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Cereal and legume intercropping has been widely adopted to increase crop productivity in sustainable farming systems worldwide. Among different intercropping combinations, millet and peanut intercropping can be adapted to most water-limited areas. However, there are few studies on the differences in yield characteristics and nitrogen use efficiency between millet/peanut intercropping and monocultures under different nitrogen (N) application rates. The objective of this study was to determine the yield advantages and economic benefits, as well as the appropriate N application rate, of millet/peanut intercropping. A two-year field experiment was conducted with three cropping patterns (monoculture millet, monoculture peanut and millet/peanut intercropping) and four N rates (0, 75, 150 and 225 kg ha−1). The results showed that the land equivalent ratio (LER) and net effect (NE) of the intercropping system reached their highest levels at the N input of 150 kg ha−1 in 2018 and 2019 (1.04 for LER, 0.347 Mg ha−1 for NE, averaged across two years). Millet was the dominant crop in the intercropping system (aggressivity of millet and peanut (Amp)>0, competitive ratio of millet and peanut (CRmp)>1), and millet yields achieved their highest values at N inputs of 225 kg ha−1 for monoculture and 150 kg ha−1 for intercropping. NUE reached its highest levels with N inputs of 150 kg ha−1 for all planting patterns over the two years. Intercropping combined with an N input of 150 kg ha−1 achieved the highest net income of 2 791 USD ha−1, with a benefit-cost ratio of 1.56, averaged over the two years. From the perspective of economics and agricultural sustainable development, millet/peanut intercropping at 150 kg N ha−1 seems to be a promising alternative to millet or peanut monoculture.

To clarify the response and adaptability of peanut under salt stress, Huayu 25 was used as the material, and non-salt stress (CK), 0.15% salt stress (S1), and 0.3% salt stress (S2) were applied as three treatments. The study analysed the effects of salt stress on photosynthetic characteristics, photosynthetic substances accumulation and distribution as well as the ecological adaptability of peanuts. The results showed that net photosynthetic rate (Pn), SPAD value, leaf area, and peanut yield were reduced under salt stress. Pn in CK was 13.71 and 28.72% higher than that in S1 and S2 at the 50th day after planting, respectively. At the same growth period, the SPAD value among treatments was ranked as follows: CK>S1>S2. The 100-pod mass, 100-kernel mass, kernel rate to pod, and pod mass per plant were reduced under salt stress, and the trend was CK>S1>S2. The distribution proportion of dry matter in different organs of peanut plant was changed to adapt to such stress. Roots under salt stress intensively distributed in a 0–40 cm soil layer for salt resistance. Dry mass proportion in stems and pods increased during the vegetative stage and early period of reproductive stage, respectively. The maximum growth rates of the pod volume, pod dry weight, and seed kernel dry weight all declined, and the pod and kernel volume at harvest were reduced, improving the seed plumpness under salt stress. This finding could be useful in growing peanut in saline soil.

Potassium (K) deficiency significantly decreases photosynthesis due to leaf chlorosis induced by accumulation of reactive oxygen species (ROS). But, the physiological mechanism for adjusting antioxidative defense system to protect leaf function in maize (Zea mays L.) is unknown. In the present study, four maize inbred lines (K-tolerant, 90-21-3 and 099; K-sensitive, D937 and 835) were used to analyze leaf photosynthesis, anatomical structure, chloroplast ultrastructure, ROS, and antioxidant activities. The results showed that the chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), photochemical quenching (qP), and electron transport rate of PSII (ETR) in 90-21-3 and 099 were higher than those in D937 and 835 under K deficiency treatment. Parameters of leaf anatomical structure in D937 that were significantly changed under K deficiency treatment include smaller thickness of leaf, lower epidermis cells, and vascular bundle area, whereas the vascular bundle area, xylem vessel number, and area in 90-21-3 were significantly larger or higher. D937 also had seriously damaged chloroplasts and PSII reaction centers along with increased superoxide anion (O2−) and hydrogen peroxide (H2O2). Activities of antioxidants, like superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), were significantly stimulated in 90-21-3 resulting in lower levels of O2− and H2O2. These results indicated that the K-tolerant maize promoted antioxidant enzyme activities to maintain ROS homeostasis and suffered less oxidative damage on the photosynthetic apparatus, thereby maintaining regular photosynthesis under K deficiency stress.

Potassium (K) deficiency is one of the major abiotic stresses which has drastically influenced maize growth and yield around the world. However, the physiological mechanism of K deficiency tolerance is not yet fully understood. To identify the differences of root morphology, physiology and endogenous hormones at different growing stages, two maize inbred lines 90-21-3 (tolerance to K deficiency) and D937 (sensitive to K deficiency) were cultivated in the long-term K fertilizer experimental pool under high potassium (+K) and low potassium (−K) treatments. The results indicated that the root length, volume and surface area of 90-21-3 were significantly higher than those of D937 under −K treatment at different growing stages. It was noteworthy that the lateral roots of 90-21-3 were dramatically higher than those of D937 at tasselling and flowering stage under −K treatment. Meanwhile, the values of superoxide dismutase (SOD) and oxidizing force of 90-21-3 were apparently higher than those of D937, whereas malondialdehyde (MDA) content of D937 was obviously increased. Compared with +K treatment, the indole-3-acetic acid (IAA) content of 90-21-3 was largely increased under −K treatment, whereas it was sharply decreased in D937. On the contrary, abscisic acid (ABA) content of 90-21-3 was slightly increased, but that of D937 was significantly increased. The zeatin riboside (ZR) content of 90-21-3 was significantly decreased, while that of D937 was relatively increased. These results indicated that the endogenous hormones were stimulated in 90-21-3 to adjust lateral root development and to maintain the physiology function thereby alleviating K deficiency.

Potassium is an important nutrient element requiring high concentration for photosynthetic metabolism. The potassium deficiency in soil could inhibit soybean (Glycine max (L.) Merr.) photosynthesis and result in yield reduction. Research on the photosynthetic variations of the different tolerant soyben varieties should provide important information for high yield tolerant soybean breeding program. Two representative soybean varieties Tiefeng 40 (tolerance to K+ deficiency) and GD8521 (sensitive to K+ deficiency) were hydroponically grown to measure the photosynthesis, chlorophyll fluorescence parameters and Rubisco activity under different potassium conditions. With the K-deficiency stress time extending, the net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) of GD8521 were significantly decreased under K-deficiency condition, whereas the intercellular CO2 concentration (Ci) was significantly increased. As a contrast, the variations of Tiefeng 40 were almost little under K-deficiency condition, which indicated tolerance to K+ deficiency variety could maintain higher efficient photosynthesis. On the 25th d after treatment, the minimal fluorescence (F0) of GD8521 was significantly increased and the maximal fluorescence (Fm), the maximum quantum efficiency of PSII photochemistry (Fv/Fm), actual photochemical efficiency of PSII (ϕPSII), photochemical quenching (qP), and electron transport rate of PSII (ETR) were significantly decreased under K+ deficiency condition. In addition, the Rubisco content of GD8521 was significantly decreased in leaves. It is particularly noteworthy that the chlorophyll fluorescence parameters and Rubisco content of Tiefeng 40 were unaffected under K+ deficiency condition. On the other hand, the non-photochemical quenching (qN) of Tiefeng 40 was significantly increased. The dry matter weight of Tiefeng 40 was little affected under K+ deficiency condition. Results indicated that Tiefeng 40 could avoid or relieve the destruction of PSII caused by exceeded absorbed solar energy under K-deficiency condition and maintain natural photosynthesis and plant growth. It was an essential physiological mechanism for low-K-tolerant soybean under K-deficiency stress.