Jujube tree yields in dryland saline soils are restricted by water shortages and soil salinity. Converting traditional flood irrigation to drip irrigation would solve water deficit and salt stress. The root distribution reacts primarily to the availability of water and nutrients. However, there is little information about the response of jujube roots to the change from flood irrigation to drip irrigation. In this context, a two–year experiment was carried out to reveal the effects of the change from long–term flood irrigation to drip irrigation on soil water, root distribution, fruit yield, and water use efficiency (WUE) of jujube trees. In this study, drip irrigation amounts were designed with three levels, i.e., 880 mm (W1), 660 mm (W2), 440 mm (W3), and the flood irrigation of 1100 mm was designed as the control (CK). The results showed that replacing flood irrigation with drip irrigation significantly altered soil water distribution and increased soil moisture in the topsoil (0–40 cm). In the drip irrigation treatments with high levels, soil water storage in the 0–60 cm soil layer at the flowering and fruit setting, and fruit swelling stages of jujube trees increased significantly compared with the flood irrigation. After two consecutive years of drip irrigation, the treatments with higher irrigation levels increased root length density (RLD) in 0–60 cm soil depth but decreased that in the 60–100 cm depth. In the horizontal direction, higher irrigation levels increased RLD in the distance of 0–50 cm, while reducing RLD in the distance of 50–100 cm. However, the opposite conclusion was obtained in W3 treatment. Additionally, in the second year of drip irrigation, W2 treatment (660 mm) significantly improved yield and WUE, with an increasing of 7.6% for yield and 60.3% for WUE compared to the flood irrigation. In summary, converting flood irrigation to drip irrigation is useful in regulating root distribution and improving WUE, which would be a promising method in jujube cultivation in arid regions.

Accurate nitrogen fertilizer management determines the yield and quality of fruit trees, but there is a lack of multispectral UAV-based nitrogen fertilizer monitoring technology for orchards. Therefore, in this study, a field experiment was conducted by UAV to acquire multispectral images of an apple orchard with dwarf stocks and dense planting in southern Xinjiang and to estimate the nitrogen content of canopy leaves of apple trees by using three machine learning methods. The three inversion methods were partial least squares regression (PLSR), ridge regression (RR), and random forest regression (RFR). The results showed that the RF model could significantly improve the accuracy of estimating the leaf nitrogen content of the apple tree canopy, and the validation set of the four periods of apple trees ranged from 0.670 to 0.797 for R², 0.838 mg L⁻¹ to 4.403 mg L⁻¹ for RMSE, and 1.74 to 2.222 for RPD, among which the RF model of the pre-fruit expansion stage of the 2023 season had the highest accuracy. This paper shows that the apple tree leaf nitrogen content estimation model based on multispectral UAV images constructed by using the RF machine learning method can timely and accurately diagnose the growth condition of apple trees, provide technical support for precise nitrogen fertilizer management in orchards, and provide a certain scientific basis for tree crop growth.

Objective In order to meet the challenge of freshwater resource scarcity and soil salinization in the southern border region，this study investigates the effects of brackish water drip irrigation on the distribution of substrate water and salt，growth and yield of facility tomato under the yellow sand cultivation mode.Moreover，the study explores the dynamic growth change of tomato by using the Logistic model to determine the threshold of mineralization for brackish water drip irrigation of facility tomato under the yellow sand cultivation mode in the southern border region，thus providing the theoretical basis and technological support for the efficient use of brackish water in facility agriculture in the region. Method In this experiment，five irrigation water mineralization treatments of 2 g/L（T₁），3 g/L（T₂），4 g/L（T₃），5 g/L（T₄）and 6 g/L（T₅）were set up with yellow sand substrate facility tomato as the research object，and freshwater irrigation as the control（CK）was used to investigate the effect of brackish drip irrigation on the distribution of substrate water salinity，the growth and development of the facility tomato，the constituent factors of yield，and the efficiency of irrigation water use under the yellow sand cultivation mode. Result Under the yellow sand cultivation mode，the water content and salinity of the substrate of each treatment during the whole reproductive period were positively correlated with the mineralization of irrigation water，and both increased with the increase of the mineralization of irrigation water；the average water content of the substrate of each treatment from 0 to 25 cm in different reproductive periods of tomato reached the maximum in the flowering and fruiting period，of which the increase of the average water content of the substrate of 2 g/L was not obvious when compared with that of the CK treatment.The average water content of the substrate of 2 g/L significantly increased when the mineralization increased to 3 g/L or more.Compared with the CK treatment，the increase in the average water content of 2 g/L substrate was not obvious.When the mineralization increased to more than 3 g/L，the average water content of substrate was significantly higher，increased by 7.51%，10.67%，14.44% and 18.10%，respectively；the average salinity of 0-25 cm substrate at different fertility periods of tomato reached a peak at the end of fruiting，of which the salt accumulation effect of T₃，T₄ and T₅ treatments was more obvious，and the salt content of the substrate was as high as 8.49，9.82 and 10.50 g/kg.Tomato plant height，stem thickness and dry matter growth showed an S-shaped trend of gradual increase and then basically unchanged with the advancement of fertility.The logistic model could be used to accurately describe the dynamic growth process of tomato plant height，stem thickness and dry matter accumulation under different treatments of irrigation water mineralization.The determination coefficient R² of the fitting equation was above 0.94.The growth indexes，total yield and irrigation water use efficiency of tomato showed a trend of increasing and then decreasing with the increase of irrigation water mineralization，in which the total yield and irrigation water use efficiency of 3 g/L reached 47.17 t/hm² and 15.22 kg/m³，respectively，which were significantly higher than those of the other treatments. Conclusion Considering the growth and development of tomato and yield and other factors，this study recommends 2-3 g/L irrigation water mineralization for facility tomato under yellow sand cultivation mode，which can effectively alleviate the shortage of fresh water and soil salinity.This study provides scientific basis for the large-scale popularization of sand cultivation of tomato in the southern border area.