at the same time, and finally the N and P contents of barley were improved to a greater extent than those of single species. (De Long et al.2023) wheat-broad bean intercropping could reduce disease and increase yield, maximize land use efficiency under the low input level, and form an efficient agricultural production system. (Rebiha et al.2023) significantly improved grain yield, rhizosphere nutrient availability, and utilization efficiency by compound planting wheat and chickpea on low phosphorus soil.
Aiming at the soil and water characteristics in the arid and semi-arid region of central Ningxia, this study surveyed plant photosynthetic physiology under the apple-watermelon compound planting mode in Ningxia Dry farming, water-saving, and high-efficiency agricultural science and Technology Park (Wangtuan Town, Tongxin County, Ningxia). It explored the response relationship between plant photosynthetic physiological characteristics and yield under the apple-watermelon compound planting mode. It also evaluated the economic benefits of the composite planting model(Lu et al.2021). The aim is to provide a theoretical basis for the selection, evaluation, and popularization of fruit and farmer complex models in arid and semi-arid regions of Ningxia. This study has important ecological and economic significance for making full use of land resources and coordinating the conflict between forest and agriculture.
The experimental area is located in Ningxia Dry farming, water-saving and high-efficiency Agricultural Science and Technology Park (36° 50’n, 105° 60’e), Wangtuan Town, Tongxin County, Ningxia. This region belongs to the mid-temperate semi-arid continental climate, with an annual average temperature of 9.2℃, drought and little rain, annual average sunshine of 3026h, annual average precipitation of only 277.5mm, and annual evaporation of more than 2000mm (Yin et al.2021). The mechanical composition of the soil in the test area is as follows: the proportion of sand, silt, and clay is 53.6%, 30.2%, and 16.2%, respectively. According to the classification standard of soil texture, the soil in the test area is sandy loam. The field water holding rate was 24.11%, soil bulk density was 1.32g/cm3, total salt was 0.25g/kg, organic matter, TN, NP, AP, and AK were 8.05g/kg, 0.63g/kg, 0.87g/kg, 23.86mg/kg and 179.28mg/kg, respectively, and soil pH value was 7.79.
1.2 Test materials
In this experiment, two-year-old "Asus" apple seedlings were grafted and planted in April 2020, with row spacing of 1m×3.5m. The watermelon variety "Jincheng No. 5" was planted in April 2022 with a row spacing of 1.6m×0.8m.
1.3 Experimental design
The experiment was conducted from April 2022 to October 2022, and the experimental treatments were divided into apple-watermelon compound planting mode, watermelon single mode (CK1), and apple single mode (CK2). There were 21 apple trees in each plot in the apple-watermelon compound planting mode and apple single seed mode, and 40 watermelon seedlings in each plot in the watermelon single seed mode. Each treatment was repeated 3 times, and the water and fertilizer management was consistent among the three planting patterns.
1.4 Determination index and method
1.4.1 Determination of Plant Growth Index
| Apple | Watermelon | |
|---|---|---|
| Observation index | Tree height, DBH, crown width (north-south, east-west), transverse diameter, and longitudinal diameter of apple fruit | Long vine, thick stem, transverse and longitudinal diameter of watermelon |
| Observation time | 2022.04.15-2022.09.15 | 2022.04.09 -2022.09.20 |
| Observation method | Measuring with tape measure and vernier caliper (accurate to 0.01mm), measuring the transverse diameter and longitudinal diameter of the fruit every 7 days during the fruit expansion period (2022.7.10-2022.8.20), and using the curve of vertical and horizontal diameter growth to indicate the growth law of the fruit. | During the growing phase of watermelon, the vine length and stem thickness were measured with a tape measure and vernier caliper every 7 days until the growth stopped slowly (accurate to 0.01mm). After the watermelon set fruit, the longitudinal and transverse diameter of the watermelon fruit was measured with a tape measure every 7 days, and the growth curve of the vertical and horizontal diameter was used to indicate the law of fruit growth. |
1.4.2 Determination of photosynthetic physiological indexes of plants
The net photosynthetic rate (Pn), photosynthetically active radiation (PAR), transpiration rate (Tr), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) of apples at the flowering stage, physiological fruit setting stage, fruit expansion stage, and maturity stage were measured by portable photosynthesis analyzer system (CI-340) under single and combined planting modes. The seedling stage, elongation stage, fruiting stage (fruit growth period), and maturity stage of watermelon were measured under single and compound planting patterns. The weather conditions for the measurement should be clear and cloud-free for 3 consecutive days, the measurement time is from 8:00 to 20:00, and the measurement is performed once every 2h. During the test, 3 plants with uniform growth were selected from each sample point in the test area, and 3 healthy leaves with similar growth, full extension, and no pests and diseases were selected from each plant. Each index was repeated 3 times. Watermelons and apples under single and compound planting patterns were compared and recorded.
1.4.3 Yield measurement and benefit evaluation of different planting modes
Before ripening and picking, the yield was measured in the sample plot, and the measurement indexes included: fruit yield per plant, maximum and minimum weight of single fruit, maximum and minimum weight of single melon, apple and watermelon yield in apple-watermelon compound planting mode, watermelon single mode and apple single mode.
In the actual production process, how to calculate the area occupied by various crops in the intercropping model, the existing research has not given a unified evaluation standard. At present, the LandEquivalentRatio (LER) (Zhao et al.2023; Lu et al.2021) and income equivalation (IER) are widely used internationally. Its calculation formula is as follows:
In the formula, P1 is the yield per unit area of apple tree in intercropping mode; M1 is the yield per unit of apple tree in monoculture mode. P2 is the yield per unit area of watermelon in intercropping mode. M2 was the yield of watermelon in monoculture mode.
Where:a is the unit price of an apple; b is the unit price of a watermelon.
In this theoretical study, the critical evaluation value of LER and IER is 1.0, if LER and IER > 1.0, it indicates that the intercropping system is more favorable. If LER and IER < 1.0, a single-acting system is more advantageous.
1.5 Data Processing
The test data were collected and sorted out in Excel2016. SPSS22.0 software was used to process data statistics and analysis, in which single-factor Duncan's method was used to analyze the difference significance at the P < 0.05 level, and Pearson correlation analysis was used to evaluate the correlation among all parameters. The graphics in this paper were drawn with Origin2022.
2.1 Research on growth characteristics of plants in different planting modes
2.1.1 Study on growth characteristics of apples under different planting patterns
As can be seen from Fig. 3A, crown width, DBH, and tree height increased by 49.07cm, 16.89mm, and 0.7m, and daily growth was 0.57cm, 0.2mm, and 0.008m, respectively, in apple single mode from flowering to maturity. As can be seen from Fig. 3B, during the whole growth period under the apple-watermelon compound planting mode, the crown width, DBH, and tree height of the apple increased by 62.47cm, 18.46mm, and 0.56m, and the growth rates were 0.73cm/d, 0.21mm/d and 0.007m/d, respectively. The crown width, DBH, and tree height of the compound mode were larger than that of the single mode, and the growth rate of crown width and DBH was higher than that of the single mode, but the growth rate of tree height was slightly lower than that of the single cropping.
As can be seen from Fig. 4, both transverse and longitudinal diameters of apples in the same period of the entire growth period showed that compound planting was larger than single species. The growth rates from physiological drop to ripening were 6.21cm and 6.23cm for the fruits of mono-cropping, which were larger than 6.06cm and 6.01cm for the fruits of compound cropping, and the growth rates were about 0.09cm under different planting modes. The transverse diameter and longitudinal diameter were 9.49cm and 9.26cm, and the transverse diameter and longitudinal diameter of a single apple were 8.43cm and 8.16cm. In combination with the correlation of transverse diameter and longitudinal diameter of apple fruits in different planting modes in Table 2, it can be seen that the correlation of transverse diameter and longitudinal diameter of apples under the combination planting of apple and watermelon is slightly smaller than that of apples of single species, and the growth trend is better, but the fruits of single species are fuller and more uniform.
| Single apple | Apple-watermelon complex planting | |||
|---|---|---|---|---|
| Transverse diameter /cm | Longitudinal diameter /cm | Transverse diameter /cm | Longitudinal diameter /cm | |
| Transverse diameter /mm | 1.000 | 0.996** | 1.000 | 0.988** |
| Longitudinal diameter /mm | 0.996** | 1.000 | 0.988** | 1.000 |
2.1.2 Study on growth characteristics of Watermelon in different planting Modes
Figure 5A shows the distribution range of mean stem diameter and vine length of watermelons under different planting patterns during the whole growth period. Specifically, the average stem diameter of watermelon single species increased by 5.42mm, and the growth rate was 0.067 mm/d. The average stem diameter of watermelon under apple-watermelon combined planting increased by 5.62mm, and the growth rate was 0.07 mm/d. The average length of single species increased by 20.60mm, and the growth rate was 0.258 mm/d. The average watermelon vine length increased by 17.57mm and the growth rate was 0.22mm/d. In the middle of August, the average stem diameter and vine length of watermelon were 10.86mm and 24.88mm respectively under single cropping, and 9.84mm and 21.24mm under compound cropping. According to Table 3, there was a significant correlation between stem diameter and vine length of watermelon under different planting patterns in the growing stage, which were 0.940** and 0.945**, respectively, and the compound had a slight advantage of 0.005 over the single species. It can be seen from Fig. 5B that the distribution range of the mean transverse and longitudinal diameter specifications of watermelon fruit under different planting modes during the whole growth period. The mean transverse and longitudinal diameters of a single watermelon in late May (5.26 mm and 11.24 mm) increased by 20.08 mm and 22.24 mm respectively from the mean transverse and longitudinal diameters measured in mid-August (25.34 mm and 33.48 mm). The initial transverse and longitudinal diameter (4.26 mm and 10.38 mm) of watermelon under compound cultivation increased by 19.22 mm and 19.86 mm from the harvested watermelon (23.48mm and 30.24mm), respectively, and the transverse and longitudinal diameter of watermelon under compound cultivation was smaller than that of single species. In combination with Table 4, it can be seen that the correlation between the horizontal and longitudinal diameter of watermelon fruits under different planting modes from fruit fall to maturity is still significant, which is 0.995** and 0.994**, respectively. In contrast to the correlation between stem length and vine length, the single species has a slight advantage of 0.001 compared with the compound.
| Single watermelon | Apple-watermelon complex planting | |||
|---|---|---|---|---|
| Stem diameter /mm | tendril /mm | Stem diameter /mm | tendril /mm | |
| Stem diameter /mm | 1.000 | 0.940** | 1.000 | 0.945** |
| tendril/mm | 0.940** | 1.000 | 0.945** | 1.000 |
| Single watermelon | Apple-watermelon complex planting | |||
|---|---|---|---|---|
| Transverse diameter /cm | 纵径/cm | Transverse diameter /cm | Longitudinal diameter /cm | |
| Transverse diameter /mm | 1.000 | 0.995** | 1.000 | 0.994** |
| Longitudinal diameter /mm | 0.995** | 1.000 | 0.994** | 1.000 |
The tree height, crown width, and DBH of apples in the combined apple-watermelon planting mode were higher than those in the single cropping mode, and the transverse and longitudinal diameter of apples were the same. The results indicated that the fruit trees could not only grow normally under the compound planting mode, but also improved the growth indexes of the trees because it provided a suitable growing environment, and the multi-planting fruit was fuller and more symmetrical than the single fruit. Therefore, compound planting is conducive to the growth of apple tree bodies and fruit. The stem diameter, vine length transverse diameter, and longitudinal diameter of watermelon were smaller than that of a single species, and the correlation between the two was lower than that of a single species, indicating that the apple-watermelon combined planting mode inhibited the growth of watermelon to some extent.
2.2 Research on photosynthetic characteristics of plants with different planting patterns
2.2.1 Study on daily changes of Pn and PAR of apple and watermelon under different planting patterns
According to Fig. 6A and 6C, there were significant differences in net photosynthetic rate (Pn) and photosynthetically active radiation (PAR) of apples under different planting patterns at different periods, and the daily Pn changes of apples under different planting patterns reached the maximum during 10:00–12:00 and 14:00–16:00, and the overall trend was bimodal. The maximum values of Pn in single planting mode were 11.57umol.m-2.s-1 and 15.41umol.m-2.s-1, and the two peaks of Pn in compound planting mode were 12.50umol.m-2.s-1 and 11.82umol.m-2.s-1. The daily variation trend of PAR in both single and compound planting patterns increased rapidly at first, then decreased rapidly, and then gradually leveled off. The peak values appeared between 12:00 and 14:00, which were 2212.85umol.m-2.s-1 and 2154.33umol.m-2.s-1, respectively.
It can be seen from Fig. 6B and Fig. 6D that the Pn diurnal variation curves of watermelon and apple under single and compound cultivation are still bimodal. The first peak was 23.80umol.m-2.s-1 and 14.26umol.m-2.s-1 from 10:00 to 12:00, and the second peak was 14.21umol.m-2.s-1 and 14.16umol.m-2.s-1 from 14:00–16:00, respectively. The daily variation peak value of watermelon PAR under different planting patterns was between 10:00 and 12:00, and the difference of watermelon PAR between the two planting patterns was the largest during this period. The curve was 2502.41umol.m-2.s-1 in unimodal watermelon mode and 2030.19umol.m-2.s-1 in compound watermelon mode. The curve tends to decline slowly after reaching the first peak and then flatten out. During the whole period from 8:00 to 20:00, the Pn and PAR of the single mode changed more than that of the compound watermelon mode.
2.2.4 Daily changes of Gs, Tr, and Ci of apple under different planting patterns
As can be seen from Table 5, the stomatal conductivity (Gs) and transpiration rate (Tr) of a single species of apple show the same change trend and the value increases first and then decreases in an unimodal pattern. The larger the value of Tr, the larger the value of Gs, and the peak value from 12:00 to 14:00 is 118.3mmol.m− 2.s− 1 and 1.2mmol. The diurnal variation of intercellular carbon dioxide concentration (Ci) showed the opposite trend, with a trough value of 568.6umol/mol from 12:00 to 14:00. The Gs and Tr curves of apples in the combined apple-watermelon planting mode were still unimodal, and the maximum values were 147.4mmmol.m− 2.s− 1 and 1.5mmmol.m− 2.s− 1 in the period from 14:00–16:00. Ci is the minimum value of 385.4umol/mol during the diurnal variation from 14:00 to 16:00.
| 8:00–10:00 | 10:00–12:00 | 12:00–14:00 | 14:00–16:00 | 16:00–18:00 | 18:00–20:00 | ||
|---|---|---|---|---|---|---|---|
| Single apple | Gs(mmol/m2/s) | 95.37 | 99.07 | 118.30 | 113.11 | 100.44 | 96.56 |
| Tr(mmol/m2/s) | 0.53 | 0.83 | 1.21 | 1.09 | 0.71 | 0.63 | |
| Ci(umol/mol) | 610.15 | 545.37 | 568.59 | 585.19 | 613.22 | 622.15 | |
| Apple-watermelon complex planting | Gs(mmol/m2/s) | 107.37 | 107.52 | 117.22 | 147.37 | 109.30 | 106.15 |
| Tr(mmol/m2/s) | 0.61 | 0.93 | 1.10 | 1.51 | 0.84 | 0.41 | |
| Ci(umol/mol) | 550.26 | 445.00 | 405.00 | 385.37 | 555.26 | 645.11 |
2.2.5 Diurnal variation of Gs, Tr, and Ci of watermelon in different planting modes
As can be seen from Table 6, Gs and Tr of watermelon of a single species showed the same daily variation trend, increasing to 224.7mmol.m− 2.s− 1 and 2.0mmol.m− 2.s− 1 from 14:00–16:00 in the early stage, and then decreasing continuously. The daily variation of Ci first decreased and reached the bottom between 14:00–16:00, with a minimum value of 257.0umol/mol, and then continued to rise. The daily variation trends of Gs, Tr, and Ci of watermelon in apple-watermelon compound planting mode were consistent with those of watermelon in single planting mode, and the peak values of Gs, Tr, and Ci were 162.8mmol.m− 2.s− 1 and 1.7mmol.m− 2.s− 1 between 14:00–16:00. The Ci valley value was 362.0umol/mol during the period from 14:00–16:00.
| 8:00–10:00 | 10:00–12:00 | 12:00–14:00 | 14:00–16:00 | 16:00–18:00 | 18:00–20:00 | ||
|---|---|---|---|---|---|---|---|
| Single watermelon | Gs(mmol/m2/s) | 95.26 | 104.59 | 213.44 | 224.67 | 178.44 | 100.44 |
| Tr(mmol/m2/s) | 0.44 | 1.13 | 1.88 | 2.07 | 1.46 | 0.74 | |
| Ci(umol/mol) | 563.00 | 550.28 | 325.30 | 256.93 | 337.33 | 575.00 | |
| Apple-watermelon complex planting | Gs(mmol/m2/s) | 83.48 | 102.26 | 158.04 | 162.85 | 102.26 | 100.26 |
| Tr(mmol/m2/s) | 0.22 | 0.56 | 1.41 | 1.71 | 1.16 | 0.85 | |
| Ci(umol/mol) | 536.19 | 425.48 | 387.52 | 362.04 | 462.52 | 587.44 |
The diurnal variation curves of Gs, Tr, and Ci of both apple and watermelon were unimodal, the diurnal variation trends of Gs and Tr were first increasing and then decreasing, and the diurnal variation trends of Ci were opposite. The difference is that for apples, Gs, Tr, and Ci of single species of apple were smaller than those of apple-watermelon combined planting mode at different periods in one day. However, the Gs, Tr, and Ci of watermelon in single cultivation mode were higher than those in compound cultivation mode at all periods in one day. In addition, the relationship among the photosynthetic characteristics of Gs, Tr, and Ci day is that the more stomata on the leaves, the greater the degree of opening, the more water transpiration per unit leaf area, and the less and lower CO2 used for photosynthesis between cells. There is a proportional relationship between Gs and Tr and an inverse relationship between them and Ci.
2.3 Effects of photosynthetic characteristics of plants in different planting modes on yield
As can be seen from Fig. 7, the respective yields (TPA) of fruit trees and crops under single apple (CK1), combined apple (IA), single watermelon (CK2) and combined watermelon (IM) modes, The degree of correlation between diurnal variation of photosynthetic characteristics (PG1-6, PAR1-6, Gs1-6, Tr1-6, Ci1-6) and the same period of one day (8:00–20:00). The yield of apples under the combination of apple-watermelon is higher than that of single apple, and the single watermelon can get more light than that under the combination planting. The increase in microclimate temperature and higher levels of Pn and PAR ensure the conversion and absorption of nutrients and the accumulation of organic matter in watermelon, which lays the foundation for the high yield of watermelon. In CK1, Ci, Pn, and PAR had the strongest influence on apple yield, and in CK2, Tr, Gs, Pn, and PAR had the greatest influence on watermelon yield. The main influencing factors of intercropping apple and watermelon yield were Gs, Ci, Tr, Pn, PAR, and Tr, Pn, PAR, respectively.
2.3.1 Plant yield of different planting modes
As can be seen from Fig. 8, the maximum, minimum, and average single fruit weight of apples under apple-watermelon composite planting were 0.32kg, 0.18kg, and 0.25kg, respectively, which were all larger than the 0.35kg, 0.2kg, and 0.28kg of apples under single mode. The average fruit yield per plant of 30 apples under composite planting was higher than that of 23 apples per plant under single planting. The opposite results were obtained for the watermelon under the combined planting mode. The maximum, minimum, and average fruit weight of watermelon were 13kg, 5kg, and 0.25kg, respectively, which were larger than the 15kg, 6kg, and 10.5kg of watermelon under the single planting mode, but the average fruit weight of watermelon per plant under different planting modes was the same as 1.
2.3.2 Economic effects of plant yields corresponding to different planting patterns
As can be seen from Table 7, the yield of apples increased by 46.34% and the yield of watermelons decreased by 14.14% in the combined planting mode compared with the single planting mode, which further verified the promoting effect of the combined planting on apple and inhibiting effect on watermelon. The total yield of a single apple and single watermelon was 1.01×105 (kg.hm− 2), which was slightly lower than that of apple and watermelon combined with apple and watermelon, which was 1.02×105kg.hm-2. Based on the average market price of apple and watermelon in that year, the total output value of a single apple and single watermelon was 4.31×105 yuan.hm− 2, and the total output value of apple-watermelon composite planting was 5.19×105 yuan.hm− 2. The land equivalent ratio LER is 2.32 > 1 and LUR is 232.2%. Because it is greater than the critical evaluation value 1, it indicates that it is meaningful to carry out agroforestry planting and improve the utilization rate of land. It was also found that the yield equivalent ratio IER of 2.11 was also greater than 1, and the economic benefit produced by the apple-watermelon composite planting model was greater than that of the single model. The combined planting model could maximize the crop yield on the limited land area, effectively increase the yield per unit area of land, and the economic benefit increased by 46.34% compared with the single model.
| Single apple | Single watermelon | Apple-watermelon complex planting | Land equivalent ratio | Land utilization rate | Yield equivalent ratio | ||
|---|---|---|---|---|---|---|---|
| Apple | Watermelon | LER | LUR(%) | IER | |||
| Plant yield(kg.hm− 2) | 2.46×104 | 7.71×104 | 3.60×104 | 6.62×104 | 2.32 | 232.20 | — |
| Plant income(元.hm− 2) | 2.46×105 | 1.85×105 | 3.60×105 | 1.59×105 | — | — | 2.11 |
Due to the influence of shading of apple-watermelon compound planting, watermelon did not get enough light under the single mode, which inhibited the normal growth of watermelon, and the yield and value of watermelon decreased compared with that of single species. However, due to the improvement of the microclimate of apple growth, the income of fruit trees and crops under agroforestry cultivation is still greater than that under single mode.
Different planting patterns will have a certain impact on plant growth characteristics, and the existing research (Zhou et al.2023) has the opposite results. Apple and sweet potato intercropping competed for soil nutrients in barren sandy land, so apple tree crown width, DBH, tree height, stem diameter, and fruit diameter of sweet potato were better under mono-cropping mode than under composite planting. In the agroforestry system, the canopy of high crops will have a certain shading effect on the light distribution of low crops, which will greatly limit the growth and development of low crops. During the intercropping between fruit trees and peanuts (Huang et al.2023), different fruit trees have different shading effects on the growth indexes of peanuts. Because fruit trees have obvious advantages in spatial height, they make more full use of light than peanuts to shade peanuts. Such results are also consistent with this study. As the region of this study is located in an arid and semi-arid region, the competition of light between the studied crops, apple, and watermelon, is greater than the competition of nutrients. In the agroforestry system, shade is the main factor limiting crop growth (Wang et al.2020), and insufficient light intensity and light time limit the accumulation of photosynthetic products.
Different planting patterns will have a certain impact on plant photosynthetic characteristics. Solar radiation is the energy source for crop photosynthesis and yield formation, and the unreasonable distribution of light resources in the agro-fruit intercropping complex system will affect the accumulation of organic matter in intercropping crops and is also an important environmental factor affecting cotton yield (Wang et al.2020; Kong et al.2008). In the jujube cotton intercropping model (Yang et al.2019), the photosynthetic characteristics of cotton decreased significantly at the flowering and bolling stage compared with that of single cropping. In this study, it was found that the Pn and PAR of watermelon in the compound cropping mode were weaker than those in the single cropping mode, so the growth characteristics of watermelon in the single cropping mode were better than those in the compound cropping mode, which was caused by the shading of fruit trees on crops. The Pn and PAR of compound mode apples were stronger than those of single cropping, so the growth characteristics of intercropping apples were better than those of single cropping apples. It was found that the bimodal curve of Pn in the compound cropping mode and the mono-cropping mode reached its peak value at 10:00–12:00 and 14:00–16:00 respectively. The peak value was due to the increase of plant Pn with time, and the plant reached the light saturation state at 10:00–12:00 when the plant Pn reached its peak value. After that, due to the reason of plant lunch break, Pn gradually decreased, and the reason for the peak value between 14:00 and 16:00 was that plants began to carry out photosynthesis after the lunch break. The daily variation of PAR is an unimodal curve that peaks between 10:00 and 12:00, which is consistent with the results of many previous studies (Yun et al.2011; Tian et al.2013).
Different planting patterns have a certain impact on yield and benefit. A representative study of corn-soybean belt planting in composite planting (Raza et al.2021) shows that appropriate crop allocation can yield more in a limited area. Compared with a single species, corn can not reduce production but also harvest soybean output, which not only solves the contradiction of cropland contention (Chen et al.2018) but also promotes the adjustment of the industrial structure by increasing production and income to achieve rural revitalization. On the other hand, certain shading effects are beneficial to the ginger-grape three-dimensional intercropping model (Peng et al.2023) Intercropping can not only meet the normal growth needs of ginger plants but also reduce the burn rate of plants, to ensure the final survival rate and increase the yield. Some studies have also shown that intercropping combined management of crops under economic forests can effectively improve economic returns. Chinese medicinal herbs Bai and Bai were planted under thin shell pecan (Qin et al.2023), especially the degree of oxide stress of intercropping Bai, and the photosynthetic capacity of habitat under the crown edge of walnut was lower than that of single species. In this study, it was found that the fruit and tree growth of apples under the combined cropping mode was better than that under the single cropping mode. The Pn, PAR, Gs, and Tr of the apple under the combined cropping mode were larger than those under the single cropping mode, and the Ci was smaller than that under the single cropping mode. The growth characteristics of apples in the compound cropping mode were better than those in the single cropping mode, and the growth of apples was more uniform. The Pn, PAR, Gs, and Tr of watermelon intercropping with apple were smaller than that of single cropping mode, and Ci was larger than that of single cropping mode. Therefore, the combined planting mode had an inhibitory effect on the growth of watermelon and thus affected the yield of watermelon, but the total yield of combined planting was better than that of single cropping mode.
The photosynthetic physiological characteristics of Pn, PAR, Gs, Tr, and Ci in different planting modes were higher than that of a single apple in different periods in one day. The daily changes of Pn, PAR, Gs, and Tr gradually increased with the decrease of Ci in an inverse relationship, while the daily changes of Pn, PAR, Gs, and Tr were in a positive relationship. The combined planting mode increased the yield of apples by 46.34% and decreased the yield of watermelons by 14.14%. The land utilization rate of composite planting mode is 232.20%, and composite planting can maximize the crop yield on the limited land area and effectively increase the yield per unit area of land. Compound planting pattern plays an important role in improving land use. The economic benefit of the compound planting mode increased by 46.34% compared with that of the single mode, and the benefit utilization efficiency was 210.98%. The economic benefit of the compound planting mode was greater than that of the single mode. By playing the role of the law of material and energy circulation transformation in the ecosystem, the effect of intensive management is achieved, which accords with the economic effect principle of obtaining maximum output with minimum input.
Author Contribution
Z.P.P. and L.Q. mainly performed data processing and wrote the main manuscript text. Z.P.P., L.Q., L.S.T. and E-S.S worked together on the diagram. D.X.M. and M.X.H. collected the data needed for the research in the research area, W.C.F. and Z.Z.X. And Z.W. further refined and revised the text manuscript and diagrams, and all the authors reviewed the manuscript.
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No competing interests reported.