The rice-wheat (RW) cropping system is one of the most prevalent double-cropping systems used to farm the Jianghan Plain in China. However, it can lead to low wheat yields and reduced nitrogen use efficiency compared with dryland wheat (DW). We evaluated wheat yield and nitrogen use efficiency for two rotations (summer rice-winter wheat and summer soybean-winter wheat) from 2017 to 2019 and applied the results to improve nitrogen management for planting wheat after rice in the Jianghan Plain. Field experiments were conducted over two years with two nitrogen treatments: traditional nitrogen management (M1: 90 kg N ha−1 was applied at sowing and jointing, respectively ) and optimized nitrogen management (M2: 60 kg N ha−1 was applied at sowing, wintering and jointing, respectively). The highest total wheat production was achieved under M2 for both cropping systems and the two-year average yield was 6,128 kg ha−1 in DW and 6,166 kg ha−1 in RW. The spike number in DW was 15% higher than RW in M1 and 13% higher in M2, but the kernel per spike and 1,000-grain weight was lower than RW. The nitrogen accumulation of DW was 24% higher than RW in M1 and 33% in M2. Compared with RW, DW had higher NO3− content in the soil surface layer (0–20 cm) and a higher root length density (RLD) in the deeper layer (40–60 cm), which may account for the higher N uptake in DW. Our results show that the grain yield of RW was comparable to that of DW by optimum nitrogen management. The rice-wheat cropping system combined with optimum nitrogen management may be of economic and agronomic benefit to the wheatbelt in the Jianghan Plain in China.

Glasshouse studies with alfalfa (Medicago sativa L.) have shown that improving both forage dry weight (DW) and N concentration (NC) requires selection under N2‐ and NH4NO3‐dependent conditions. The objectives of the present study were to (i) determine genetic variances of forage DW and NC in the field under different levels of N fertilization, (ii) use the genetic variances to predict selection gain for DW and NC at each level of N, (iii) select for increased DW and NC under field conditions and compare actual gains with predicted values, and (iv) compare the efficiencies of field and glasshouse selections for DW and NC. Twenty‐five randomly chosen half‐sib families from ‘Moapa 69’ were planted in each of 2 yr at four locations using a split‐plot design with four levels of N fertilizer (0, 33, 66,100 kg N ha‐1). Forage DW and NC of plants were measured at each location, and individual plants were selected at one location for both DW and NC in each N level using independent culling levels. Genetic variance and predicted gain per cycle for DW were maximized with 100 kg N ha‐1 (118 g kg‐1), while those for NC were greatest without N fertilizer (64 g kg‐1). Selection for either DW or NC alone under these N levels predicted negative correlated responses in the unselected character. Theoretical selection response using independent culling levels for DW followed by NC was greatest under the 33 kg N ha‐1 fertilization level (197 g kg‐1 and 61 g kg‐1 per cycle, respectively). Results of actual selection tests agreed closely with predicted gains and indicate that effective selection for forage DW and NC can be conducted in the field with a low level of N fertilization.

Salt stress negatively affects maize growth and yield. Application of plant growth regulator is an effective way to improve crop salt tolerance, therefore reducing yield loss by salt stress. Here, we used a novel plant growth regulator B2, which is a functional analogue of ABA. With the aim to determine whether B2 alleviates salt stress on maize, we studied its function under hydroponic conditions. When the second leaf was fully developed, it was pretreated with 100 µM ABA, 0.01 µM B2, 0.1 µM B2, and 1 µM B2, independently. After 5 days treatment, NaCl was added into the nutrient solution for salt stress. Our results showed that B2 could enhance salt tolerance in maize, especially when the concentration was 1.0 µMol·L−1. Exogenous application of B2 significantly enhanced root growth, and the root/shoot ratio increased by 7.6% after 6 days treatment under salt stress. Compared with control, the ABA level also decreased by 31% after 6 days, which might have resulted in the root development. What is more, B2 maintained higher photosynthetic capacity in maize leaves under salt stress conditions and increased the activity of antioxidant enzymes and decreased the generation rate of reactive oxygen species by 16.48%. On the other hand, B2 can enhance its water absorption ability by increasing the expression of aquaporin genes ZmPIP1-1 and ZmPIP1-5. In conclusion, the novel plant growth regulator B2 can effectively improve the salt tolerance in maize.

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Yields of wheat crops that succeed rice paddy crops are generally low. To date, it has been unclear whether such low yields were due to rice paddies altering soil physical or mineral characteristics, or both. To investigate this quandary, we conducted field experiments in the Jianghan Plain to analyze differences in the spatial distribution of wheat roots between rice-wheat rotation (RW) and dryland-wheat rotations (DW) using a range of nitrogen treatments. Dryland wheat crops were preceded by either dryland soybean or corn in the prior summer. Biomass of wheat crops in RW systems was significantly lower than that of DW for all N fertilizer treatments, although optimal nitrogen management resulted in comparable wheat yields in both DW and RW. Soil saturated water capacity and non-capillary porosity were higher in DW than RW, whereas soil bulk density was higher in RW. Soil available nitrogen and organic matter were higher in DW than RW irrespective of N application, while soil available P and K were higher under RW both at anthesis and post-harvest stages. At anthesis, root length percentage (RLP) was more concentrated in surface layers (0–20 cm) in RW, whereas at 20–40 cm and 40–60 cm, RLP was higher in DW than RW for all N treatments. At maturity, RLP were ranked 0–20 > 20–40 > 40–60 cm under both cropping systems irrespective of N fertilization. Root length percentage and soil chemical properties at 0–20 cm were positively correlated (r = 0.79 at anthesis, r = 0.68 at post-harvest) with soil available P, while available N (r = −0.59) and soil organic matter (r = −0.39) were negatively correlated with RLP at anthesis. Nitrogen applied at 180 kg ha−1 in three unform amounts of 60 kg N ha−1 at sowing, wintering and jointing resulted in higher yields than other treatments for both cropping systems. Overall, our results suggest that flooding of rice paddies increased bulk density and reduced available nitrogen, inhibiting the growth and yield of subsequent wheat crops relative to rainfed corn or soybean crops.