Water shortages due to low precipitation and seawater intrusion in the Lower China Yellow River Delta have occurred in recent years. Exploiting underground brackish water through well drilling is a potential alternative way to satisfy the demand for agricultural irrigation. However, how to successfully use brackish water for irrigation has become a new problem to solve. A two-year field experiment was conducted in this typical saline-alkaline region to investigate the effects of irrigating with brackish water on the soil water-salt dynamics, and the physiological response of winter wheat to drought-salt stress. The experiment was laid out in a randomized block design with three replications according to the quantity (160 mm and 240 mm) and quality (fresh water and brackish water with a salt concentration of 3 g L⁻¹) of irrigation water: T1 was 240 mm of fresh water, T2 was 160 mm of fresh water, T3 was 80 mm of fresh water and 160 mm of brackish water, and T4 was 80 mm of fresh water and 80 mm of brackish water. The results showed that the soil moisture of T3 was almost the same as T1 after the harvest of winter wheat each year, therefore, irrigating with brackish water can maintain soil moisture while saving fresh water resources. After two years, the soil salinity of each treatment increased by 0.307, 0.406, 0.383, and 0.889 g kg⁻¹, respectively. During the jointing-flowering stage, salt stress has a significant inhibitory effect on photosynthesis; T3 and T4 were lower than T1 and T2 in terms of plant height and dry weight. During the filling stage, because the effect of drought stress is more serious than that of salt stress, the photosynthesis of T3 was greater than that of T2 and T4. For both years, the yield of crops followed the rank order T1 > T3 > T2 > T4. Compared with irrigating with fresh water in T1, T3 changed the second and third irrigation into brackish water, however we did not find that soil salinity increased significantly, and this treatment was able to ensure crop growth during the filling stage. Therefore, the combination of fresh water (80 mm), then brackish water (80 mm), then brackish water (80 mm) is a feasible irrigation strategy in China’s Yellow River Delta for winter wheat.

One of the primary factors in the hydrological cycle is reference evapotranspiration (ET₀). The prediction of ET₀ is crucial to manage irrigation water in agriculture under climate change; however, little research has been conducted on the trends of ET₀ changes in Shandong Province. In this study, to estimate ET₀ in the entire Shandong Province, 245 sites were chosen, and the monthly ET₀ values during 1901–2020 were computed using the Hargreaves–Samani formula. A deep learning model, termed SAO-CNN-BiGRU-Attention, was utilized to forecast the monthly ET₀ during 2021–2100, and the predictions were compared to two CMIP6 climate scenarios, SSP2-4.5 and SSP5-8.5. The hierarchical clustering results revealed that Shandong Province encompassed three homogeneous regions. The ET₀ values of Clusters H1 and H2, which were situated in inland regions and major agricultural areas, were the highest. The SAO-CNN-BiGRU-Attention and SSP5-8.5 forecasting results generally displayed a monotonically growing trend during the forecast period in the three regions; however, the SAO-CNN-BiGRU-Attention model displayed a declining tendency at a few points. According to the SAO-CNN-BiGRU-Attention and SSP5-8.5 results, during 2091–2100, H1, H2, and H3 will reach their peaks; the SSP2-4.5 results show that H1, H2, and H3 will peak in 2031–2040. At the end of the forecast period, for Clusters H1, H2, and H3, the prediction rate of SAO-CNN-BiGRU-Attention increased by 1.31, 1.56%, and 1.80%, respectively, whereas SSP2-4.5’s prediction rate increased by 0.31%, 0.95%, and 1.57%, respectively, and SSP5-8.5’s prediction rate increased by 10.88%, 10.76%, and 10.69%, respectively. The prediction results of SAO-CNN-BiGRU-Attention were similar to those of SSP2-4.5 (R² > 0.96). The SAO-CNN-BiGRU-Attention deep learning model can be used to forecast future ET₀.

The experiment of winter wheat brackish water irrigation was carried out in Xiawa Town, Zhanhua District, Shandong Province from 2015 to 2016. Four different irrigation schemes were designed by using fresh water and brackish water of salinity of 3.0g/L. The effect of brackish water irrigation on the distribution of water-salt in saline alkali soil was studied. The results showed that the soil water content of three times irrigation could reach 12.5% ~ 19.9%, while that of twice irrigation could only reach 10.8% ~ 13.6% and the salt accumulation of the scheme of fresh water + fresh water + brackish water was 0.0552g/kg, which indicated that this scheme could not only supplement soil water but also accumulate less salt.

Biochar has been extensively used for the improvement of soil environment in fields. However, the effects of biochar on soil water movement and crop productivity under different irrigation rates were not well clear or consistent. The objectives of this study were to investigate whether biochar could prevent the production of preferential soil flow, and to study the effects of biochar and irrigation on soil properties, nutrient leaching, crop growth and yield, which was of great significance to improve crop water and fertilizer use efficiency and protect the ecological environment. The experiments included two parts, i) short-term blue dye tracer test, to investigate the effect of biochar application (20 and 40 t/hm2) on the degree of preferential flow, and ii) a field trial with winter wheat (Triticum aestivum L.) as test material was conducted in the lysimeters in 2018-2019, to investigate the effect of biochar application (20 t/hm2) on the soil nitrate nitrogen distribution and wheat yield under two irrigation rates (0.6 reference crop water requirement (ETc), 0.8 ETc). The results showed that i) within the designed biochar application rates, the degree of preferential flow was decreased with the increase of biochar application, but the decreasing speed slowed down significantly, with the preferential flow fraction (PF-fr) reduced by 6%~17.5%, especially under high irrigation, ii) compared with the control treatment, biochar improved the capacity of the soils to retain nutrients, alleviated the negative effect of water shortage, and increased winter wheat productivity. Our results suggested that the 0.8 ETc irrigation and 20 t/hm2 biochar was recommended in the field condition.

In order to explore the water and fertilizer utilization of summer corn and optimize a management scheme of water and fertilizer for summer corn in North China Plain. Plot experiments of summer corn were conducted at Shandong Irrigation Experiment Center Station in Jinan. This paper analyzed the characteristics of nitrogen (N) and phosphorus (P) content in soil and partial factor productivity. The NO₃₋-N was the main form of residual N in soil, while P mainly distributed differently in the upper layer. N and P migrated downward more quickly under high irrigation, and the migration speed of N was faster than that of P. When the application of P and N were respectively 90 kg/hm² and 192 kg/hm², the NPFP and the PPFP were respectively the highest. Based on the above research results, it can be suggested that the management with 121.5 mm irrigation, 192 kg/hm² nitrogen and 90 kg/hm² phosphorus was the better cultivation practice for summer corn.