The objective of this paper is to perform drip irrigation scheduling for spinach (Spinacia oleracea L.) in a plastic greenhouse using the standard 20 cm evaporation pan. A drip irrigation experiment with four levels of irrigation, i.e., 0.6, 0.8, 1.0, and 1.2 times the cumulative evaporation of a 20 cm standard pan (Epan) were set up. The irrigation interval was controlled using a 20 mm Epan, and optimal irrigation water amounts of 0.8 Epan and 0.6 Epan were recommended for the spring and autumn growing seasons, respectively. Overirrigation (1.2 Epan) also led to yield losses, particularly for stem growth. In addition, a proper greenhouse index, defined as the ratio of the cumulative Epan inside and outside the greenhouse, could predict the Epan inside the greenhouse using the external Epan to a high degree of accuracy (daily data with r² = 0.85, root mean square error (RMSE = 0.68 mm d⁻¹), for a 4-day interval with r² = 0.95, RMSE = 1.81 mm 4 day⁻¹, and for the entire growth period with r² = 1.0, RMSE = 2.40 mm). A simple and low-cost greenhouse index method could be used to formulate drip irrigation schedules for spinach in low-technology plastic greenhouses using a 20 cm standard pan outside the greenhouse.

Organic amendment is an effective method to reclaim salt-affected soil. However, in coastal land with shallow saline groundwater, it is limited known about the mechanism of organic amendment on soil desalinization. Thus, to examine the effect of topsoil organic matter content on soil water/salt transport and distribution, two-year field observations in Bohai coastal land, North China, and soil column experiments simulating salt accumulation and salt leaching were conducted, respectively. There were different organic fertilizer amendment rates in 0–20 cm topsoil, 0% (CK), 50% (OA 0.5), and 100% (OA 1.0) (w/w) for soil column experiments. Field observation showed that after organic amendment (OA), the soil’s physical structure was improved, and less of the increase in topsoil salt content was observed, with more salt accumulated in deep soil layers during the dry season. In addition, OA greatly promoted salt leaching during the rainy seasons. The results of the soil column tests further indicated that OA treatments significantly inhibited soil evaporation, with less salt accumulated in the topsoil. Although there was no difference in soil water distribution between the CK and OA 0.5 treatment, the topsoil EC for the OA 0.5 treatment was significantly lower than that for CK. During soil water infiltration, the OA 0.5 and OA 1.0 treatments significantly increased the infiltration rates, enhanced the wetting front, and promoted salt leaching to deeper soil layers, compared with CK. The improvement of soil organic amounts could make the soil more self-resistant to the coastal salinization. The findings of this study provide some insights into soil water/salt regulation in heterogeneous soil masses and on the permanent management of coastal saline farmland.

Accurate estimation of crop evapotranspiration (ET_c) is important to determine crop water requirements in greenhouse agriculture and to improve the irrigation water use efficiency. Here, a 3-year (2017–2019) experiment with spring greenhouse-grown eggplant (Solanum melongena L.) was conducted to investigate variation in the crop coefficient (K_c) measured with a weighing lysimeter, adjust K_c based on the local climate (K_c,Adj), and estimate daily ET_c using a crop coefficient model. The 3-years mean local K_c (K_c,Loc) were 0.23 ± 0.03, 0.62 ± 0.06, 1.05 ± 0.03 and 0.87 ± 0.03 at the initial, development, mid-season, and end-season stages, respectively. Significant linear correlation was observed between K_c,Adj and K_c,Loc in the 3 years (R² = 0.873, 0.901, and 0.897 in 2017–2019, respectively). Compared with the FAO-56 recommended K_c value (K_c,FAO), the mean K_c,Adj and K_c,Loc in the 3 years were by 66.3% and 61.8% lower, respectively. The single crop coefficient model accurately estimated daily ET_c for greenhouse-grown eggplant. The coefficient of determination (R²), mean absolute error (MAE), root-mean-squared error (RMSE), and index of agreement between measured ET_c and that estimated by the single crop coefficient model were 0.94, 0.35 mm‧d⁻¹, 0.26 mm‧d⁻¹, and 0.98, respectively, for the means in 2018 and 2019. Therefore, the crop coefficient method reliably estimated evapotranspiration with adjustment for the actual environment and can serve as a useful tool to improve water use efficiency.

To scientifically evaluate the effects of three environmentally friendly fumigants, dazomet, metham sodium, and calcium cyanamide, on soil microbial community changes, soil from a greenhouse with 7 years of continuous cropping was studied. Soil samples were collected from unfumigated soil (CK), dazomet-fumigated soil (DZ1), metham sodium-fumigated soil (MS1), calcium cyanamide-fumigated soil (CC1) at seedling recovery stage, dazomet-fumigated soil (DZ2), metham sodium-fumigated soil (MS2), and calcium cyanamide-fumigated soil (CC2) at fruiting stage. The effects of different fumigant treatments and treatment periods on soil microbial community changes, tomato yield, and soil-borne diseases were analyzed. The results showed that the application of soil fumigants significantly reduced the richness and diversity of soil bacterial and fungal communities at the seedling recovery stage. Three months after transplanting (at the fruiting stage), the soil microbial diversity gradually recovered. After fumigation, the relative abundance of soil bacteria and fungi at the phylum level changed. Under different fumigation treatments, the trends in the relative abundance changes of species during the seedling recovery and fruiting stages after fumigation exhibited certain differences. Analysis of the dominant soil microbial communities at the genus level revealed that fumigation effectively eliminated pathogenic genera such as Fusarium, but the inhibition rate of pathogens increased during the seedling recovery stage after fumigation. By comprehensively considering microbial community changes during the seedling recovery and fruiting stages after fumigation, as well as indicators such as yield, incidence of soil-borne diseases, and disease index, among the three fumigation treatments, the DZ treatment demonstrated the best overall performance. It increased beneficial genera while reducing the majority of pathogenic genera in the soil. Even after three months, when the plants transitioned from the seedling recovery stage to the fruiting stage, the relative abundance of harmful genera remained suppressed, and the abundance of some beneficial genera increased. However, given the broad-spectrum microbial eradication by fumigants and the time-limited suppression of pathogenic communities, it is essential to supplement beneficial microorganisms promptly after soil fumigation, such as by applying microbial fertilizers in combination.

To scientifically assess the effects of environmentally friendly fumigants on soil microbial communities, soils from a 7-year continuous cropping tomato greenhouse were studied, with unfumigated soil used as the control (CK). Rhizosphere soil samples treated with dazomet (DZ), metam sodium (MS) and calcium cyanamide (CC) were collected at the seedling recovery and fruiting stages. The influences of different fumigants and growth stages on soil microbial communities, tomato yield and soil-borne diseases were investigated. The results indicated that soil fumigation significantly decreased microbial community richness and diversity at the seedling recovery stage, which gradually recovered at the fruiting stage. The variation trends of microbial relative abundance at the phylum and genus levels differed among the treatments at both stages. At the phylum level, Actinobacteria and Proteobacteria were the dominant bacterial phyla, and Ascomycota was the dominant fungal phylum. Genus-level clustering revealed that the bacterial communities under MS and CC were similar to those under CK at the fruiting stage, whereas the fungal communities under all the fumigation treatments were significantly distinct from those under CK. Fumigation effectively inhibited pathogenic genera, including Amesia, Fusarium, Rhizopus and Ascobolus, at the seedling recovery stage, but some pathogens recovered at the fruiting stage. The relative abundance of Fusarium in the MS treatment increased to 8.25%. DZ treatment performed optimally: it increased beneficial genera such as Bacillus and Streptomyces at the seedling recovery stage, suppressed harmful genera, including Amesia and Fusarium, and further enriched Remersonia at the fruiting stage. Fumigation significantly improved tomato yield and reduced the incidence of soil-borne diseases. The yield of CC was the highest, at 35.41% greater than that of CK, but it was not significantly different from that of DZ in terms of cost. In conclusion, the DZ treatment had the best overall effect.

To explore the effects of different irrigation approaches, mulching, and their interaction on greenhouse melon (Cucumis melo L.) production and water use, a field experiment was conducted in Northern China using four treatments: mulching drip irrigation (MDI), mulching furrow irrigation (MFI), drip irrigation (DI), and furrow irrigation (FI; CK). The plant biomass, yield, water consumption, and water use efficiency (WUE) of melons were measured at different growth stages. The results showed that mulching has significant positive impacts on the growth as well as the fruit yield of melons. However, the water use characteristics of the plant were more greatly determined by the various irrigation approaches, and there was a significant interaction between the irrigation approach and mulching for both the total water consumption and WUE of the greenhouse melon. Of these treatments, MDI resulted in the highest yield of 38.49 t/hm², which was significantly higher than the yields obtained with DI (32.36 t·hm⁻²) and FI (CK, 30.34 t·hm⁻²). In addition, the water consumption under MDI was 45.80% lower than FI (CK), which resulted in the promotion of WUE under MDI. The WUE range of the greenhouse melon is as follows: MDI (334.77 kg·mm⁻¹·hm⁻²) > DI (244.84 kg·mm⁻¹·hm⁻²) > MFI (189.78 kg·mm⁻¹·hm⁻²) > FI (CK; 142.94 kg·mm⁻¹·hm⁻²). The findings of this study indicate that mulching can boost melon yield, and drip irrigation can limit water consumption. This study provides a reference point for policymakers, indicating that drip irrigation with plastic mulching could be a feasible adaptation strategy for increasing greenhouse melon production in Northern China, as well as other agriculture regions that suffer from water shortages.