Specifically, the effect of flood water application frequency on mineralization of organic N to inorganic forms should be investigated to assess the full N loading amount to groundwater under AgMAR. Although our study was exclusively focused on the impact of AgMAR on groundwater nitrate quality, we believe these findings to be applicable to other similar settings, such as wetlands, floodplains and managed recharge basins. Natural settings such as floodplains and riparian corridors experience ponded water for much of the year and are considered to be denitrification hot spots . These systems are typically associated with higher DOC and therefore, oxygen consumption is expected to occur at much higher rates than our model setup. This rapid decline in oxygen results in reducing conditions that are favorable to denitrification and efficient nitrate removal. Our model simulations of different hydraulic loadings further demonstrate that changing hydrologic regimes in natural and managed landscapes can substantially alter nitrate consumption versus export from these landscapes. The Earth’s human population is expected to increase from the current 6.7 billion to 9 billion by 2050. To feed the growing population,growing blackberries in containers and the 70% increase in the demand for agricultural production that is expected to accompany this increase, a broad range of improvements in the global food supply chain is needed.
For example, sustainable agricultural intensification will be important because maintaining current per capita food consumption with no increase in yield, and no decrease in post-harvest and food waste, would necessitate a near doubling of the world’s cropland area by 2050. However, because most of the Earth’s arable land is already in production and what remains is being lost to urbanization, salinization, desertification, and environmental degradation, cropland expansion is not a viable approach to food security. Furthermore, because substantial greenhouse gases are emitted from agricultural systems, expansion of cropland would also substantially contribute to carbon mitigation . Thus, the development and deployment of high-yielding crop varieties will make a vital future contribution to sustainable agriculture because it does not rely on expanding cropland. Water systems are also under severe strain across the world. The fresh water available per person has decreased 4-fold in the last 60 years. Of the water that is available for use, about 70% is already used for agriculture. Many rivers no longer flow all the way to the sea; 50% of the world’s wetlands have disappeared and major groundwater aquifers are being mined unsustainably, with water tables in parts of Mexico, India, China, and North Africa declining by as much as 1 meter per year. Thus, increased food production must largely take place on the same land area while using less water. The need for land and water for food production must compete with demands for ecosystem preservation and biomass production. Compounding the challenges facing agricultural production are the predicted effects of climate change. As the sea level rises and glaciers melt, low lying croplands will be submerged and river systems will experience shorter and more intense seasonal flows, causing more flooding.
Yields of our most important food, feed, and fiber crops decline precipitously at temperatures much above 30uC, so heat and drought will also increasingly limit crop production. In addition to these environmental stresses, losses to pests and diseases are also expected to increase. Much of the loss caused by these abiotic and biotic stresses, which already result in 30%–60% yield reductions globally each year, occur after the plants are fully grown; a point at which most or all of the land and water required to grow a crop has been invested . For this reason, a reduction in losses to pests, pathogens, and environmental stresses is equivalent to creating more land and more water . Another important opportunity for increasing food availability is to reduce the amount of food wasted before and after it reaches the consumer . Substantial changes in diet through education and/or technological innovation— while difficult—could also make up a good deal of the shortfall in feeding the world’s population. For example, a reduction in meat consumption would contribute to increasing the food supply, because 1 hectare of land can produce rice or potatoes for 19–22 people per year whereas the same area will produce enough meat for only 1–2 people. Food security, as defined by the Food and Agriculture Organization of the United Nations, ‘‘exists when all people, at all times, have physical, social and economic access to sufficient safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life’’. Currently, there are 925 million people who are undernourished , and nearly all live in less developed countries.
The long-term effects of malnutrition include stunted growth, learning disabilities, poor health, and chronic disease in later life. Growing more staples that are deficient in essential vitamins and minerals will not tackle health problems caused by nutrient poor diets. In this Essay, I discuss how discoveries in plant genetic and genomics research can be translated to create new crops and cropping systems that more efficiently use finite resources and that can enhance the quality and quantity of food production. Each strategy must be evaluated in light of its environmental, economic, and social impacts—the three pillars of sustainable agriculture .The term plant translational research broadly refers to basic research discoveries that are applied to agronomic improvement. For example, discoveries that reveal basic mechanisms of inheritance in a model plant, such as the genetically tractable plant Arabidopsis, can be applied to crops to accelerate plant breeding . Translational research also encompasses a strategy that has worked well in one crop and then was applied to another. Although not covered in this Essay, translational research also includes non-genetic approaches to improving crop yield or quality emanating from fundamental research on plants, such as research into crop water use efficiency.For 10,000 years, we have altered the genetic makeup of our crops, first through primitive domestication and, in the last 300 years, using more sophisticated approaches. For example, in the 1920s, the first hybrid seeds were commercialized. Hybrids inherit their agronomically useful traits, such as high yield, disease resistance,square pot and environmental stress tolerance, from two genetically distinct parents. Although seeds produced from hybrids can be replanted, they do not have the same combination of beneficial traits as their hybrid parents. For this reason, many farmers who can afford it purchase new hybrid seed each planting season. For farmers who cannot afford hybrid seed or who do not have access to them, it is critical that they have access to improved seed that maintains their parents’ advantageous traits when self-pollinated. Other genetic improvements include mutagenesis—the introduction of random mutations by chemical treatment or radiation, and the interbreeding of related species. Familiar examples of crops generated through inter specific hybridization include many citrus varieties, such as orange varieties, lemon, lime, and grapefruit. The use of wild species as donors of agronomically important traits has also been important to the success of global agriculture. Today virtually everything we eat is produced from seeds that have been genetically altered in one way or another using these well-established.In MAS, researchers first identify the genetic ‘‘fingerprint’’ of the genes that they would like to move from one variety to another, which are usually associated with a desirable trait. Then, two varieties with the desired traits are cross-pollinated, and the breeder identifies those offspring that carry the desirable genetic fingerprint, and eliminates those that don’t. The process is then repeated. The advantage of MAS relative to other established plant breeding techniques is that researchers can screen for varieties with the preferred genetic makeup without the need of large field trials, saving both time and labor. Crops developed through MAS have fewer genetic changes relative to conventionally bred crops because a breeder can track the desired genotype and eliminate undesirable genes at non-targeted loci. For these reasons, the MAS technique is a powerful method for introducing into crop plants traits from their wild relatives and from ‘‘primitive’’ varieties , which are available from more than 1,700 seed banks worldwide.
For example, the development of a new variety of submergence tolerant rice , relied on the existence of an Indian land race called FR13A . Although rice can withstand shallow flooding, most rice varieties will die if completely submerged for more than a few days. In Bangladesh and India, four million tons of rice, enough to feed 30 million people, is lost each year to flooding . Using markers found to be linked to the Sub1 locus , our team isolated the Sub1 genomic region, which facilitated the development of additional markers . These markers allowed breeders to use MAS to introduce Sub1 into a wide range of rice varieties favored by farmers, while at the same time minimizing the introduction of undesirable traits linked to submergence tolerance in the FR13A donor. The new Sub1 rice varieties are popular in South and Southeast Asia because they are 3-fold higher yielding during periods of flood compared to conventional rice varieties. Currently, many such MAS projects are underway to facilitate the exploration of the genetic variability in our existing food crops to advance crop resilience in the face of the changing climate, pests, and disease.‘‘What has long appeared to be simply the agent of a bothersome plant disease is likely to become a major tool for the genetic manipulation of plants: for putting new genes into plants and thereby giving rise to new varieties with desired traits,’’ wrote acclaimed scientist Mary Dell Chilton in 1983. Today, more than 30 years later, we can see how the basic research of Chilton, Marc van Montagu, Jeff Schell, and their colleagues, who elucidated the molecular mechanisms with which the bacterial pathogen Agrobacterium tumefaciens transfers DNA to plant hosts, has been translated to real-world application—the genetic engineering of plants. In 2012, genetically engineered crops were grown on almost 170 million hectares in 29 countries. To understand why some farmers have embraced GE crops and how they benefit the environment , consider Bt cotton, which contains a bacterial protein called Bt that kills pests, such as the cotton boll worm, without harming beneficial A more recent technology, called genome editing, which makes it possible to precisely alter DNA sequences in living cells, is expected to lead to new crop varieties in the near future . In this technique, targeted double-strand DNA breaks are introduced in the genome at or near the site where a DNA sequence modification is desired using sequence specific nucleases. The repair of the break can be used to introduce specific DNA sequence changes, DNA deletions, or even serve as an insertion site for arrays of transgenes. Genome editing can thus be used to introduce genetic variation without transgenesis, and can even be used to recreate naturally occurring mutations into elite varieties of crops. For this reason, some scientists and farmers believe that crops generated through this technology will prove to be more socially acceptable in Europe and elsewhere than those generated by genetic engineering. As discussed in the accompanying essay , genome editing has been used to engineer rice for resistance to the bacterial pathogen, Xanthomonas oryzae pv. oryzae. Researchers created mutations in the promoter of a rice sucrose-efflux transporter gene, which is targeted by a pathogen effector . These mutations, which are mostly DNA deletions, eliminated the transcriptional induction required for pathogen virulence, rendering the plant resistant.Another technique for introducing genetic variation is induced mutagenesis through chemical or radiation treatment . A recent variation on mutagenesis, called Targeted Induced Local Lesions in Genomes , facilitates the identification and deployment of gene variants that encode agronomically important traits. This approach has been particularly useful for improving understudied crops. For example, melon variants have been identified through TILLING that have improved shelf life and those with unisexual flowers, traits that can enhance productivity in India. Another example is the identification of acyanogenic sorghum variants that can be used as improved animal fodder. Genetically improved seed, whether derived from conventional genetic modification or newly developed technologies such as genome editing, must be integrated into ecologically based farming systems to maximize their impact on enhancing sustainable agriculture and food security.