Magnesium deficiency is a frequently occurring limiting factor for crop production due to low levels of exchangeable Mg (ex-Mg) in acidic soil, which negatively affects sustainability of agriculture development. How Mg fertilization affects crop yield and subsequent physiological outcomes in different crop species, as well as agronomic efficiencies of Mg fertilizers, under varying soil conditions remain particular interesting questions to be addressed. A meta-analysis was performed with 570 paired observations retrieved from 99 field research articles to compare effects of Mg fertilization on crop production and corresponding agronomic efficiencies in different production systems under varying soil conditions. The mean value of yield increase and agronomic efficiency derived from Mg application was 8.5% and 34.4 kg kg -1 respectively, when combining all yield measurements together, regardless of the crop type, soil condition, and other factors. Under severe Mg deficiency (ex-Mg < 60 mg kg -1 ), yield increased up to 9.4%, nearly two folds of yield gain (4.9%) in the soil containing more than 120 mg kg -1 ex-Mg. The effects of Mg fertilization on yield was 11.3% when soil pH was lower than 6.5. The agronomic efficiency of Mg fertilizers was negatively correlated with application levels of Mg, with 38.3 kg kg -1 at lower MgO levels (0-50 kg ha -1 ) and 32.6 kg kg -1 at higher MgO levels (50-100 kg ha -1 ). Clear interactions existed between soil ex-Mg, pH, and types and amount of Mg fertilizers in terms of crop yield increase. With Mg supplementation, Mg accumulation in the leaf tissues increased by 34.3% on average; and concentrations of sugar in edible organs were 5.5% higher compared to non-Mg supplemented treatments. Our analysis corroborated that Mg fertilization enhances crop performance by improving yield or resulting in favorable physiological outcomes, providing great potentials for integrated Mg management for higher crop yield and quality.

Seed priming is a presowing technique in which seeds are moderately hydrated to the point where pregermination metabolic processes begin without actual germination. Seeds are then redried to near their actual weight for normal handling. Seeds can be soaked in tap water (hydropriming), aerated low-water potential solutions of polyethylene glycol or salt solutions (KNO3, KH2PO4, KCl, NaCl, CaCl2 or MgSO4; osmopriming), plant growth regulators, polyamines (hormonal priming), plant growth-promoting bacteria (biopriming), macro or micronutrients (nutripriming) or some plant-based natural extracts. Here, we review: (1) seed priming as a simple and effective approach for improving stand establishment, economic yields and tolerance to biotic and abiotic stresses in various crops by inducing a series of biochemical, physiological, molecular and subcellular changes in plants; (2) the tendency for seed priming to reduce the longevity of high-vigour seeds and improve the longevity of low-vigour seeds; (3) the advantages of physical methods of seed priming to enhance plant production over conventional methods based on the application of different chemical substances; (4) the various physical methods (e.g. magneto-priming and ionising radiation, including gamma rays, ultraviolet (UV) rays (UVA, UVC) and X-rays) available that are the most promising presowing seed treatments to improve crop productivity under stressful conditions; and (5) effective seed priming techniques for micronutrient delivery at planting in field crops. Seed priming as a cost-effective approach is being used for different crops and in different countries to improve yield, as a complementary strategy to grain biofortification and in genetically improved crop varieties to enhance their performance under stress conditions, including submergence and low phosphorus. Some of the challenges to the broad commercial adaption of seed priming include longevity of seeds after conventional types of priming under ambient storage conditions and a lack of studies on hermetic packaging materials for extended storage.

No abstract

The rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system is the largest agricultural production system worldwide, and is practised on 24 Mha in Asia. Many factors have threatened the long-term sustainability of conventional rice–wheat cropping systems, including degradation of soil health, water scarcity, labour/energy crises, nutrient imbalances, low soil organic matter contents, complex weed and insect flora, the emergence of herbicide-resistant weeds, and greenhouse-gas emissions. Options for improving the yield and sustainability of the rice–wheat cropping system include the use of resource-conservation technologies such as no-till wheat, laser-assisted land levelling, and direct-seeded aerobic rice. However, these technologies are site- and situation-specific; for example, direct-seeded aerobic rice is successful on heavy-textured soils but not sandy soils. Other useful strategies include seed priming, carbon trading and payment, the inclusion of legumes, and eco-friendly and biological methods of weed control. Irrigation based on soil matric potential using tensiometers can be useful for saving surplus water in direct-seeded, aerobic rice. These options and strategies will contribute to resolving water scarcity, saving labour and energy resources, reducing greenhouse-gas emissions, increasing soil organic matter contents, and improving the soil-quality index. Seed priming with various substances that supplement osmotic pressure (osmotica) is a viable option for addressing poor stand establishment in conservation rice–wheat cropping systems and for increasing crop yields. To strengthen the campaign for using resource-conservation technologies in rice–wheat cropping systems, carbon-payment schemes could be introduced and machinery should be offered at affordable prices. The persistent issue of burning crop residues could be resolved by incorporating these residues into biogas/ethanol and biochar production. Because rice and wheat are staple foods in South Asia, agronomic biofortification is a useful option for enhancing micronutrient contents in grains to help to reduce malnutrition.

Thermal stress during reproductive development and grain-filling phases is a serious threat to the quality and productivity of grain legumes. The optimum temperature range for grain legume crops is 10−36°C, above which severe losses in grain yield can occur. Various climatic models have simulated that the temperature near the earth’s surface will increase (by up to 4°C) by the end of this century, which will intensify the chances of heat stress in crop plants. The magnitude of damage or injury posed by a high-temperature stress mainly depends on the defence response of the crop and the specific growth stage of the crop at the time of exposure to the high temperature. Heat stress affects grain development in grain legumes because it disintegrates the tapetum layer, which reduces nutrient supply to microspores leading to premature anther dehiscence; hampers the synthesis and distribution of carbohydrates to grain, curtailing the grain-filling duration leading to low grain weight; induces poor pod development and fractured embryos; all of which ultimately reduce grain yield. The most prominent effects of heat stress include a substantial reduction in net photosynthetic rate, disintegration of photosynthetic apparatus and increased leaf senescence. To curb the catastrophic effect of heat stress, it is important to improve heat tolerance in grain legumes through improved breeding and genetic engineering tools and crop management strategies. In this review, we discuss the impact of heat stress on leaf senescence, photosynthetic machinery, assimilate translocation, water relations, grain quality and development processes. Furthermore, innovative breeding, genetic, molecular and management strategies are discussed to improve the tolerance against heat stress in grain legumes.