Excessive rainfall provides a favorable condition for field mold infection of plants, which triggers field mold (FM) stress.  If FM stress occurs during the late maturation stage of soybean seed, it negatively affects seed yield and quality.  To investigate the responses of soybean seed against FM stress and identify the underlying biochemical pathways involved, a greenhouse was equipped with an artificial rain producing system to allow the induction of mold growth on soybean seed.  The induced quality changes and stress responses were revealed on the levels of both transcriptome and metabolome.  The results showed that soybean seeds produced under FM stress conditions had an abnormal and inferior appearance, and also contained less storage reserves, such as protein and polysaccharide.  Transcriptional analysis demonstrated that genes involved in amino acid metabolism, glycolysis, tricarboxylic acid, β-oxidation of fatty acids, and isoflavone biosynthesis were induced by FM stress.  These results were supported by a multiple metabolic analysis which exhibited increases in the concentrations of a variety of amino acids, sugars, organic acids, and isoflavones, as well as reductions of several fatty acids.  Reprogramming of these metabolic pathways mobilized and consumed stored protein, sugar and fatty acid reserves in the soybean seed in order to meet the energy and substrate demand on the defense system, but led to deterioration of seed quality.  In general, FM stress induced catabolism of storage reserves and diminished the quality of soybean seed in the field.  This study provides a more profound insight into seed deterioration caused by FM stress.

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.

In China, the abuse of chemical nitrogen (N) fertilizer results in decreasing N use efficiency (NUE), wasting resources and causing serious environmental problems.  Cereal-legume intercropping is widely used to enhance crop yield and improve resource use efficiency, especially in Southwest China.  To optimize N utilization and increase grain yield, we conducted a two-year field experiment with single-factor randomized block designs of a maize-soybean intercropping system (IMS).  Three N rates, NN (no nitrogen application), LN (lower N application: 270 kg N ha^–1), and CN (conventional N application: 330 kg N ha^–1), and three topdressing distances of LN (LND), e.g., 15 cm (LND1), 30 cm (LND2) and 45 cm (LND3) from maize rows were evaluated.  At the beginning seed stage (R5), the leghemoglobin content and nitrogenase activity of LND3 were 1.86 mg plant^–1 and 0.14 mL h^–1 plant^–1, and those of LND1 and LND2 were increased by 31.4 and 24.5%, 6.4 and 32.9% compared with LND3, respectively.  The ureide content and N accumulation of soybean organs in LND1 and LND2 were higher than those of LND3.  The N uptake, NUE and N agronomy efficiency (NAE) of IMS under CN were 308.3 kg ha^–1, 28.5%, and 5.7 kg grain kg^–1 N, respectively; however, those of LN were significantly increased by 12.4, 72.5, and 51.6% compared with CN, respectively.  The total yield in LND1 and LND2 was increased by 12.3 and 8.3% compared with CN, respectively.  Those results suggested that LN with distances of 15–30 cm from the topdressing strip to the maize row was optimal in maize-soybean intercropping.  Lower N input with an optimized fertilization location for IMS increased N fixation and N use efficiency without decreasing grain yield.

Soybean is one of the major oil seed crops, which is usually intercropped with other crops to increase soybean production area and yield.  However, soybean is highly sensitive to shading.  It is unclear if soybean morphology responds to shading (i.e., shade tolerance or avoidance) and which features may be suitable as screening materials in relay strip intercropping.  Therefore, in this study, various agronomic characteristics of different soybean genotypes were analyzed under relay intercropping conditions.  The soybean materials used in this study exhibited genetic diversity, and the coefficient of variations of the agronomic parameters ranged from 13.84 to 72.08% during the shade period and from 6.44 to 52.49% during the maturity period.  The ratios of shading to full irradiance in stem mass fraction (SMF) were almost greater than 1, whereas opposite results were found in the leaves.  Compared with full irradiance, the average stem length (SL), leaf area ratio (LAR) and specific leaf area (SLA) for the two years (2013 and 2014) increased by 0.78, 0.47 and 0.65 under shady conditions, respectively.  However, the stem diameter (SD), total biomass (TB), leaf area (LA), number of nodes (NN) on the main stem, and number of branches (BN) all decreased.  During the shady period, the SL and SMF exhibited a significant negative correlation with yield, and the SD exhibited a significant positive correlation with yield.  The correlation between the soybean yield and agronomic parameters during the mature period, except for SL, the first pod height (FPH), 100-seed weight (100-SW), and reproductive growth period (RGP), were significant (P<0.01), especially for seed weight per branch (SWB), pods per plant (PP), BN, and vegetative growth period (VGP).  These results provide an insight into screening the shade tolerance of soybean varieties and can be useful in targeted breeding programs of relay intercropped soybeans.