Studies that quantify the contribution of genetic improvement to crop yields typically rely on comparisons of old cultivars grown side-by-side with more recent ones. This approach, however, does not allow to distinguish gains in yield potential versus maintenance breeding that aims to keep cultivars adapted to the evolving biophysical environment, including pests, diseases, and climate. Here we show an overall wheat yield improvement of 73 kg ha-1 y-1 based on direct comparison of modern cultivars against older 'check' cultivars using data from multi-environment trials from Argentina, France, United Kingdom, and United States. However, almost half of this improvement (33 kg ha-1 y-1) is attributable to maintenance breeding needed to counteract the yield erosion of older cultivars, and the other portion (40 kg ha-1 y-1) can be associated with the higher yield potential of modern cultivars. We conclude that comparison of new versus old cultivars under current conditions leads to an overestimation of genetic gains in yield potential.

The global food system relies on crop production in limited number of regions around the world. The South American Pampas region is a major breadbasket due to favorable weather and fertile soils for reliable crop production and capacity to produce a large grain and oilseeds surplus. However, for decades, nutrient inputs have been much lower than in other regions, leading to heavy “mining” of soil nutrient stocks. Here we evaluated the impact of soil degradation using soil and crop surveys and field-level data sets from across the Pampas. Compared to a balanced nutrient input management regime, current nutrient management reduces total grain output by 41 million tons and farmer profit by US$ 6.3 billion annually, which leads to a severe decline in soil organic carbon and nutrient stocks. We conclude that the region must improve its nutrient management to retain its role as a highly productive, global breadbasket while preserving soil health for future generations.

Potassium (K) has received little attention as a potential yield-limiting factor in cropping systems. Here we investigated the K status in intensive cereal cropping systems in Indonesia, which are representative of many other Southeast Asian countries. Our analysis included nutrient input-output balance, leaf nutrient status, long- and short-term fertilizer trials, and farmer surveys. We revealed that soil K levels alone are insufficient to meet plant requirements, and current fertilizer applications are inadequate to prevent K deficiencies and large negative annual soil K balances in farmer fields (average -62 kgK ha-1). On-farm fertilizer trials indicated that nearly 80% of rice crops and 70% of maize crops achieved higher yields with the application of K fertilizer. Addressing K limitations will require an enhanced capacity to predict crop responses to K fertilizer, together with long-term, flexible fertilizer and crop residue management strategies. Furthermore, similar K limitations have probably emerged in other regions globally due to intensive cropping with insufficient K replenishment, which must be addressed to close yield gaps on existing farmland.

Rice yields in Uruguay have increased rapidly (159 kg-1 ha-1 y-1) between 1990 and 2013. There is evidence, however, of an incipient yield plateau in recent years. The aim of this study was to determine if the recent slowdown in yield gains is because average yield (Ya) has approached the yield potential (Yp) ceiling, which makes it increasingly difficult for farmers to sustain further yield gains. We followed the methodology developed by the Global Yield Gap Atlas to estimate Yp and associated yield gaps for irrigated rice supported by data from high-yield experiments to calibrate the rice simulation model Oryza (v3). Subsequently, the model was used to simulate Yp using long-term daily weather data from seven locations, representing 90 % of total rice area in Uruguay. The exploitable yield gap (Yeg) was calculated as the difference between 80 % of Yp and Ya. Estimated national average Yp was 13.9 Mg ha-1, with relatively small variation across sites, from 13.1 to 15.1 Mg ha-1. Average Ya was 8.3 Mg ha-1, ranging from 7.9 to 8.5 Mg ha-1 across sites, and representing 60 % of Yp. Our analysis suggests there is still room to further increase rice yields in Uruguay, because the Yeg is 2.8 Mg ha-1, which means the current yield plateau is not due to Ya approaching Yp, as has occurred in other high-yield irrigated rice systems in China and California, USA. The approach followed here can help determine whether yield plateaus are occurring due to a small Yeg or other factors.

Context: Intensive rice-maize sequences in Southeast Asia can include up to three crop cycles per year. Indonesia is the third and fifth largest rice and maize producing country worldwide, and domestic demand for both crops will increase in the future. Novel, cost-effective and less time-consuming approaches are needed to identify causes of yield gap at national level. Objectives: Here, we propose a farmer data-driven approach to prioritize investment in agricultural research and development (AR&D) programs. Methods: We collected data on yield, management practices, and socioeconomic variables from 1,147 small-holders' fields in intensive rice and maize cropping systems, from 2017 to 2018, across ten provinces in Indonesia, which include a wide range of landscape positions (upland, lowland, tidal), water regimes (irrigated and rainfed), and cropping intensities (from single to three cycles per year on the same piece of land). Separate data were available for each rice and maize cycle included in the annual crop sequence. We used conditional inference trees, random forest regression, and comparisons among high-versus low-yield fields to identify key agronomic and socioeconomic factors explaining yield variation. Results: For a given field and crop species, there was a significant positive correlation between yield in one season and that in subsequent seasons. In contrast, there was poor correlation between rice and maize yields in cropping systems including both crops. Socio-economic factors such as years of farming experience and access to extension services and inputs explain variation in average yield gap across provinces. In turn, agronomic factors such as nutrient input rates, splits and timing, establishment date, and pest control, explained yield gaps in farmer fields. Overall, these findings were not consistent with expectations from local researchers about on-farm yield constraints. Conclusions: Our study shows that a modest investment to gather farmer survey data, together with robust spatial frameworks to guide data collection, proper statistical methods to analyze the data, and crop modeling to es-timate yield potential, can help identify yield constraints for areas representing millions of hectares of rice and maize. Significance: Our study provides useful information for guiding investments in AR&D programs at national and sub-national level for improving crop production by closing current yield gaps.

Potassium (K) has received less attention than nitrogen (N) and phosphorous (P) as a potential yield-limiting factor in cropping systems. Here we investigated the current K limitation in intensive cereal cropping systems of Southeast Asia based on nutrient balances, leaf nutrient status, long- and short-term fertilizer trials, and farmer surveys. We found that soil K alone cannot meet plant requirements and current fertilizer application is insufficient to avoid plant K deficiencies and large negative soil K balances in farmer fields. Removing the K limitation requires improved capacity to predict response to K fertilizer together with long-term, flexible fertilizer and crop straw management strategies. It is likely that similar K limitations have emerged in other world regions as a result of decades of intensive cropping with insufficient replenishment of potassium, which represent headwinds to closing yield gaps on existing farmland.

Perennial grain crops have been proposed as environmentally sustainable alternatives to annual grain crop systems that currently dominate the world's major breadbaskets. Proponents emphasize the potential of perennial grains to mimic natural systems and thereby reduce soil erosion, nutrient losses, and degradation of soil quality although need for adequate grain yield is also recognized as a prerequisite for success. Here we assess progress since 2005 (16 y) towards development of perennial grain systems with sufficient productivity to be seen as competent alternatives to annual wheat on the prairies and plains of North America and Australia. Based on reports published in refereed journals, we see little evidence that yield of Intermediate Wheatgrass or perennial wheats have improved to the point they are viable alternatives. Slow progress is attributed to lack of minimum grain yield targets for economic viability, lack of designated target regions where perennial grains are most likely to be competitive against annuals, selection methods that focused on components of yield rather than yield per se (i.e. on an area basis), and relatively small R & D investment compared to resources given to genetic and agronomic improvement of major annual grain crops. Given current status, we conclude that perennial grains will require substantial R & D investment and several decades if they are to achieve sufficient yield potential and yield persistence to become more than a niche crop for upscale health food markets in wealthy countries.

Quantitative understanding of factors driving yield increases of major food crops is essential for effective prioritization of research and development. Yet previous estimates had limitations in distinguishing among contributing factors such as changing climate and new agronomic and genetic technologies. Here, we distinguished the separate contribution of these factors to yield advance using an extensive database collected from the largest irrigated maize-production domain in the world located in Nebraska (United States) during the 2005-to-2018 period. We found that 48% of the yield gain was associated with a decadal climate trend, 39% with agronomic improvements, and, by difference, only 13% with improvement in genetic yield potential. The fact that these findings were so different from most previous studies, which gave much-greater weight to genetic yield potential improvement, gives urgency to the need to reevaluate contributions to yield advances for all major food crops to help guide future investments in research and development to achieve sustainable global food security. If genetic progress in yield potential is also slowing in other environments and crops, future crop-yield gains will increasingly rely on improved agronomic practices.

Adequate crop yields to feed 7.8 billion people today, and nearly 10 billion by mid-century (Vollset et al. 2020), depend on large amounts of nitrogen (N) input, which in turn represent an inherent weakness in our global food production system.The challenge has nothing to do with N supply as that is virtually unlimited.Nearly 80% of the atmosphere is composed of N 2 , a relatively inert gas, that can be converted to reactive N forms (mostly nitrate, NO 3 -

Food security interventions and policies need reliable estimates of crop production and the scope to enhance production on existing cropland. Here we assess the performance of two widely used 'top-down' gridded frameworks (Global Agro-ecological Zones and Agricultural Model Intercomparison and Improvement Project) versus an alternative 'bottom-up' approach (Global Yield Gap Atlas). The Global Yield Gap Atlas estimates extra production potential locally for a number of sites representing major breadbaskets and then upscales the results to larger spatial scales. We find that estimates from top-down frameworks are alarmingly unlikely, with estimated potential production being lower than current farm production at some locations. The consequences of using these coarse estimates to predict food security are illustrated by an example for sub-Saharan Africa, where using different approaches would lead to different prognoses about future cereal self-sufficiency. Our study shows that foresight about food security and associated agriculture research priority setting based on yield potential and yield gaps derived from top-down approaches are subject to a high degree of uncertainty and would benefit from incorporating estimates from bottom-up approaches.

Abstract Future rice systems will need to produce more grain while minimizing the environmental impact. A key question is how to orient agricultural research & development (R&D) programs at national to global scales to maximize the return on investment. Here we assess yield gap and resource-use efficiency (including water, pesticides, nitrogen, labor, and energy) across 32 rice cropping systems, together accounting for 88% of global rice production. We show that achieving high yields and high resource-use efficiencies are not conflicting goals. Most cropping systems have room for increasing yield, resource-use efficiency, or both. In aggregate, current total rice production of these systems can be increased by 36%, and excess nitrogen almost eliminated, by focusing on a relatively small number of cropping systems with large yield gaps and/or poor resource-use efficiencies. This study provides essential strategic insight for prioritizing national and global agricultural R&D investments to ensure adequate rice supply while minimizing negative environmental impact in coming decades.

Future rice systems must produce more grain while minimizing the negative environmental impacts. A key question is how to orient agricultural research & development (R&D) programs at national to global scales to maximize the return on investment. Here we assess yield gap and resource-use efficiency (including water, pesticides, nitrogen, labor, energy, and associated global warming potential) across 32 rice cropping systems covering half of global rice harvested area. We show that achieving high yields and high resource-use efficiencies are not conflicting goals. Most cropping systems have room for increasing yield, resource-use efficiency, or both. In aggregate, current total rice production could be increased by 32%, and excess nitrogen almost eliminated, by focusing on a relatively small number of cropping systems with either large yield gaps or poor resource-use efficiencies. This study provides essential strategic insight on yield gap and resource-use efficiency for prioritizing national and global agricultural R&D investments to ensure adequate rice supply while minimizing negative environmental impact in coming decades.

U.S. crop producers are faced with increasing challenges to maintain productivity growth and profit while also addressing environmental concerns about nutrient losses and climate change. Because progressive producers must optimize a large number of strategic and tactical crop and soil management decisions, conventional, replicated field experiment designs with two or three management treatment factors are not up to the task. It is therefore important to utilize crop performance evaluation methods that more efficiently identify those management factors with greatest impact on yield and input requirements, and their interactions with other management practices, across the wide range of soil and climates that comprise our major crop‐producing regions. Earn 1 CEU in Crop Management by reading this article and taking the quiz at https://bit.ly/3iURzWv. View all CEUs online at https://web.sciencesocieties.org/Learning‐Center/Courses.

Urbanization has appropriated millions of hectares of cropland 1 , and this trend will persist as cities continue to expand 2 . Here we estimated the substitution cost by comparing the yield potential between the converted and newly cultivated land as determined by climate and soil properties. To do so, we used robust spatial upscaling techniques, well-validated crop simulation models, and soil, climate, and cropping system databases 3–5 , focusing on populous countries exhibiting high rates of land conversion. We found that productivity of new cropland is substantially lower than the land it replaces, which means that projection of food production potential must account for expected cropland loss to urbanization and the lower productivity of new land that replaces it. Policies that protect existing farmland from urbanization would relieve pressure on expansion of agriculture into natural ecosystems and reduce the associated greenhouse gas emissions and biodiversity loss.

Hundreds of millions of smallholders in emerging countries substantially overuse nitrogen (N) fertilizers, driving local environmental pollution and global climate change. Despite local demonstration-scale successes, widespread mobilization of smallholders to adopt precise N management practices remains a challenge, largely due to associated high costs and complicated sampling and calculations. Here, we propose a long-term steady-state N balance (SSNB) approach without these complications that is suitable for sustainable smallholder farming. The hypothesis underpinning the concept of SSNB is that an intensively cultivated soil-crop system with excessive N inputs and high N losses can be transformed into a steady-state system with minimal losses while maintaining high yields. Based on SSNB, we estimate the optimized N application range across 3,824 crop counties for the three staple crops in China. We evaluated SSNB first in ca. 18,000 researcher-managed on-farm trials followed by testing in on-farm trials with 13,760 smallholders who applied SSNB-optimized N rates under the guidance of local extension staff. Results showed that SSNB could significantly reduce N fertilizer use by 21 to 28% while maintaining or increasing yields by 6 to 7%, compared to current smallholder practices. The SSNB approach could become an effective tool contributing to the global N sustainability of smallholder agriculture.

Food security interventions and policies need reliable estimates of actual crop production and the scope to enhance production on existing cropland. We assess the performance of two widely used “top-down” gridded frameworks (GAEZ and AgMIP) versus an alternative “bottom-up” approach that estimates extra production potential locally, for a number of representative sites, and then upscales the results to larger spatial scales (GYGA). Our results show that estimates from top-down frameworks are alarmingly unlikely, with estimated potential production being lower than current production at some locations. The consequences of using these coarse estimates to predict food security are illustrated by an example from sub-Saharan Africa. Our study shows that current foresights on food security, land use, and climate change and associate priority setting on AR&D based on yield potential and yield gaps derived from top-down approaches are subject to a high degree of uncertainty and would benefit from incorporating estimates from bottom-up approaches.

CONTEXT: The nitrogen (N) balance provides an indication of the risk for N losses into the environment. Previous studies have shown large variation in N balance among producer maize fields in the US Corn Belt, even within the same region and year. However, little is known about the soil and management factors explaining variation in N balance and to what extent the influence of these factors on N balance occurs via grain yield, N inputs, or both. OBJECTIVE: This study aimed to disentangle interactions among yield, management practices, and soil factors to identify which have the greatest influence on N balance in producer maize fields in Nebraska (USA). METHODS: The database used contains yield and management records from 311 producer irrigated and rainfed fields sown with maize for two years (2010-2011). The N balance was estimated as the difference between N inputs (from fertilizer and applied irrigation) and grain N removal. Random forest regression and path analysis were used to assess the influence of soil and management factors on the N balance via either grain yield or N inputs for irrigated and rainfed fields. RESULTS AND CONCLUSIONS: Analysis based on combination of advanced statistics showed that soil organic matter (SOM), seeding rate, sowing date, and in-season N sidedress influenced N balance, mostly via N inputs application and, to a lesser degree, grain yield. In many cases, producer risk behavior explained the relationship between N balance and soil and management factors. For example, N application was higher in fields that have lower SOM or received in-season N sidedress, without any yield advantage. The findings suggest that efforts are needed to help producers manage N inputs more efficiently and deal with the associated risks. SIGNIFICANCE: Our study performed a novel field level assessment of factors influencing N balance which provides useful information in prioritization of agricultural research and extension programs to avoid large N balances and associated negative environmental impact.

Urbanization has appropriated millions of hectares of cropland, and this trend will persist as cities continue to expand. We estimate the impact of this conversion as the amount of land needed elsewhere to give the same yield potential as determined by differences in climate and soil properties. Robust spatial upscaling techniques, well-validated crop simulation models, and soil, climate, and cropping system databases are employed with a focus on populous countries with high rates of land conversion. We find that converted cropland is 30–40% more productive than new cropland, which means that projection of food production potential must account for expected cropland loss to urbanization. Policies that protect existing farmland from urbanization would help relieve pressure on expansion of agriculture into natural ecosystems.

Reducing nitrous oxide (N2O) emissions from agriculture is critical to limiting future global warming. In response, a growing number of food retailers and manufacturers have committed to reducing N2O emissions from their vast networks of farmer suppliers by providing technical assistance and financial incentives. A key challenge for such companies is demonstrating that their efforts are leading to meaningful progress toward their climate mitigation commitments. We show that a simplified version of soil surface nitrogen (N) balance-or partial N balance-the difference between N inputs to and outputs from a farm field (fertilizer N minus crop N), is a robust indicator of direct N2O emissions from fields with maize and other major rainfed temperate-region crops. Furthermore, we present a generalized environmental model that will allow food-supply-chain companies to translate aggregated and anonymized changes in average N balance across their supplying farms into aggregated changes in N2O emissions. This research is an important first step, based on currently available science, in helping companies demonstrate the impact of their sustainability efforts.