To explore the effect of irrigation at the jointing stage on nitrogen (N) redistribution after flowering and productivity effects of water and N in winter wheat (Triticum aestivum L.), a 2‐yr field experiment was conducted between 2015 and 2017. Three irrigation regimes were designed as follows: rain‐fed (W0), irrigation at jointing and 7 d after flowering (W1), and irrigation at 7 d after flowering (W2). Compared with W2, W1 increased spike number, kernels per spike, and N and dry matter (DM) accumulation at flowering; delayed the senescence of flag leaves after flowering; increased the flag leaf photosynthetic rate, redistribution of N and DM from vegetative organs to grains in the middle and late grain filling stages, and grain yield; and decreased N and DM redistribution and grain weight during early grain development. This may be the reason why the N uptake efficiency and N productive efficiency were higher, whereas the productivities of water and N had no significant difference, and even water productivity was lower under W1 than W2. Therefore, on the basis of suitable water supply from jointing to flowering, achieving a high N and DM accumulation at flowering and high kernels per spike, if the grain development can be accelerated earlier and the redistribution of N and DM can be promoted, it is expected to further improve the productivities of water and N.
To clarify the influence of post-jointing drought on the ear-bearing and seed-setting characteristics of the main stem and tillers of winter wheat (Triticum aestivum L.), a pot experiment was conducted with cultivars "Shannong 29" (SN29) and "Heng 0628" (H0628), and five water regimes: mild drought (WR1) and severe drought (WR2) for 0-5 days after jointing, mild drought (WR3) and severe drought (WR4) for 0-10 days after jointing and adequate water supply as a control (CK). The present study focused on primary tillers (appear in the axils of main stem leaves: T1, T2, T3, T4, etc.), as well as on secondary tillers (appear from the bud in the axil of the prophyll: T10 and T20; appear in the axil of the first leaf of the primary tiller T1: T11). The yield components of tillers showed a downward trend with increasing tiller position and drought degree and duration, and the kernels per spike, single kernels weight and grain yield per spike of tillers T2, T3, T10 and T4 decreased more than those of the other tillers. These outcomes may be related to the spike developmental stages at the time of the drought period. Severe drought during the period from when the stamen primordium is first present (Waddington's stage 4) to when the carpel extends around the three sides of the ovule (Waddington's stage 5) significantly decreased the seed set of tillers, but short-term (5 days) mild drought during this period and even a short-term severe drought before Waddington's stage 4 had little effect on the seed set of tillers. The ear-bearing capacity of tillers was determined not only by the spike developmental stage, but also by the gap from the main stem and the competition of nutrition and space between tillers. Although the ear-bearing rate of tillers T3 and T10 decreased rapidly after the short-term mild drought, the increase in the ear-bearing rate of tillers T20 and T11 effectively compensated for the loss of the number of spikes per plant. Therefore, the short-term mild drought at the jointing stage had no significant effect on the grain yield of the two cultivars. The tillers T2, T3, T10 and T4 were sensitive to soil moisture in the jointing stage and had high plasticity. During this period, if timely irrigation improves soil moisture, it is expected to increase the earbearing rate and seed set of these tillers, thereby increasing grain yield.
To solve the problems of yield reduction and low water-use efficiency (WUE) of winter wheat (Triticum aestivum L.) caused by winter and spring drought, a 2-year field experiment (2017-2019) was performed under movable shelter conditions with the large-and multispike cultivars Shannong 23 and 29, respectively, to explore the optimal supplemental irrigation regime. Three wetting layers were used for irrigation at the jointing stage: 0-10 cm (T2), 0-20 cm (T3) and 0-30 cm (T4). No irrigation at the jointing stage (T1) served as the control. Within a given cultivar, the soil water content in the 0-80 cm soil layers increased after irrigation, and the rate of tiller mortality decreased with increasing depth of the wetting layer used for irrigation at jointing. No significant differences were found between the T3 and T4 treatments in the photosynthetic rate (Pn) of the apical leaf of the main stem (O), the first primary tiller (I) and the fourth tiller (IV) after jointing. However, compared with the T3 treatment, the T4 treatment had a significantly higher transpiration rate (Tr) and lower instantaneous water-use efficiency (WUE leaf ) of the apical leaf of the O and tillers I and IV. This eventually led to a decreasing WUE, although there was no significant change in the spike number or grain yield. These results indicated that moderate irrigation at jointing can effectively reduce the tiller mortality, improve the leaf Pn of the tillers, and increase the spike number and grain yield. However, excessive irrigation can significantly increase the leaf Tr of the tillers, lead to inefficient water consumption and significantly reduce the WUE leaf of the tillers and the WUE. Irrigation at the jointing stage brought the soil water content in the 0-20 cm profile to 100% of field capacity, making it the most suitable supplemental irrigation regime for both the large-and multispike cultivars in the North China Plain.
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