Half of the world's population-more than 3.5 billion people-depend on rice for more than 20% of their daily energy requirements. Rice productivity is under threat for several reasons, particularly the deficiency of micronutrients, such as boron (B). Most rice-based cropping systems, including rice-wheat, are facing B deficiency as they are often practiced on high pH and alkaline soils with low B contents, low soil organic matter, and inadequate use of B fertilizer, which restricts the availability, uptake, and deposition of B into grains. Farmers' reluctance to fertilize rice fields with B-due to the lack of cost-effective Benriched macronutrient fertilizers-further exacerbates B deficiency in rice-based cropping systems. Here we review that, (i) while rice can tolerate excess B, its deficiency induces nutritional disorders, limits rice productivity, impairs grain quality, and affects the long-term sustainability of rice production systems. (ii) As B dynamics in the soil varies between flooded and aerobic rice systems, different B deficiency management strategies are needed in rice-based cropping systems. (iii) Correct diagnosis of B deficiency/toxicity in rice; understanding its interaction with other nutrients including nitrogen, phosphorus, potassium, and calcium; and the availability and application of B fertilizers using effective methods will help to improve the sustainability and productivity of different rice production systems. (iv) Research on rice-based systems should focus on breeding approaches, including marker-assisted selection and wide hybridization (incorporation of desirable genes), and biotechnological strategies, such as next-generation DNA and RNA sequencing, and genetic transformations to develop rice genotypes with improved B contents and abilities to acquire B from the soil. (v) Different B application strategies-seed priming and foliar and/or soil application-should be included to improve the performance of rice, particularly when grown under aerobic conditions.

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Rising global mean temperatures open opportunities in high‐altitude production systems for temperature‐sensitive crops such as lowland rice. Currently, the cropping window for rice in higher altitudes is still narrow, and thus, genotypes that tolerate a certain degree of chilling are needed to achieve their potential yield. Final yield depends on the interaction between genotype and environmental conditions. Exposing the genotype to a wide range of environments is a way to evaluate its adaptability into an expanding cropping calendar. Over a 2‐year period, an experiment was conducted in lowland rice systems in Madagascar at two locations differing in altitude. Twenty genotypes with contrasting levels of tolerance to low temperature were sown monthly in a non‐replicated rice garden trial. Plant development was monitored and yield and yield components were determined. Yield stability across the different growing environments was investigated. While crop duration was affected by sowing dates and altitude, yield was mainly determined by sowing date. Panicle number per m2 and number of spikelets per panicle were the most limiting factors for yield potential in mid‐altitude, while in high altitude, yield was mainly limited by spikelet fertility. Resulting cropping calendar and genotype recommendations are discussed.

Nitrogen (N) is one of the main nutrients that drive rice grain yield and is intensely managed especially in lowlands under irrigated conditions. A set of experiments was conducted in mid‐ and high‐altitude sites in Rwanda to investigate the response of five genotypes under different sowing dates and different N management. Genotype grain yields were higher and more stable at mid‐altitude across sowing dates. N rates strongly affected grain yield at mid‐altitude (p < .0001), but not at high altitude. Postponing basal N had positive effects on yield and yield components in both sites, with more pronounced effects at high altitude. Increasing N rate beyond 120 kg/ha led to a decrease in percentage of panicles per tiller and spikelet fertility and a decrease in grain yield due to excessive tillers at both high altitude and mid‐altitude. Thus, basal N application should be recommended at high altitude and the increase in N rate up to 120 kg/ha at mid‐altitude. A strict observation of recommended planting date should be followed at high altitude, and the use of cold‐tolerant genotypes is encouraged.

Background: In flooded rice fields, root zone temperatures (RZT) are buffered by the ponded water layer. With global warming, a higher frequency of hot days and hot nights, and the introduction of water‐saving irrigation technologies, RZT are likely to vary more widely, particularly between night and day.Aim: It is not known how this will affect nutrient uptake of rice, particularly if the climate‐driven transpirational demand increases simultaneously, since nutrient uptake at least partly depends on water uptake.Methods: We investigated the effects of day and night RZT on water and nutrient uptake and nitrogen (N) metabolism under low and high vapor pressure deficit (VPD). Plants of two rice varieties (IR64 and NU838) were grown hydroponically at three root temperature levels (19, 24, and 29°C). For a period of seven days, fresh weight of the plants, nutrient contents of the nutrient solution (, , , K+), and water uptake were measured both at the end of the light period and at the end of the dark period. Nitrate reductase (NR), glutamine synthetase (GS), and amino acid (AA) concentrations in the youngest fully developed leaves were examined on the last day and night of the experiment.Results: The share of day and night uptake of and depended on RZT, whereas K+ uptake was higher during the day independent of RZT. Under low VPD, uptake rate did not differ between day and night, however, under high VPD, the uptake of varied between varieties and RZTs. Water uptake of the plants was strongly influenced by VPD, but not by RZT. In contrast, nutrient uptake was hardly influenced by VPD and did not correlate with water uptake, but linearly increased with RZT with an optimum temperature for nutrient uptake above 29°C. This increase was larger for and than for and K+ shifting the nutrient requirements of rice. While the increase of nutrient uptake per °C did not differ between varieties under low VPD, IR64 showed a greater increase in nutrient uptake to RZT at day‐time, whereas NU838 showed a greater increase at night‐time under high VPD. The activities of NR and GS seemed to respond to the total daily N uptake rather than to different uptake rates during day or night, while AA concentration was strongly correlated to N uptake during the day.Conclusions: With an optimum RZT for nutrient uptake above 29°C, rice plants could benefit from temperature increase caused by either different water management strategies or climate change if fertilizer management was adapted to the new, shifted requirements.

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Feeding the future world population requires increased crop production. Here, we investigate the intensification option of increasing production by increasing cropping intensity and choice of varieties with different crop duration. We developed a model to generate, compare and visualise opportunities for single/double/triple cropping systems consisting of irrigated rice and optionally a vegetable. The model was applied in a case study in the Senegal River valley. Results showed that with appropriate choice of sowing dates, severe cold sterility in rice can be avoided, also in rice–rice crop rotations. At optimal sowing dates, simulated total long term average potential yields of single, double and triple cropping yields were 10.3, 19.0 and 18.9 t/ha respectively (total of 1,2 and 3 yields). With a hypothetical completely cold tolerant variety, yields could increase to 11.2, 20.2 and 20.9 respectively. Simulated Triple crop yields are hardly any higher than those of a double crop with two medium duration varieties. Delay in sowing due to late availability of resources (machinery, irrigation water allocation within a scheme, credits for pump fuel) is a known problem in the region. Therefore we also simulated how much delay was possible (width of the sowing windows) whilst still allowing for double cropping. We found enough delay was possible to allow for a rice–rice or a rice-vegetable crop. A rice-rice-vegetable triple cropping system would only be possible without delays and with a very short duration vegetable of 2 months. Most promising options to increase production are through shifting the sowing date to facilitate double cropping, adoption of medium duration varieties and breeding for cold tolerant varieties. (Résumé d'auteur

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