Prices are not updated to the current year to make these results comparable to Lu et al.’s study in 2003; input and output prices have changed at different rates during the past 10 years and some prices could not be recovered from Lu et al. This assumption does not affect lessons from this study.Three SV matrices for rotation, terrace techniques and land units are created using the estimation results and shown in Tables 8, 9 and 10. These tables can be used to compare the SVs between any pair of rotation types, terracing techniques or land units. Several more detailed tables can be found in Hou for those interested. The SV matrix for the 17 cropping systems is given in Table 8. The rotation types in the first row serve as references. Each value represents a movement from the system on the horizontal axis to the system along the vertical axis. For example, SV is reduced by 465.52 RMB when switching from corn to wheat and improved by 441 RMB if moving from corn to the best system, which is the CSC rotation. A3CM and FA5MC rank second. The cropping systems with PWCM and FWPM create the lowest SV. Wheat is typically low compared to rotations. The SV matrix for three terracing techniques implies that bench terracing contributes most to SV,maceta plastico cuadrada followed by spaced terracing. The cropping systems with no terraces have the least SV when all other practices are held equal.
Not surprisingly, based on the SV matrix for five types of land units , a floodplain is efficient, while very steeply sloped land has the least value. A similar set of SE matrices reinforces the same results, but is not shown here.One of the priorities of this study is to make practical recommendations for improving sustainable agricultural practices in China’s Loess Plateau to balance economic and environmental objectives. SV is computed for different agricultural systems and recorded and organized into comparison matrices. These comparison matrices can be used to compare the relative sustainability of different crops or management practices like rotations and terracing. For example, cropping systems with potatoes or wheat typically were less sustainable than systems with alfalfa and corn. A regression was also used to specify the marginal contribution of cropping system characteristics on SV or SE. Overall, the DEA/SV analysis of Lu et al.’s 2006 potential cropping systems for the region demonstrated that, all things held equal, bench terracing contributes the most to SV. SV is reduced by 465.52 RMB when switching from corn to wheat and improved by 441 RMB if moving from corn to the best system, which is the CSC rotation. On average, SV is −1661 RMB and SE is 69%. Clearly, soil erosion could be reduced without sacrifices in income if producers switched to more efficient systems. However, these results are limited to the present data and the dimensions of sustainability that were considered. Income might be affected, for example, if a change in cropping systems leads to less diversity, and therefore more exposure to the risk of disease. In contrast to other accounting approaches that make adjustments to GDP, the DEA/SV method can be used to inform policy makers, farmers, and farm managers about the sustainability of regional natural resource management decisions.
However, a limitation in the analysis is that the sustainability values are based on simulation, rather than the sustainability of current agricultural practices . Therefore, the results should be viewed in the context of potential, rather than actual, impacts.The region concerns environmentalists, ecologists, economists, agronomists and policy makers alike. As previously stated, much of the agricultural land in the region has already been converted to trees through the Grain for Green program . However, planting land to permanent forests is an extreme conservation measure that generates little economic return to farmers . Perhaps excessive erosion has been traded in for excessive conservation. Policy makers need information and ways to compare systems if they aim to realize both strong economic and social performance with sustainable use of natural resources . Combining the DEA with the SV metric allows for customizable benchmarks that can, at least in theory, facilitate a practical comparison between agricultural land management decisions. This is due, in part, to the fact that this combined DEA/SV approach accounts for the depreciation of natural capital through soil erosion and nitrogen losses, along with human capital. Policy makers can consider trade offs between economic and environmental objectives, as well as extreme solutions that focus on just the environment or just economics. In this comparison of over 2000 possible cropping systems, switching from mono-crop corn to a corn–soybean–corn rotation would generate 441 RMB/ha in SV.
When armed with this knowledge, Chinese policy makers can take steps to educate farmers about the benefits of these trade-offs. In poor areas of China, farmers may lack knowledge about advanced cropping practices. The government also can provide financial incentives to farmers to switch from unsustainable to sustainable cropping systems by subsidizing or offering technological support.Humans have reshaped the biosphere, driving rapid evolution in the species that we exploit. Agriculture stands out as a vast human alteration of biodiversity on Earth: over 12 000 years, humans have molded hundreds of wild plant species into productive crops that cover N35% of the terrestrial habitat. Domestication is a multistaged response to human-imposed selection that progresses from the increase in frequency of desirable alleles in nearly wild populations, to the formation of cultivated populations and deliberate breeding and improvement. Breeding practices have favored crop lineages that produce large, flavorful, and rapidly growing vegetative structures, fruits, and seeds, with improved disease resistance and environmental tolerance traits that manifest primarily in above ground plant tissues. However, below ground traits can be difficult for humans to evaluate during domestication and crop improvement. Thus, the evolutionary disruption of plant–microbe symbioses , that is, a decrease in the interaction of crops with beneficial soil microbiota, can go undetected. Over the past century, research on global staple crops and their associations with microbes has increased considerably. For example, the proportion of papers on agricultural staple crops with symbiosis or inoculation in the topic has nearly doubled since 2000 . Seminal work on wheat and soybean reveals different outcomes of microbial symbiosis between modern cultivars and their less domesticated or wild ancestors, with modern crops being less responsive to symbionts and exerting less robust partner choice. However, measures of symbiotic responsiveness must be viewed cautiously, because data interpreted to indicate that newer cultivars are less able to benefit from symbiosis can be driven by changes in plant performance in the symbiont-free state, as explained in Box 1. New research has expanded to diverse crop lineages, showing that reductions in symbiosis traits can be linked to evolutionary changes in plants that occur during domestication. Symbiosis traits regulate microbial colonization and infection, and can encompass a range of plant phenotypes and mechanisms, from structures in roots and other tissues that host microbes, to the molecular and physiological systems that regulate them .In natural populations, beneficial microbes are defined by their ability to generate fitness benefits for hosts that outweigh investments hosts pay to engage in symbiosis. The net benefit for a plant from a microbial symbiont will decrease if the resource a symbiont provides becomes freely available in the environment,macetero de 7 litros as can occur in agriculture. Many fungal and bacterial plant symbionts, ranging from endophytes to epiphytes, are not well characterized. Thus, here, we focus on model plant symbioses with arbuscular mycorrhizal fungi and root-nodulating bacteria to provide examples for broader and likely more complex phenomena in plant microbiomes. Benefit from costly services, such as phosphorus provisioning or symbiotic nitrogen fixation , can be inhibited or negated under fertilization if these nutrients are freely available to plants in the soil.
Similarly, drought protection offered by rhizosphere microbes can be devalued if irrigation prevents drought stress conditions. Enhanced competitive ability mediated by soil microbiota can be rendered superfluous under herbicide treatments that eliminate weeds, and microbe-mediated resistance to herbivores can be devalued if pesticides remove herbivores at no cost to the plant. Modern intensive agriculture succeeds in protecting crops and enhancing yield, but could cause agricultural plants to evolve to shunt resources away from traits that underlie symbiosis. The consequence of the evolution of symbiosis disruption in crops under fertilized conditions depend upon whether such disruption impedes crop performance under lower, more sustainable anthropogenic inputs in agriculture; thus, symbiotic disruption could be detrimental or adaptive with respect to plant performance, and might depend on local conditions . Moreover, any negative effects of the disruption of crop symbiosis traits will be compounded if agricultural practices drive declines in the overall level of cooperation in symbiont populations, as explained in Box 3. Beneficial soil microbiota have tremendous potential to improve plant health and food security. Microbes can improve plant nutrient acquisition, defense, and stress tolerance without the environmental and socioeconomic costs associated with agrichemical inputs. Understanding microbial services, the plant phenotypes and molecular mechanisms that regulate them, and the evolutionary dynamics of host–microbe interactions, are fundamental goals in evolutionary ecology. As the human population approaches 9.7 billion in 2050, requiring a 1.7- fold increase in crop yields, the vulnerability of microbial services to degradation makes the achievement of these goals an existential challenge for translational research.Distinct evolutionary mechanisms can result in symbiosis trait disruption depending on whether symbiosis traits: trade-off with agricultural traits; accumulate deleterious mutations due to the demographics of the breeding population; or are selectively neutral under agricultural conditions. A significant aspect of the evolutionary models we present later, and a key reason to explore this issue more deeply, is that the changes predicted under these models can remain undetected by growers. For instance, reduced interactions between crops and beneficial microbes during domestication can be masked by practices of growing crops in high-nutrient agricultural fields, and could be invisible to breeders who focus primarily on above ground health.The evolutionary trade-off hypothesis predicts that artificially selected shifts in plant traits, often beyond what was previously shaped by natural selection, can disrupt other plant traits if increases in one trait necessarily result in decreases in another. Physiological constraints can result in a resource allocation trade-off between yield and symbiosis. Here, crops evolve reduced symbiosis because the costs of symbiosis compete with allocation to growth and reproduction. Trade-offs can also be driven by antagonistic pleiotropy, whereby alleles that are selected under domestication express adverse effects on symbiosis functions. Here, artificial selection favoring domestication traits outweighs any selection against the reduction in symbiosis that results from these domestication traits. Irrespective of the trade-off mechanism, artificial selection could result in crops that shunt resources to early and large yield traits and sacrifice allocation to symbiosis traits. Thus, adaptation under artificial selection could increase the frequency of alleles that reduce investment in symbiosis . The devaluation of symbiont services under agriculture that we described earlier can accentuate resource allocation trade-offs between yield and symbiosis. In low-nutrient soils, where many wild crop progenitors thrive, plants benefit from the nutritional services of symbionts. However, symbiotic structures entail costs, and overproducing these structures causes growth deficits. Thus, as macronutrients become more available under fertilization, net plant benefit from symbiosis is reduced or can shift toward net cost . Under fertilization, plants often downregulate investment into symbiosis and multiple plant lineages have independently lost the ability to form symbioses , suggesting that the costs of symbiosis drive its evolutionary loss and that reduced dependence on symbiosis can be adaptive . If trade-offs drive canalized declines in symbiosis function, alleles that underlie high performance in agricultural environments are predicted to result in lower symbiosis function. Thus, alleles that confer symbiosis trait disruption could exhibit signals of positive selection. For example, alleles that alter phytohormone levels to induce earlier flowering have been favored by artificial selection in crops such as maize , but are also predicted to pleiotropically reduce colonization by AMF. Domestication alleles, could be tested for such trade-offs via forward genetics, statistical associations, or quantitative genetics. For instance, certain forms of pathogen resistance are useful under the novel intense disease pressures imposed on high-density crop monocultures.