David J. Connor

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.

An analysis is presented of the response of olive oil production and quality parameters, viz. fatty acids (palmitic, oleic and linoleic acids), phenolic compounds and oxidative stability to hedgerow spacing and orientation in 1-m wide super-high-density orchards of cv. Arbequina. Data reveal strong linear relationships between concentrations of fatty acids and internal irradiance within hedgerows, positive for palmitic and linoleic but negative for oleic acid. The result is a significant vertical trend in oil composition within hedgerows, but small to negligible differences in oil harvested from them in totality. The explanation is found in the small ranges and strongly correlated responses of individual fatty acids that together comprise 98% of oil mass. Phenolic compounds respond more widely and to higher levels of irradiance than fatty acids and did show increases in NS hedgerows grown at wide row spacing. Oxidative stability shows a similar trend in phenolic compounds. A simulation study that extended the known responses to 2-m wide hedgerows showed that the linkage between fatty acid profiles was maintained with no resultant differences in the oil composition of the total simulated oil harvest. Based on the current understanding of internal irradiance within olive hedgerows, there seems to be little opportunity to manage oil quality by orchard structure.

The impact of current calls for transformation of agriculture away from reliance on agrochemical inputs (conventional agriculture) to natural processes (organic agriculture) is gaining strength because the limited productivity of agriculture transformed in this way is unappreciated and/or ignored. Of course, it is possible to produce high yields of individual crops adequately fertilized organically or chemically, but organic fertilizers require land set aside for biological nitrogen fixation (BNF) by legumes to provide the key macronutrient nitrogen (N) on which organic production relies. The consequence is more area to produce the same amount of food and expansion of agriculture can only be done at the expense of land allocated to nature, presently in critically short supply. The current clamour to reduce animal production and eat less meat will impact negatively on the productivity of organic crops. An analysis of the productivity of organic farms reveals, using the common metric of human food energy, that equal production requires 2–3 times the land area of conventional farms. This was well established before the current post-truth era and, if not reincluded in planning, will lead to both more hunger and less land allocated to natural biodiversity and conservation. The ‘transformationists’ avoid scientific scrutiny by publishing in colourful promotional literature rather than in peer-reviewed journals. More attention is needed in the debate to bring two currently separated spheres of publication together and to include ‘land-use efficiency’, the output per unit land area, in this case human food, from an increasingly scarce resource.

Commercial extraction of nitrogen (N) from the atmosphere began soon after World War II and has provided N fertilizer that has transformed agriculture to meet, through greater crop areas and yields although with some regional shortfalls, the increasing food demand of a world population that has increased from 2 billion then to 7.6 billion in 2018. N fertilizer now provides more N input to agriculture (113 Mt N/year) than biological N fixation by legumes (33–46 Mt N/year) on which earlier agriculture relied entirely. Persistent claims over the last decade for return to organic methods, which include rejection of fertilizer N, are based on studies that erroneously claim adequate productivity to feed the world. Previous analyses, by contrast, have estimated that organic agriculture (OA) could at best support a world population of three to four billion. The problem is two-fold. First, organic crops grown in sequences with legumes or treated with N manures mostly yield less than crops grown with N fertilizer. Second, substantial areas of legumes are required to provide adequate N for required yields of non-legume crops. Recent analyses have overestimated the yield of organic crops by omitting the effect of weeds, pests and diseases, and by ignoring the land required for legumes. The result is a large overestimation of the relative productivity of OA. The effect of area is critical because, since there is little opportunity to increase cropping area beyond the current 1400 Mha, land for legumes means less land for, and consequently lower total production from, non-legume food crops. To replace 100 Mt N fertilizer/year with legumes at a net fixation of 100 kg N/ha/year would leave just 30% of cropland available for non-legumes producing a similar proportion of current yield. Even with major gains in yield, organic systems cannot feed our populous world and less so as the population increases to an expected 9.8 billion by 2050.

Inconsistent survival during winter due to freezing injury of varying severity is a major impediment to winter wheat (Triticum aestivum L.) growth and productivity. To evaluate the tolerance of different winter wheat cultivars and different organs of the same cultivar to prolonged freezing injury, 3 yr of controlled freezing experiments were performed with four cultivars under different freezing durations at the cultivars’ corresponding critical temperatures. Experimental plants in plastic pots that have hardened in the field were moved to freezing chambers for controlled freezing treatments during the winter. A highly significant relationship was observed between freezing duration and mortality for each of the different cultivars and organs. For every 1‐d increase in freezing duration at the critical temperature, plant mortality increased by 8.6, 22.3, 11.1, and 9.4% for cultivars Jing411, Nongda211, Zhengmai366, and Yanzhan4110, respectively. Within the same cultivar, tillers (15–32% d⁻¹) were less sensitive to freezing duration than younger leaves (25–35% d⁻¹) and older leaves (20–55% d⁻¹). Spike number was greatly influenced by freezing duration and the resulting death of tillers. For every 1% increase in tiller mortality, spike number per pot declined by 1.3, 2.0, 1.2, and 0.7% for cultivars Jing411, Nongda211, Zhengmai366, and Yanzhan4110, respectively. These findings indicate that reducing tiller death during winter is important for preventing extensive decreases in spike number.

Since the introduction of mechanized production in both developed and developing countries, crops and their management have undergone significant adaptation resulting in increased productivity. Historical yield increases in wheat have occurred across most regions of the world (20–88 kg ha⁻¹ year⁻¹), but climate trends threaten to dampen or reverse these gains such that yields are expected to decrease by 5–6% despite rising atmospheric CO₂ concentrations. Current and projected climatic factors are temporally and spatially variable in dryland cereal production systems throughout the world. Productivity gains in wheat in some locations have been achieved from traditional agronomic practices and breeding. Continued improvement in all cereal production regions and locations of the world requires technical advances, including closer monitoring of soils, water conservation strategies, and multiple sowing times using different crops to reduce risks. The management of disease, pests, and weeds will be an added challenge, especially in areas of higher precipitation. Excellent progress has been achieved in Asia and there is much potential in Sub-Saharan Africa. Technical solutions seem within our grasp but must be implemented in the context of variable social, economic, regulatory, and administrative constraints, providing opportunities for cross fertilization and global collaboration to meet them.