Soybean maize strip intercropping:A solution for maintaining food security in China

The practice of intercropping leguminous and gramineous crops is used for promoting sustainable agriculture,optimizing resource utilization,enhancing biodiversity,and reducing reliance on petroleum products.However,promoting conventional intercropping strategies in modern agriculture can prove challenging.The innovative technology of soybean maize strip intercropping(SMSI)has been proposed as a solution.This system has produced remarkable results in improving domestic soybean and maize production for both food security and sustainable agriculture.In this article,we provide an overview of SMSI and explain how it differs from traditional intercropping.We also discuss the core principles that foster higher yields and the prospects for its future development.

Assessment of Nitrogen Fixation, Uptake, and Leaching in Maize/Soybean Intercropping System at Varied Soil Depths and under Phosphorus Application in Chinese Agricultural Settings

The study of Nitrogen fixation, uptake, and leaching at different soil depths in the co-cultivation of maize and soybean under phosphorus fertilization is important for sustainable agriculture. This study was conducted in Quzhou, Hebei Province, China, with MC812 maize and Jidou12 soybean varieties. Soil samples were taken from each plot to create a composite sample. The results show that nitrogen concentration varies at different depths and is higher in all treatments between 40 and 100 cm. Incorporating intercropping of maize and soybeans into farming practices can lead to more sustainable and environmentally friendly agriculture in China.

Assessing the Influence of Phosphorus Fertilization on the Growth and Yield of Maize/Soybean Intercrop by Analyzing Nitrogen Uptake

Intercropping, particularly the combination of maize and soybeans, has been widely recognized for its potential to improve nitrogen uptake and promote sustainable agriculture. This study examines the patterns of nitrogen uptake in maize and soybean intercropping systems under different growth stages and phosphorus fertilization levels and investigates the influence of nitrogen uptake on growth parameters such as plant height, leaf area, and biomass accumulation in the maize/soybean intercrop under different phosphorus fertilization regimes. The study also collected chlorophyll samples at different growth stages of maize in monoculture and intercropping with maize or soybean. The results showed that plant height was greater in V10 in both fertilized and unfertilized treatments for intercropped maize and soybean, and chlorophyll concentration was higher in VT intercropped maize. The results also showed a higher accumulation of biomass. Understanding the growth dynamics of these plants in monoculture and intercropping systems and the impact of fertilization practices is crucial for optimizing crop productivity and sustainability in agricultural systems.

Assessing the Efficacy of Wheat-Soybean Based Intercropping System at Different Plant Densities in Bambili, Cameroon

Wheat is one of the most important cereals in the world, serving as a staple for millions globally. In the wake of the geopolitical crisis between Russia and Ukraine, it has become incumbent for many countries to invest in wheat production. Improving cropping systems for wheat production is paramount. Intercropping cereals with legumes has tremendous advantages. Therefore, this study was designed to optimize wheat production by intercropping it with soybean at different densities. Between March and August 2023, a randomized complete block design trial was conducted in Bambili, North West of Cameroon with treatments T1 (wheat monocrop at 200,000 plants ha−1), T2 (soybean monocrop at 250,000 plants ha−1), T3 (200,000 wheat and 125,000 soybean ha−1), T4 (100,000 wheat and 250,000 soybean ha−1), T5 (200,000 wheat and 250,000 soybean ha−1) and T6 (100,000 wheat and 125,000 soybean ha−1). Results revealed that growth parameters of wheat were not significantly influenced by monocrop or intercrop. The yield of wheat was significantly higher in the monocrop than the intercrop treatments, with slight variation amongst the intercrop treatments. Soybean yield was higher in the monocrop than in the intercrop, with no variations amongst the intercrop treatments. Only the land equivalence ratio (LER) for T5 was greater than 1.0. The competitive ratio for T5 was 0.54 for wheat and 1.90 for soybean, comparatively lower than the other monocrop treatments. Intercropping wheat and soybean at 200,000:250,000 ratio is recommended.

Effects of Spatial Row Arrangement and Time of Planting Intercrops on Performance of Groundnut (Arachis hypogaea L.) under Maize (Zea mays L.)—Groundnut Intercropping System in Ejura

In monoculture, crop failure due to biotic or abiotic causes can result in partial or total output failure. The yield, socio-economic, and environmental effects of intercropping on the farmer and the environment as a whole have not received much attention. There is a dearth of knowledge on the productivity of maize-groundnut intercrops in Ghana regarding the relative timing of planting and spatial arrangement of component crops. Therefore, the objective of the study was to determine the effects of spatial row arrangement and the time of planting intercrops on the productivity of groundnut under maize-groundnut intercropping. The 5 × 3 factorial field experiment was undertaken at the Miminaso community in the Ejura-Sekyedumase municipality of the Ashanti Region of Ghana during the 2020 cropping seasons. Treatments were evaluated in a Randomized Complete Block Design (RCBD) with three replicates. The levels of row arrangement of intercrops were: one row of maize and one row of groundnut (1M1G), one row of maize and two rows of groundnut (1M2G), two rows of maize and one row of groundnut (2M1G), two rows of maize and two rows of groundnut (2M2G), sole maize and sole groundnut (M/G). The levels of time of introducing groundnut included simultaneous planting of intercrops (0 WAP), planting groundnut one week after planting maize (1 WAP) and planting groundnut two weeks after planting maize (2 WAP). There were significant (P 0.05) treatment interactions for pod and seed yields of groundnut throughout the study. The highest groundnut pod yields of 1815.00 kg/ha and 2359.00 kg/ha were recorded by the 0WAP × 1M2G treatment in the major and minor seasons of 2020, respectively, while the highest groundnut seed yields of 741.00 kg/ha and 726.00 kg/ha were recorded in the major and minor rainy seasons of 2020 by 1WAP × G and 0WAP × G treatments, respectively. The highest seed yields of groundnut (404 kg/ha and 637 kg/ha for major and minor rainy seasons, respectively) were produced by 1WAP × 2M2G.

Identifying the critical phosphorus balance for optimizing phosphorus input and regulating soil phosphorus effectiveness in a typical winter wheat-summer maize rotation system in North China

Phosphorus(P)is a nonrenewable resource and a critical element for plant growth that plays an important role in improving crop yield.Excessive P fertilizer application is widespread in agricultural production,which not only wastes phosphate resources but also causes P accumulation and groundwater pollution.Here,we hypothesized that the apparent P balance of a crop system could be used as an indicator for identifying the critical P input in order to obtain a high yield with high phosphorus use efficiency(PUE).A 12-year field experiment with P fertilization rates of 0,45,90,135,180,and 225 kg P_(2)O_(5)ha^(-1)was conducted to determine the crop yield,PUE,and soil Olsen-P value response to P balance,and to optimize the P input.Annual yield stagnation occurred when the P fertilizer application exceeded a certain level,and high yield and PUE levels were achieved with annual P fertilizer application rates of 90-135 kg P_(2)O_(5)ha^(-1).A critical P balance range of 2.15-4.45 kg P ha^(-1)was recommended to achieve optimum yield with minimal environmental risk.The critical P input range estimated from the P balance was 95.7-101 kg P_(2)O_(5)ha^(-1),which improved relative yield(>90%)and PUE(90.0-94.9%).In addition,the P input-output balance helps in assessing future changes in Olsen-P values,which increased by 4.07 mg kg^(-1)of P for every 100 kg of P surplus.Overall,the P balance can be used as a critical indicator for P management in agriculture,providing a robust reference for limiting P excess and developing a more productive,efficient and environmentally friendly P fertilizer management strategy.

Performance of Maize (Zea mays L.) and Land Equivalent Ratio under Maize-Groundnut (Arachis hypogea L.) Intercropping System

Soil fertility continues to decline in Ghana due to unsustainable human activities like bush burning, quarrying, improper farming practices, among others. To resolve this challenge, crop farmers resort to continuous use of mineral fertilizers in Ghana, which contaminates the environment and makes crop farming less sustainable and productive. One of the strategies to improve soil fertility and productivity for sustainable crop yields is intercropping. Studies were, therefore, undertaken at Miminaso in the Ejura-Sekyedumase municipality of Ashanti Region of Ghana during the 2020 cropping seasons to determine the effects of spatial row arrangement and time of planting maize and groundnut intercrops on productivity of maize and land equivalent ratio (LER). One row of maize and one row of groundnut (1M1G), one row of maize and two rows of groundnut (1M2G), two rows of maize and one row of groundnut (2M1G), two rows of maize and two rows of groundnut (2M2G), sole maize (M) and sole groundnut (G) were factorially arranged with concurrent planting of intercrops (0 WAP), planting groundnut one week after planting maize (1 WAP) and planting groundnut two weeks after planting maize (2 WAP) in a Randomized Complete Block Design with three replicates. There were significant treatment interaction (P < 0.05) effects for shelling percentage for maize in both seasons of the trial. In the major season of 2020, the highest shelling percentage of 79.30% was associated with 0 WAP × M, while in the minor season of 2020, the highest shelling percentage of 75.02% was recorded by 0 WAP × 2M1G. The treatment interaction effects for maize grain yield were significant only in the minor season of 2020 with the highest maize grain yield of 6341 kg/ha being produced by the sole maize treatment, followed by 1 WAP × 2M2G (6152 kg/ha). The highest LER of 3.05 was associated with 1 WAP × 2M2G in the minor season of 2020. Planting groundnuts within the first week of planting maize (1 WAP) increased maize seed yield and LER in two rows of maize and two rows of groundnut (2M2G) row arrangements.

Effect of Limited Single Irrigation on Yield of Winter Wheat and Spring Maize Relay Intercropping

A field experiment was conducted during the 2002/2003 cropping season of winter wheat （Triticum aestivum） and spring maize （Zea mays） to evaluate the effect of limited single drip irrigation on the yield and water use of both crops under relay intercropping in a semi-arid area of northwestern China. A controlled 35 mm single irrigation, either early or late, was applied to each crop at a certain growth stage. Soil water, leaf area, final grain yield and yield components such as the thousand-grain weight, length of spike, fertile spikelet number, number of grains per spike, and grain weight per spike were measured, and water use efficiency and leaf area index were calculated for the irrigated and non-irrigated relay intercropping treatments and sole cropping controls. The results showed that yield, yield components, water use efficiency, and leaf area index in the relay intercropping treatments were affected by limited single drip irrigation during various growth stages of wheat and maize. The total yields in the relay intercropping treatment irrigated during the heading stage of wheat and the heading and anthesis stage of maize were the highest among all the treatments, followed by that irrigated during the anthesis stage of wheat and silking stage of maize; so was the water use efficiency. Significant differences occurred in most yield components between the irrigated and non-irrigated relay-intercropping treatments. The dynamics of the leaf area index in the relay-intercropped or solely cropped wheat and maize showed a type of single-peak pattern, whereas that of the relay intercropping treatments showed a type of double-peak pattern. Appropriately, limited single irrigation and controlled soil water content level could result in higher total yield, water use efficiency, and leaf area index, and improved yield components in relay intercropping. This practice saved the amount of water used for irrigation and also increased the yield. Therefore, heading stage of wheat and heading and anthesis stage of maize were suggested to be the optimum limited single irrigation time for relay-intercropped wheat and maize in the semi-arid area.

Transfer characteristics of nitrogen fixed by leguminous green manure crops when intercropped with maize in northwestern China

To ascertain the possibility of cultivating maize using biological nitrogen fixation(BNF)by leguminous green manure crops in maize/leguminous green manure intercropping systems,BNF and nitrogen(N)transfer were studied in Xining and Wuwei,two typical northwestern Chinese cities.The experimental treatments included monocultured maize,monocultured green manures(hairy vetch and common vetch),and their intercropping systems.The proportions of N derived from the atmosphere(%N_(dfa))in intercropping systems were not significantly different from that in monocultured green manure systems at either experimental site,except for that in hairy vetch(HV)in Xining.The amount of N derived from the atmosphere(N_(dfa))of common vetch(CV)significantly decreased from 1.16 and 1.10 g/pot in monoculture to 0.77 and 0.55 g/pot when intercropped with maize,in Xining and Wuwei,respectively,and the N_(dfa) of HV when intercropped significantly decreased from 1.02 to 0.48 g/pot in Xining.In the intercropping systems in Xining and Wuwei,the amounts of N transferred(N_(transfer))from CV to maize were 21.54 and 26.81 mg/pot,accounting for 32.9 and 5.9%respectively of the N accumulation in maize,and the values of N_(transfer) from HV to maize were 39.61 and 46.22 mg/pot,accounting for 37.0 and 23.3%,respectively,of the N accumulation in maize.Path analysis showed that soil nutrient and green manure biomass were mainly related to N_(dfa),and thatδ^(15) N had a primary relationship with N_(transfer).We found that 5.9-37.0%of N accumulation in maize was transferred from green manures,and that the N transfer ability to maize of HV was higher than that of CV.In conclusion,intercropping with leguminous green manures provided a feasible way for maize to effectively utilize biologicallyfixed N.

Research and Breeding Application Progress of the Technique of Producing Double Haploid of Wheat by Wide Hybridization between Wheat and Maize

The technique of producing doublehaploid of wheat by distant hybridization between wheat and maize has characterized with better inducing effect, shorter in- ducing period, easy operation, and so on. At present, it is the most efficient and has great potential of application in breeding of wheat. This article reviewed princi- ple and production process of the technique, research situation of the three key in- dicators of the technology（embryo rate, seedling rate and success rate of doubling）in recent years, and application of the technology in breeding, genetics, germplasm improvement of wheat. At last, both the achievements and the direction of further improvement and development of the technology in our program were discussed.

Highly-efficient Intercropping Mode and Selection of Suitable Peanut Varieties in Maize and Peanut Intercropping Systems

[Objective] The aim was to explore efficient maize and peanut intercrop-ping mode and select suitable peanut varieties of the mode in Yungui Plateau. [Method] In the test, 6 cropping methods were set by randomized block design. Yields and economic benefits were measured in mature stage with Excelland DPS. [Result] Compared with monoculture, maize and peanut intercropping systems took advantages and LER values were proved higher than 1. In the intercropping system with maize and Yun peanut No.3 at 2∶2, in particular, the value of LER was 1.40 and compound yield reached 9 036 kg/hm2; the net output values of maize kernel and fresh/dry peanut pod increased by 182.63% and 140.59%, compared with maize by monoculture. In addition, the output values of Yun peanut No.3 by monoculture and intercropping system increased by 5 069 and 3 272 yuan/hm2, respectively, than Yanshan conventional peanut varieties. [Conclusion] The efficient intercropping system with maize and peanut mode at 2∶2 mode in Yungui plateau and the Yun peanut No.3 exhibited higher yield and economic benefit advantages, compared with Yanshan conventional planting peanut varieties.

Inheritance and Sequence Homology Analysis of the Maize DNA Introgressed into the Wheat Doubled Haploid Plant Through Wheat×Maize Cross

A maize (Zea mays L.) genome_specific repeated DNA sequence (clone MR64) has been transferred into one DH line of wheat through wheat (Triticum persicum Vav. ex Zhuk.) and maize cross. In the present study by RFLP analysis the authors proved that this DNA sequence could stably transmit into DH3 plants, the next generation derived from DH2 self_crossing. A similarity search in all DNA databases using BLASTN program showed that the DNA sequence of MR64 had as high as 93% identity to PREM_2 and 79% to Opie_2 in nucleotides. Both PREM_2 and Opie_2 are known as retrotransposons in maize genome, suggesting that MR64 likely is the partial sequence of a maize retrotransposon. Therefore, the results indicate that some retrotransposon might involve the DNA introgression from maize to wheat genome through wide fertilization. Stable inheritance of this maize genome_specific retrotransposon_like DNA in the wheat genome opens up the possibility of using retrotransposon as a new tool for gene tagging, function analysis, and insertional mutagenesis in wheat genome.

Genetic Analysis of Embryo Production Frequency in Wheat × Maize Cross

A DH population derived from C49S-87/01Y1-1069 was used to study the inheritance of wheat haploid embryo production frequency（EPF） in wheat × maize cross with the mixed major gene and polygene inheritance model of quantitative traits. The results showed that the EPF of wheat × maize cross was controlled by two dominant epistatic genes and polygene with gene effects of 1.95 for the first major gene, 6.69 for the second one and 2.80 for the polygene. The inheritability of major genes was as high as 72.09%, suggesting that the differences in EPF among wheat materials were mainly influenced by genotype. However, non-genetic factors were still important, especially for wheat materials with low EPF.

Effects of Intercropping Patterns on Dry Matter Accumulation and Transportation of Maize(Zea mays L.) and Soybean[Glycine max(L.) Merrill]

[Objective] The aim was to discuss the group dry matter accumulation and economic benefits under the patterns of intercropping maize （Zea mays L.） with soy-bean [Glycine max （L.） Merril ]. [Methods] Zhengdan-958 and Luhuang-1 were used as the testing breeds to study the effects of intercropping patterns on dry matter accumulation and transportation of maize and soybean in Huang-huai-hai. [Results] For maize, the dry matter accumulation amounts per hectare of intercropping was significant higher than that of the monoculture patterns, especial y after silking, when it reached extremely level; while for soybean, the dry matter accumulation amounts before flowering and after flowering of monocropping were al significantly higher than that of the intercropping patterns. For both maize and soybean, the transfer amounts of monocropping were al significantly or extremely significantly higher than that of intercropping; and the transfer ratio of maize intercropping was 0.59% higher than that of maize monocropping, while for soybean, it was 4.74% higher. Fitted dry matter accumulation with Logistic equation, it showed that the difference in maximum dry matter accumulation rate between maize monocropping and intercropping reached significant level, while for soybean, the maximum dry matter accumulation rate and its appearance time as wel as duration time between intercropping and monocropping were al reached significant level. The total land equivalent ratio of intercropping was 1.30. From yield and output value, the total yield of intercropping were 10.97 t/hm2, 0.64% and 326.85% higher than monocropping of maize and soy-bean, respectively. The total output value of intercropping was 25 796.23 yuan/hm2, respectively 12.67% and 104.68% higher than of maize and soybean monocropping. [Conclusion] The study lays a basis for improving grain yield and economic benefits.

Maize-soybean strip intercropping： Achieved a balance between high productivity and sustainability

Intercropping is one of the most vital practice to improve land utilization rate in China that has limited arable land resource. However, the traditional intercropping systems have many disadvantages including illogical field lay-out of crops, low economic value, and labor deficiency, which cannot balance the crop production and agricultural sustainability. In view of this, we developed a novel soybean strip intercropping model using maize as the partner, the regular maize-soybean strip intercropping mainly popularized in northern China and maize-soybean relay-strip intercropping principally extended in southwestern China. Compared to the traditional maize-soybean intercropping systems, the main innovation of field lay-out style in our present intercropping systems is that the distance of two adjacent maize rows are shrunk as a narrow strip, and a strip called wide strip between two adjacent narrow strips is expanded reserving for the growth of two or three rows of soybean plants. The distance between outer rows of maize and soybean strips are expanded enough for light use efficiency improvement and tractors working in the soybean strips. Importantly, optimal cultivar screening and increase of plant density achieved a high yield of both the two crops in the intercropping systems and increased land equivalent ratio as high as 2.2. Annually alternative rotation of the adjacent maize-and soybean-strips increased the grain yield of next seasonal maize, improved the absorption of nitrogen, phosphorus, and potasium of maize, while prevented the continuous cropping obstacles. Extra soybean production was obtained without affecting maize yield in our strip intercropping systems, which balanced the high crop production and agricultural sustainability.

Nitrate Leaching from Maize Intercropping Systems with N Fertilizer Over-Dose

A 2-yr field experiment was conducted on a calcareous alluvial soil with four summer maize intercropping systems at Shangzhuang Experiment Station （116.3°E, 39.9°N） in the North China Plain. The objective was to determine nitrate leaching from intercropping systems involving maize （Zea mays L.）： sole maize （CK）, maize ＋ soybean （CST）, maize ＋ groundnut （CGT）, maize ＋ ryegrass （CHM）, and maize ＋ alfalfa （CMX）. Intercropping greatly reduced nitrate accumulation in the 100-200 cm soil layers compared with maize monoculture. Nitrate accumulation under intercropping systems decreased significantly at the 140-200 cm soil depth; the accumulation varied in the order CK〉CST〉CMX〉CHM〉CGT. However, compared to the CK treatment, nitrate leaching losses during the maize growing period were reduced by 20.9- 174.8 （CGT）, 35.2-130.8 （CHM）, 60.4-122.0 （CMX）, and 30.6-82.4 kg ha-1 （CST）. The results also suggested that intereropping is an effective way to reduce nitrogen leaching in fields with N fertilizer over-dose.

Biochemical and microbial properties of rhizospheres under maize/ peanut intercropping

Maize/peanut intercropping system shows the significant yield advantage. Soil microbes play major roles in soil nutrient cycling and were affected by intercropping plants. This experiment was carried out to evaluate the changing of rhizosphere microbial community composition, and the relationship between microbial community and soil enzymatic activities, soil nutrients in maize/peanut intercropping system under the following three treatments： maize （Zea mays L.） and peanut （Arachis hypogaea L.） were intercropped without any separation （NS）, by half separation （HS） using a nylon net （50 μm） and complete separation （CS） by using a plastic sheet, respectively. The soil microbial communities were assessed by phospholipid fatty acid （PLFA）. We found that soil available nutrients （available nitrogen （Avail N） and available phosphorus （Avail P）） and enzymatic activities （soil urase and phosphomonoesterase） in both crops were improved in NS and HS treatments as compared to CS. Both bacterial and fungal biomasses in both crops were increased in NS followed by HS. Furthermore, Gram-positive bacteria （G＋） in maize soils were significant higher in NS and HS than CS, while the Gram-negative （G-） was significant higher in peanut soil. The ratio of normal saturated to monounsaturated PLFAs was significantly higher in rhizosphere of peanut under CS treatment than in any other treatments, which is an indicator of nutrient stress. Redundancy analysis and cluster analysis of PLFA showed rhizospheric microbial community of NS and HS of both plants tended to be consistent. The urase and Avail N were higher in NS and HS of both plants and positively correlated with bacteria, fungi （F） and total PLFAs, while negatively correlated with G＋/G- and NS/MS. The findings suggest that belowground interactions in maize/peanut intercropping system play important roles in changing the soil microbial composition and the dominant microbial species, which was closely related with the improving of soil available nutrients （N and P） and enzymatic activities.

Allelopathy of decomposed maize straw products on three soilborn diseases of wheat and the analysis by GC-MS

In northern China, the soil-born diseases of wheat have been getting more and more serious under a new farming system that returns maize straw to the field. In order to investigate the allelopathy of the decomposed maize straw products on three soil-born diseases of wheat, culture dish and pot experiments were conducted and the compounds in the products were identified by gas chromatography-mass spectrometry （GC-MS）. Culture dish experiments showed that the mycelial growth, sclerotia formation amount and total weight of Rhizoctonia cerealis were promoted at concentrations of 0.03, 0.06 and 0.12 g mL-1 and inhibited at concentration of 0.48 g mL-1 of the decomposed products. No significant effects were found of the product concentrations on average weight of the sclerotia. Mycelial growth of Gaeumannomyces graminis was promoted at almost all concentrations except the highest one. Mycelial growth and spore germination of Bipolaris sorokiniana were significantly inhibited by all concentrations of the decomposed products, with enhanced inhibition effects along with the increased concentrations. The length, number and dry weight of roots together with the root superoxide dismutase activity were promoted by the lowest concentration （0.03 g mL-1）, with a synthetic effect index of 0.012, and inhibited by other concentrations. The ion leakage of roots was increased and the root peroxidase activity of roots was lowered by all the treatments. Pot experiments revealed that occurrence of the sharp eyespot was reduced by 0.03 and 0.06 g mL-1 of decomposed products after irrigation. However, the incidence rates and disease indexes were significantly increased by 0.12, 0.24 and 0.48 g mL-1 of decomposed products. The results indicated that incidence rates and disease indexes of the take-all were significantly promoted after being irrigated with the decomposed products, while occurrences of the common rot didn＇t change, significantly. GC-MS results showed that the compounds of the decomposed products included organic acids, esters, hydrocarbons, amides and aldehydes, with the proportions 25.26, 24.01, 17.22, 14.39 and 7.73%, respectively. Further analysis investigated that the allelochemicals identified in straw decomposed products contained p-hydroxybenzoic acid （9.21%）, dibutyl phthalate （6.94%）, 3-phenyl-2-acrylic （5.06%）, 4-hydroxy-3,5-dimethoxybenzoic acid （2.26%）, hexanoic acid （1.73%）, 8-octadecenoic acid （1.06%）, 3-（4-hydroxy-3-methoxy-phenyl）-2-propenoic acid （1.04%）, 4-hydroxy-3-methoxy-benzoic acid （0.94%） and salicylic acid （0.94%）.

Effect of intercropping on maize grain yield and yield components

Smallholders in developing countries commonly use intercropping to produce crops with higher yield and value. Many intercropping studies have been conducted under experimental conditions, but few studies have been performed in farmers’ fields. We conducted a 4-year study using data from real farms to examine the relationships between yield and yield components of intercropped maize in the North China Plain. Three field experiments were conducted to compare the suitability of different maize varieties in intercropping. In the farm study, the grain yield of maize intercropped with watermelon was reduced by more than one third as compared to maize in wheat-maize double cropping, mainly due to lower ear density and lower 100-grain weight. Under real farm conditions, the yield of intercropped maize increased with increasing ear density and 100-grain weight, while yield of sole maize increased with increasing grain number per ear and 100-grain weight. In the field experiments, the maize cultivars commonly used in double cropping gave similar yields when grown in the intercropping system and their yields were closely related to ear density and 100-grain weight. Our results demonstrated that ear density, rather cultivar, was a key factor affecting the productivity of intercropped maize. Therefore,maintaining high ear density is a practical way for promoting productivity of maize in farmers’ intercropping practices.

Trends of Yield and Soil Fertility in a Long-Term Wheat-Maize System

The sustainability of the wheat-maize rotation is important to China＇s food security. Intensive cropping without recycling crop residues or other organic inputs results in the loss of soil organic matter （SOM） and nutrients, and is assumed to be non- sustainable. We evaluated the effects of nine different treatments on yields, nitrogen use efficiency, P and K balances, and soil fertility in a wheat-maize rotation system （1991-2010） on silt clay loam in Shaanxi, China. The treatments involved the application of recommended dose of nitrogen （N）, nitrogen and phosphorus （NP）, nitrogen and potassium （NK）, phosphorus and potassium （PK）, combined NPK, wheat or maize straw （S） with NPK （SNPK）, or dairy manure （M） with NPK （M1NPK and M2NPK）, along with an un-treated control treatment （CK）. The mean yields of wheat and maize ranged from 992 and 2 235 kg ha-1 under CK to 5 962 and 6 894 kg ha-1 under M2NPK treatment, respectively. Treatments in which either N or P was omitted （N, NK and PK） gave significantly lower crop yields than those in which both were applied. The crop yields obtained under NP, NPK and SNPK treatments were statistically identical, as were those obtained under SNPK and MNPK. However, M2NPK gave a significant higher wheat yield than NP, and MNPK gave significant higher maize yield than both NP and NPK. Wheat yields increased significantly （by 86 to 155 kg ha-1 yr-1） in treatments where NP was applied, but maize yields did not. In general, the nitrogen use efficiency of wheat was the highest under the NP and NPK treatments; for maize, it was the highest under MNPK treatment. The P balance was highly positive under MNPK treatment, increasing by 136 to 213 kg ha-1 annually. While the K balance was negative in most treatments, ranging from 31 to 217 kg ha^-1 yr^-1, levels of soil available K remained unchanged or increased over the 20 yr. SOM levels increased significantly in all treatments. Overall, the results indicated that combinations of organic manure and inorganic nitrogen, or retuming straw with NP is likely to improve soil fertility, increasing the yields achievable with wheat-maize system in a way which is environmentally and agronomically beneficial on the tested soil.