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Increasing density is an effective way to enhance wheat (Triticum aestivum L.) yield under limited cultivated areas. However, the physiological mechanisms underlying the reduction in grain weight when density increased are still unclear. Three field experiments were conducted during the 2014–2019 growing seasons to explore the physiological mechanisms by which polyamines affect grain weight formation. The results showed that when wheat planting density exceeded 450 × 104 seedlings ha−1 and 525 × 104 seedlings ha−1, wheat yield tended to decrease. Compared to moderate density (DM, 450 × 104 seedlings ha−1), the filling rate of inferior grains was reduced before 25 days after anthesis (DAA) and the active filling period was shortened by 6.4%–7.4% under high density (DH, 600 × 104 seedlings ha−1), resulting in a loss of 1000‐grain weight by 5.4%–8.1%. DH significantly reduced sucrose and starch content in inferior grains at the filling stage. Meanwhile, DH inhibited the activity of key enzymes involved in polyamine synthesis [SAMDC (EC 4.1.1.50) and SpdSy (EC 2.5.1.16)] and induced the activity of ethylene (ETH) precursor synthase, resulting in a significant decrease in endogenous spermidine (Spd) content in inferior grains, but a significant increase in ETH release rate. Post‐flowering application of exogenous Spd increased the accumulation of sucrose and starch in the inferior grains and positively regulated the filling and grain weight of the inferior grains, whereas exogenous ETH had a negative effect. Overall, Spd may affect wheat grain weight at high planting density by promoting the synthesis of sucrose and starch in inferior grains. [ABSTRACT FROM AUTHOR]

Drought stress poses a serious threat to grain formation in wheat. Nitrogen (N) plays crucial roles in plant organ development; however, the physiological mechanisms by which drought stress affects plant N availability and mediates the formation of grains in spikes of winter wheat are still unclear. In this study, we determined that pre-reproductive drought stress significantly reduced the number of fertile florets and the number of grains formed. Transcriptome analysis demonstrated that this was related to N metabolism, and in particular, the metabolism pathways of arginine (the main precursor for synthesis of polyamine) and proline. Continuous drought stress restricted plant N accumulation and reallocation rates, and plants preferentially allocated more N to spike development. As the activities of amino acid biosynthesis enzymes and catabolic enzymes were inhibited, more free amino acids accumulated in young spikes. The expression of polyamine synthase genes was down-regulated under drought stress, whilst expression of genes encoding catabolic enzymes was enhanced, resulting in reductions in endogenous spermidine and putrescine. Treatment with exogenous spermidine optimized N allocation in young spikes and leaves, which greatly alleviated the drought-induced reduction in the number of grains per spike. Overall, our results show that pre-reproductive drought stress affects wheat grain numbers by regulating N redistribution and polyamine metabolism. [ABSTRACT FROM AUTHOR]

Supplemental irrigation under a ridge-furrow (RF) cropping system is a valuable cropping practice that balances resource efficiency and high crop yield. However, the effects of nitrogen management on crop growth, yield formation, and economic benefits under RF systems have not been clearly investigated. In this study, the experiment was designed with three experimental factorials, including three cropping systems (RF, RF cropping with 80 mm irrigation; TF1, traditional flat cropping with 200 mm irrigation; and TF2, traditional flat cropping with 80 mm irrigation), two nitrogen application rates (NL, 180 kg N ha−1; NH, 240 kg N ha−1), and two fertilizer application models (B, all nitrogen fertilizers were applied basally at the pre-sowing stage; BT, nitrogen fertilizer was applied at both the pre-sowing and jointing stages at a ratio of 1:1). A two-year field experiment was conducted to investigate the effects of nitrogen fertilizer management on wheat yield, water and nitrogen utilization, and economic benefits under the RF cropping system. The results showed that the RF system significantly increased the soil moisture content and improved the water productivity (WP) and grain yield of wheat. Nitrogen reduction (NL) under the RF system did not affect the water use of the wheat compared with traditional high nitrogen application (NH) but increased the nitrogen uptake and fertilizer productivity of the wheat. Although NL led to a reduction in aboveground dry matter accumulation, it did not significantly affect the yield of wheat but increased the net income of wheat cultivation. Under NL conditions, the BT nitrogen application model promoted nitrogen uptake in wheat and ameliorated the reduction in grain protein content due to plastic film mulching, and this model is an integrated planting practice that trades off wheat yield and quality. These findings suggest that NLBT is a promising and recommendable cropping practice under RF systems considering resource utilization, high yield and quality, and economic efficiency. [ABSTRACT FROM AUTHOR]

BACKGROUND: Ridge–furrow mulching farming systems (RFMs) aim to increase field productivity and improve water use efficiency. To explore environment‐friendly and efficient farming systems is a central aspect of rainfed wheat field management in Kenya where rainfall utilization is at a low level. We introduced RFMs (including plastic film and grass straw mulching) to semiarid Kenya to evaluate the effects on field productivity, rainwater utilization, soil quality and economic profitability using old and modern wheat cultivars from 2012 to 2013. RESULTS: Across the cultivars, the RFMs increased grain yield, aboveground biomass and water use efficiency by 74–163%, 36–104% and 89–273%, respectively, compared with conventional flat planting (control). RFMs significantly shortened the vegetative period while prolonging the reproductive period. The net economic output under RFMs was 74–165% higher than that of the control. Grass straw mulching achieved the highest economic output to input ratio, almost 45% higher than plastic film mulching, despite the former harvested only 82% of the maximum field productivity of the latter. Compared with the control, grass straw mulching promoted the contents of soil organic carbon, total nitrogen and C:N ratio by 14%, 8% and 5%, respectively, while obviously decreased values of these parameters were observed under plastic mulching. CONCLUSIONS: Through reducing soil water loss, and improving rainwater use efficiency and soil quality, ridge–furrow grass straw mulching would be a sustainable option for boosting field productivity and thus ensuring local food security in rainfed agricultural areas of Kenya. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Micro-field rain-harvesting farming system (MRFS) has demonstrated great potentials to enhance field productivity and profitability of dryland wheat ( Triticum aestivum L.) in semiarid eastern Asia, yet little is known whether this system results in desired effects in semiarid Africa such as Kenya. A two-year field experiment was conducted during 2012 and 2013 growing seasons to evaluate the effects of introduced MRFS on water availability, field productivity and economic benefits using a local wheat ( T. aestivum L.) cultivar DUMA in a semiarid site of Kenya. Five treatments were designed as: 1) ridge and furrow with transparent plastic mulching (RFT); 2) ridge and furrow with black plastic mulching (RFB); 3) ridge and furrow with grass straw mulching (RFS); 4) ridge and furrow without mulching (RF); and 5) traditional flat planting (CK). The results showed that mulching treatments (RFT, RFB and RFS) significantly decreased the evapotranspiration (ET) by 11.4–88.5 mm, increased wheat grain yield by 60%–163%, above-ground biomass by 58%–104% and water use efficiency for grain by 68%–271%, compared with CK over two growing seasons. RFT and RFB treatments resulted in maximal soil water storage at 1-m depth and the greatest harvest index among all treatments. Linkage analyses indicated that grain yield showed significantly positive correlation with plant height, leaf area and major spike components ( P ≤ 0.05), suggesting that plant type of wheat was altered for better yield production as a result of MRFS operation. More importantly, economic ratios of output to input were also calculated and compared. The average ratio of output to input for CK was 3.86, slightly lower than 4.28, 4.06, 5.86 and 5.34 for RFT, RFB, RFS and RF, respectively across two growing seasons. In particular, net incomes in MRFS (RFT, RFB, RFS and RF) were increased by 145%, 128%, 117% and 82% respectively, compared with that of CK. In conclusion, on-field rain-harvesting farming system provides an innovative management to boost the productivity and profitability of dryland wheat, and a potential solution to cope with food security in semiarid Kenya. [ABSTRACT FROM AUTHOR]

The observed historical changes in crop phenological events are not only as a sensitive indicator to temperature variations but also the consequence of agronomic management such as adjustment of sowing date, cultivar selection and innovative farming practices. Clarifying how these factors influence crop phenology is of paramount importance in understanding/implementing adaptation strategies to future climate change. Changes in phenophases of dryland spring-sown wheat and maize were investigated using the observed phenological data from 1992 to 2013 across the Loess Plateau. Using a series of phenological growth models, we illustrated that once the varietal effect was fixed, rising temperature alone produced a general advancement on dates of heading and maturity, leading to a significant shortening of the vegetative phase (5.2 days decade −1 in wheat and 1.1 days decade −1 in maize), a shortened duration of reproductive phase (0.9 and 2.0 days decade −1 respectively) and the length of whole growing season (6.1 days decade −1 in wheat and 3.0 days decade −1 in maize). In contrast, cultivar shifts prolonged the reproductive duration and the growing season length by 2.2 and 4.7 days decade −1 for spring wheat, and 3.3 and 1.5 days decade −1 for maize, respectively. The continuous update of cultivars during the past two decades has offset 63.5% of the shortening effect of growing season length caused by rising temperature for both crops. Our data indicate that adjusting sowing date and shifts to longer season cultivars are the critical adaptive strategies to cope with temperature increases in dryland spring-sown wheat and maize in the Loess Plateau or regions with similar environments. [ABSTRACT FROM AUTHOR]

We examined three different-ploidy wheat species to elucidate the development of aboveground architecture and its domesticated mechanism under environment-controlled field conditions. Architecture parameters including leaf, stem, spike and canopy morphology were measured together with biomass allocation, leaf net photosynthetic rate and instantaneous water use efficiency (WUEi). Canopy biomass density was decreased from diploid to tetraploid wheat, but increased to maximum in hexaploid wheat. Population yield in hexaploid wheat was higher than in diploid wheat, but the population fitness and individual competition ability was higher in diploid wheats. Plant architecture was modified from a compact type in diploid wheats to an incompact type in tetraploid wheats, and then to a more compact type of hexaploid wheats. Biomass accumulation, population yield, harvest index and the seed to leaf ratio increased from diploid to tetraploid and hexaploid, associated with heavier specific internode weight and greater canopy biomass density in hexaploid and tetraploid than in diploid wheat. Leaf photosynthetic rate and WUEi were decreased from diploid to tetraploid and increased from tetraploid to hexaploid due to more compact leaf type in hexaploid and diploid than in tetraploid. Grain yield formation and WUEi were closely associated with spatial stance of leaves and stems. We conclude that the ideotype of dryland wheats could be based on spatial reconstruction of leaf type and further exertion of leaf photosynthetic rate. [ABSTRACT FROM AUTHOR]

Tracking photosynthesized carbon (C) allocation into different C pools is crucial for management of C sequestration, especially in agroecosystems. However, the effects of long–term tillage management on allocation and dynamics of recently fixed C in the crop–soil–atmosphere system have been rarely investigated under dryland conditions. Using in–situ 13CO 2 repeat labeling, this study quantified the photosynthesized C input to soil, and assessed the responses of allocation dynamics, microbial utilization, and aggregate protection of newly fixed C in three long–term (>10y) tillage practices (no–till, chisel–till, and plow–till) in a dryland wheat cropping system. Regardless of tillage practice, the 13C included into the shoots, roots, soil respiration, rhizosphere, and bulk soils accounted for 46–64%, 4.6–6.0%, 17–38%, 6.4–11.7%, and 2.8–7.2%, respectively, of added 13C over a 35–d chase period. Owing to relatively low plant biomass, compared to plow–till, long–term no–till and chisel–till on average lowered plant 13C fixation and its allocation in rhizosphere soil by 17% and 11%, and 21% and 15%, respectively. Nevertheless, the 13C relocated to bulk soil was significantly higher under both no–till (0.24 g m−2) and chisel–till (0.22 g m−2) than that under plow–till (0.18 g m−2) over the chase period. This could be partially attributed to the decreased allocation of belowground 13C to root–derived CO 2 releases and the increased C retention in both macroaggregates and microaggregates in conservation tillage plots. Moreover, the reduced microbial utilization of new C in rhizosphere soil, as indicated by the low 13C amount in microbial biomass, may further facilitate new C accumulation in bulk soil under reduced tillage. Our findings suggest that despite low photosynthetically–fixed C input to belowground pools during the early growth stages, soils under long–term conservation tillage, in particular no–till, can have a distinct efficiency advantage in soil carbon sequestration by enhancing photosynthesized C preservation in soil aggregates and decreasing new C loss from root–derived CO 2 release in the dryland wheat–soil system. • In–situ 13C labeling was used to assess newly assimilated C allocation in crop–soil system. • Long–term conservation tillage significantly affected C allocation and microbial use in the belowground system. • Both no–till and chisel–till increased C retention in macroaggregates and microaggregates. • Conservation tillage improved new C sequestration efficiency in dryland cropping system. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the mechanisms of assimilate distribution and sugar metabolism in spike-stem that inhibit the formation of fertile florets and grains per spike in winter wheat under pre-reproductive drought stress. Two winter wheat cultivars, CH58 (relatively strongly drought tolerant) and LH6 (relatively weakly drought tolerant), were subjected to successive soil drought treatments from jointing to heading during the 2020–2022 growing seasons. The results showed that pre-reproductive drought stress intensified the degradation and abortion of wheat florets. Compared to CH58, the decrease in the number of fertile florets and grains per spike of LH6 under drought stress increased by an average of 5.3%−8.0% and 8.3%−9.0%, respectively. Drought significantly inhibited the distribution of 13C-photosynthates in wheat spikes (15.7%−24.7%) and stems (8.5%−11.7%) during the booting stage. The number of differentially expressed genes enriched in starch and sucrose metabolic pathways was much higher in the spike and stem of LH6 than in those of CH58. Drought significantly reduced sucrose and hexose in young spikes but increased hexose and fructan concentrations in stems. Compared to LH6, the higher invertase activity and accompanying high expression of sugar transporter protein (STP) in CH58 spikes under drought stress contributed to the utilization of sucrose in young spikes. Additionally, under severe drought, the higher fructan concentration and expression of sugar transport proteins (SWEET and SUT) in the stem of CH58 improved the ability of the stem to transport assimilates to young spikes and thus alleviated the loss of grain number per spike. Exogenous spermidine optimized hexose and sucrose allocation in young wheat spikes and stems after drought stress, thereby increasing the number of fertile florets under drought stress. Overall, the ability of the dominant spike to utilize sugar and the ability to compete for assimilates between the spike and stem contribute to the resistance to drought stress-induced grain reduction in the spike. Exogenous chemicals can regulate the number of fertile florets through this pathway, thereby promoting the formation of wheat grain number. [Display omitted] • Pre-reproduction drought stress exacerbated the decrease in grain number per spike. • The transfer rate of 13C-photosynthate was linearly related to floret degradation. • Drought-resistant wheat had a greater capacity to catabolize sugar in spike. • Dominant stem-to-spike sugar transfer capacity helped floret resist drought. • Exogenous spermidine optimized the allocation of sugar in spike-stem by drought. [ABSTRACT FROM AUTHOR]

The nitrogen application rate and planting density affect soil physiochemical properties, plant physiological characteristics, and soil bacterial community composition. In this study, a two-factor randomized block design was adopted with two planting density levels (high density, HD and low density, LD), and three nitrogen application rate levels (no nitrogen application, N0, low nitrogen application, LN and high nitrogen application, HN). The results showed that the highest yield was produced by LDHN and HDLN, while HDLN had the highest nitrogen use efficiency. Root dry weight was highest in HDHN, followed by HDLN, LDHN and LDLN, while the root nitrogen content was highest in LDHN and HDLN. In the 0–20 cm soil, LDLN had the highest pH and lowest nitrate nitrogen content, HDHN had the lowest pH, and HDLN had the highest content of soluble organic nitrogen and free amino acids. In addition, compared to LDHN, the bacterial community in HDLN and LDLN had higher α diversity and a higher relative abundance of functional genes involved in nitrate reduction. However, HDHN was the opposite. Additionally, correlation analysis also found that the abundance of some bacterial modules was significantly correlated with wheat nitrogen partial factor productivity. Overall, nitrogen application rates and planting density, through changing the physicochemical properties of rhizosphere soil, bacterial composition and function, and wheat root physiological properties, changed the nitrogen utilization and yield of wheat. • Lower nitrogen rate and higher planting density enhanced nitrogen utilization. • Higher nitrogen application rate reduced bacterial community α diversity. • Nitrogen factor explained 41.91 % (p = 0.002) of bacterial composition difference. • Higher planting density and nitrogen rate reduced nitrite reduction genes abundance. • Strong link: certain bacteria module correlates with wheat's nitrogen utilization. [ABSTRACT FROM AUTHOR]

Spatial structural variations in ridge-furrow unit size and its ratio can result in the drastic fluctuation of soil hydrothermal status, and thereby affect water use and yield formation in dryland crops. Previous studies were little focused on the responses of dryland wheat productivity to the structural changes in ridge-furrow plastic mulching (RFM) system and its mechanism in semiarid eastern African Plateau (EAP). A two-year field experiment was conducted in Juja, a semiarid area in Kenya from 2015 to 2016. There were seven treatments of ridge-furrow width and ratios in randomized block design as follows: (1) 40 cm ridge width and 20 cm furrow width (R 4 F 2 , the same below), (2) R 3 F 2 , (3) R 2 F 2 , (4) R 3 F 4 , (5) R 2 F 4 , (6) R 3 F 6 and (7) R 2 F 6 , and conventional flat planting without mulching as control (CK). The results showed that R 4 F 2 , R 3 F 2 , R 2 F 2 , R 3 F 4 and R 2 F 4 treatments significantly improved soil water storage and temperature across two growing seasons compared with CK (P < 0.05). Among all the treatments, R 3 F 2 and R 2 F 2 obviously achieved the highest plant height, leaf area, aboveground biomass (AgB), grain yield and water use efficiency (WUE) (P < 0.05). Also, R 2 F 2 had the highest economic benefits in all treatments. The optimal ridge-furrow ratio appeared to be 1.32–1.38, 1.28–1.31, 1.39–1.49, 1.37–1.45 and 1.46–1.56 for wheat yield, AgB, WUE Y , WUE B and harvest index (HI), respectively. In addition, wheat yield, AgB, WUE and HI tended to decrease linearly with the increased ridge-furrow unit size. In conclusion, ridge-furrow ratio of 1–1.5 (R 2 F 2 to R 3 F 2) in combination with the minimum ridge-furrow unit size proved to be the optimum RFM system for the best dryland wheat productivity in accordance to regional soil and climate characteristics in semiarid EAP and other similar areas of the world. • RFM system significantly increased wheat productivity and WUE in semiarid EAP. • The optimal ridge-furrow ratio was 1.32–1.38 and 1.39–1.49 for yield and WUE. • Wheat yield and WUE decreased linearly with the increasing ridge-furrow unit size. • Ridge-furrow ratio of 1–1.5 combined with a minimum ridge-furrow unit was the optimum RFM system for wheat productivity. [ABSTRACT FROM AUTHOR]