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The last decades brought along a tremendous expansion of rubber plantations as well as respective socio-economic transformations. This paper reviews the historical development of rubber cultivation with special reference to intercropping and illustrates the major development steps. The agronomic challenges of intercropping are analyzed and a management classification scheme is suggested. Though the topic of labor always accompanied rubber management, it is nowadays of even higher relevance due to alternative income options, be it due to competing crops such as oil palm, or be it off-farm income opportunities. This development challenges labor intensive permanent intercropping systems. It can thus be concluded that the permanent integration of additional plants needs either to be highly profitable or at least be labor extensive to be adopted on a considerable scale. Given the large area of rubber plantations the latter seems to be more realistic. In this context timber trees might offer promising options if tree selection is properly adapted to site and plantation conditions. Nevertheless, without external interventions, such as land-use planning and implementation, or incentives, the development will be difficult to control.

Aims The aims of this study were (1) to assess which intercropping system is feasible in enhancing soil moisture and promoting crop root growth and (2) to integrate crop root data to assess which intercropping system can reduce interspecific competition and thus increase system productivity. The optimal cropping system was determined by calculating the land equivalent ratio. Methods In this study, we designed two intercropping systems (intercropped apple–soybean and intercropped apple–alfalfa) and three monocropping systems (monocropped apple, monocropped soybean and monocropped alfalfa) that analysed the effects of these intercropping systems on soil moisture, crop roots, interspecific relationships and yields to determine the most suitable cropping system for local promotion. Results Within 50–200 cm from the tree, the apple–soybean intercropping and apple–alfalfa intercropping systems increased soil moisture by 27.91% and 30.23%, respectively, compared to apple monocropping. The root system of intercropped apple was mainly distributed in 20–40 cm soil depth, while the root system of intercropped soybean and intercropped alfalfa moved to shallower soil layers, mainly in 0–20 cm soil depth. In addition, within the distance of 100–200 cm from the tree, soybeans were more competitive than apples and apples were more competitive than alfalfa, whereas apples were more competitive than soybeans and alfalfa at 20–60 cm soil depth. The land equivalent ratio for apple–soybean intercropping system was 1.34 and for the apple–alfalfa intercropping system was 1.18. On balance, apple–soybean intercropping system was more suitable for local promotion. Conclusions These results showed that apple–soybean intercropping system has less interspecific competition than apple–alfalfa intercropping system and that the system is more productive and more suitable for local extension.

Better management of N fertilizer is essential for improving crop productivity. Wheat ( L.)-peanut ( L.) relay intercropping rotation systems are a mainstay of the measures to improve the economic and food security situation in China. Therefore, a 2-year field study (2015-2017) was conducted to evaluate the effect of different N fertilizer management regimes on the photosynthetic characteristics and uptake and translocation of N in peanut in the wheat-peanut rotation system. We used common compound fertilizer (CCF) and controlled-release compound fertilizer (CRF) at the same N-P O -K O proportion (The contents of N, P O , and K O in the two kinds of fertilizer were 20, 15, and 10%, respectively.). The fertilizer was applied on the day before sowing, at the jointing stage or the flag leaf stage of winter wheat, and at the initial flowering stage of peanut in various proportions, with 0 kg N ha as the control. Results showed that split applications of N significantly increased leaf area index (LAI) and chlorophyll content and improved photosynthetic rate, thus increasing the pod yield of peanut. Topdressing N at the jointing stage (S1) or at the flag leaf stage of wheat (S2) and supplying part of the N at the initial flowering stage of peanut increased pod yield. Withholding N until the flag leaf stage (S2) did not negatively affect wheat grain yield; however, it increased N accumulation in each organ and N allocation proportions in the peanut pod, ultimately improving pod yield. With the same N-P O -K O proportion and equivalent amounts of nutrient, CRF can decreased malondialdehyde (MDA) and maintain a relatively high LAI and chlorophyll content at the late growth stage of peanut, prolong the functional period of peanut leaves and delay leaf senescence, resulting in an increase of pod yield over that with CCF. At S1, CRF resulted in a better pod yield than CCF by 9.4%, and at S2 it was 12.6% higher. In summary, applying N fertilizer in three splits and delaying the topdressing fertilization until the flag leaf stage of winter wheat increases total grain yields of wheat and peanut. This method could therefore be an appropriate N management strategy for wheat-peanut relay intercropping rotation systems in China.

Cabbage farming in Sri Lanka relies heavily on synthetic insecticides, but their high costs reduce overall profitability. Additionally, synthetic insecticides pose considerable environmental risks. Therefore, it is important to explore alternative strategies for insect pest management. This study investigated African marigold (Tagetes erecta L.)-based insect pest management strategies for controlling major leaf-eating caterpillar pests in cabbage under field conditions. A Randomized Complete Block Design with three blocks was used to compare five treatments: untreated cabbage sole crop as the control (T1), cabbage treated with synthetic insecticides containing Thiamethoxam 25% (w/w) and Emamectin Benzoate 5% (w/w) (T2), cabbage treated with marigold water extract (50 g fresh plant matter/1 L; T3), cabbage intercropped with marigold as an additive (T4) and cabbage intercropped with marigold in replacement (T5). In T4, marigold was intercropped with cabbage without reducing cabbage density, while in T5, some cabbage plants were replaced by marigold. Treatments T2, T4 and T5 significantly reduced (P<0.05) leaf-eating caterpillar abundance by 94%, 94% and 83%, respectively, compared to the control. Both intercropping methods (T4 and T5) were equally effective in suppressing caterpillar populations, while T3 showed no significant difference (P<0.05) from the control, indicating ineffectiveness of the treatment. Ladybird beetle (Coccinella spp.) abundance significantly increased (P<0.05) under T4 and T5 (by 100 % and 95 %, respectively), but declined sharply under T2 (-95 %), revealing the negative impact of T2 on non-target organisms. Cabbage plant diameter remained consistent across all treatments, confirming that marigold intercropping did not hinder cabbage growth. Economically, additive intercropping (T4) was the most favorable strategy, maintaining full cabbage plant density and eliminating pesticide costs. These results suggest that additive intercropping with African marigold is a promising agronomic strategy for managing leaf-eating caterpillar pests in cabbage production in Sri Lanka.

PurposeIntercropping is an important agricultural management that has been applied worldwide. Although intercropping improves soil nutrients and crop productivity, its effects on the microbial-mediated belowground processes and main drivers remain unclear.MethodsWe performed the same field study at two sites (Site1, Youyu; Site2, Zhangbei) by growing soybean and oat in monoculture and intercropping to investigate their effects on rhizosphere soil properties, enzyme stoichiometry, and soil ecosystem multifunctionality (EMF).ResultsIntercropping increased available phosphorus (Avail-P) by 87% and 16% for oat and soybean compared to the corresponding monoculture in site1, respectively. We also found that intercropping increased the C-acquiring and N-acquiring enzyme activities by 18%-48% in site1. Moreover, intercropping enhanced soil EMF and alleviated microbial P limitations for both oat and soybean compared to the corresponding monoculture in site1. However, all observed parameters were not affected by intercropping in site2, which may be due to the lower Avail-P, mineral nitrogen (Nmin), and precipitation in site2 compared to site1. Moreover, the soil EMF was strongly positively correlated with soil Nmin, Avail-P, air temperature, and precipitation.ConclusionTherefore, intercropping improves soil ecosystem multifunctionality by increasing available nutrients, which are regulated by regional factors.

Intercropping is widely recognized as a sustainable practice for enhancing soil fertility and crop productivity. This study evaluated the effects of different intercropping systems on the physicochemical properties of tobacco-planting soil, nutrient uptake in tobacco plants, yield, and economic benefits to optimize tobacco cultivation. A two-year field experiment (2023–2024) was conducted in Midu and Weishan, Yunnan province, with five treatments: tobacco monoculture (TT), tobacco-buckwheat (TM), tobacco-soybean (TS), tobacco-peanut (TP), and tobacco-sweet potato (TH) intercropping. We measured soil nutrient levels and the nitrogen (N), phosphorus (P), and potassium (K) content in the roots, stems, and leaves of tobacco plants, and comprehensively evaluated leaf yield and sensory quality. The results indicated that the TS treatment significantly increased soil N and P availability and enhanced nitrogen accumulation in plants, elevating leaf N content by 71.43% compared to TT in 2024. The TM treatment improved potassium supply and increased P content in roots and K content in leaves. Economically, TS yielded the highest net return, which was 18.89% greater than TT, with benefit-cost ratios (BCR) of 1.75 (2023) and 1.78 (2024). Conversely, TH had the lowest BCR due to its higher production costs. Sensory evaluation revealed that TS produced tobacco with superior aroma quality and harmony, scoring closely to TT, while TM and TP resulted in a moderate aroma with slightly stronger irritation. In conclusion, the tobacco-soybean (TS) intercropping system demonstrated optimal performance in improving soil nutrient supply, promoting plant nutrient accumulation, and enhancing leaf quality and economic returns, showing high potential for widespread adoption.

Maize’s nitrogen (N) uptake can be improved through maize-legume intercropping. N uptake mechanisms require further study to better understand how legumes affect root growth and to determine maize’s absorptive capacity in maize-legume intercropping. We conducted a two-year field experiment with two N treatments (zero N (N0) and conventional N (N1)) and three planting patterns (monoculture maize ( Zea mays L.) (MM), maize-soybean ( Glycine max L. Merr .) strip intercropping (IMS), and maize-peanut ( Arachis hypogaea L.) strip intercropping (IMP)). We sought to understand maize’s N uptake mechanisms by investigating root growth and distribution, root uptake capacity, antioxidant enzyme activity, and the antioxidant content in different maize-legume strip intercropping systems. Our results showed that on average, the N uptake of maize was significantly greater by 52.5% in IMS and by 62.4% in IMP than that in MM. The average agronomic efficiency (AE) of maize was increased by 110.5 % in IMS and by 163.4 % in IMP, compared to MM. The apparent recovery efficiency (RE) of maize was increased by 22.3% in IMS. The roots of intercropped maize were extended into soybean and peanut stands underneath the space and even between the inter-rows of legume, resulting in significantly increased root surface area density (RSAD) and total root biomass. The root-bleeding sap intensity of maize was significantly increased by 22.7–49.3% in IMS and 37.9–66.7% in IMP, compared with the MM. The nitrate-N content of maize bleeding sap was significantly greater in IMS and IMP than in MM during the 2018 crop season. The glutathione (GSH) content, superoxide dismutase (SOD), and catalase (CAT) activities in the root significantly increased in IMS and IMP compared to MM. Strip intercropping using legumes increases maize’s aboveground N uptake by promoting root growth and spatial distribution, delaying root senescence, and strengthening root uptake capacity.

Aims Intensive soybean/maize intercropping, a specific form of intercropping, holds promise in addressing the challenges posed by increasing food demands, diminishing cropland areas, deteriorating soil quality, and escalating environmental pollution. Methods To evaluate the potential of this system, we conducted a national meta-analysis, quantifying its absolute yield gain (net effect, NE) and land use efficacy (land equivalent ratio, LER). We further investigated the underlying mechanisms by examining local climate, soil properties, and field management practices and then developed random forest (RF) models to assess the system's potential, incorporating current information on natural resources. Results In China, an average NE of 3.2 ± 0.1 Mg ha −1 and LER of 1.4 ± 0.02 were achieved by intensive soybean/maize intercropping. The variance of NE was significantly influenced by air temperature (10%), soybean delay days (8%), and maize plant density (9%). Similarly, the LER was strongly driven by soybean delay days (14%), sunshine hours (11%), and maize density (10%). Notably, this intensive intercropping system efficiently utilizes available resources, such as light, temperature (heat), accumulated temperature, and soil nutrients, particularly in regions characterized by low soil fertility and limited agricultural resources. Ultimately, the RF model estimated substantial overyielding of 2 800 kg per hectare, representing approximately 1.4 times the current soybean and maize production under China's monoculture. Conclusions The implementation of intensive soybean/maize intercropping is highly beneficial throughout China, especially in areas with limited agricultural resources. The Yangtze River Basin, in potentially, emerges as the most suitable region for adopting this intensive intercropping practice.

Surplus use of chemical nitrogen (N) fertilizers to increase agricultural Q9 production causes severe problems to the agricultural ecosystem and environment. This is contrary to N use efficiency and sustainable agricultural production. Hence, this study was designed to investigate the effect of maizesoybean intercropping on N uptake, N yield, N utilization use efficiency, and the associated nitrogen assimilatory enzymes of maize crops under different N fertilization for two consecutive years 2021-2022. The findings of the study showed that intercropping at the optimal N rate (N1) (250 kg N ha-1) increased significantly maize grain yield by 30 and 34%, residue yield by 30 and 37%, and 100-grain weight by 33 and 39% in the year 2021 and 2022, respectively. As compared with mono-cropping, at this optimal N rate, the respective increase (of maize's crop N yield indices) for 2021 and 2022 were 53 and 64% for grain N yield, and 53 and 68% for residue N yield. Moreover, intercropping at N1 resulted in higher grain N content by 28 and 31%, residue N content by 18 and 22%, and total N uptake by 65 and 75% in 2021 and 2022, respectively. The values for the land equivalent ratio for nitrogen yield (LERN) were greater than 1 in intercropping, indicating better utilization of N under the intercropping over mono-cropping. Similarly, intercropping increased the N assimilatory enzymes of maize crops such as nitrate reductase (NR) activity by 19 and 25%, nitrite reductase (NiR) activity by 20 and 23%, and glutamate synthase activity (GOGAT) by 23 and 27% in 2021 and 2022, respectively. Consequently, such increases resulted in improved nitrogen use efficiency indices such as N use efficiency (NUE), partial factor nitrogen use efficiency (PFNUE), nitrogen uptake efficiency (NUpE), and nitrogen agronomic efficiency (NAE) under intercropping than mono-cropping. Thus, this suggests that maize-soybean intercropping under optimal N fertilization can improve the nitrogen status and nitrogen use efficiency of maize crops by regulating the nitrogen assimilatory enzymes, thereby enhancing its growth and yield. Therefore, prioritizing intercropping over an intensive mono-cropping system could be a better option for sustainable agricultural production.

Crop diversification has been put forward as a way to reduce the environmental impact of agriculture without penalizing its productivity. In this context, intercropping, the planned combination of two or more crop species in one field, is a promising practice. On an average, intercropping saves land compared with the component sole crops, but it remains unclear whether intercropping produces a higher yield than the most productive single crop per unit area, i.e., whether intercropping achieves transgressive overyielding. Here, we quantified the performance of intercropping for the production of grain, calories, and protein in a global meta-analysis of several production indices. The results show that intercrops outperform sole crops when the objective is to achieve a diversity of crop products on a given land area. However, when intercropping is evaluated for its ability to produce raw products without concern for diversity, intercrops on average generate a small loss in grain or calorie yield compared with the most productive sole crop (−4%) but achieve similar or higher protein yield, especially with maize/legume combinations grown at moderate N supply. Overall, although intercropping does not achieve transgressive overyielding on average, our results show that intercropping performs well in producing a diverse set of crop products and performs almost similar to the most productive component sole crop to produce raw products, while improving crop resilience, enhancing ecosystem services, and improving nutrient use efficiency. Our study, therefore, confirms the great interest of intercropping for the development of a more sustainable agricultural production, supporting diversified diets.