A field experiment was conducted to evaluate the effects of regulated deficit irrigation (RDI) on the fine root redistribution of mature pear trees in 2009 and 2010. The experiment consisted of four RDI treatments: MRDI-1 and SRDI-1, in which the trees received irrigation replacing 60% and 40% of pan evaporation (Ep) during Stage 1 (cell division stage), and MRDI-1+2 and SRDI-1+2, in which the trees received irrigation replacing 60% and 40% of Ep during Stage 1+2 (cell division and slow shoot growth stage). All the RDI-treated trees received irrigation replacing 80% of Ep (full irrigation) in other stages, and the control trees were fully irrigated during the whole growth season. The results showed that the fine root length density (RLD) of mature pear trees was reduced by water stress. The resumption of full irrigation boosted fine root growth. The RLD of the SRDI-1-treated trees in the irrigated zones recovered in early July, they maintained water and nutrient absorption during the fruit enlargement stage, and the final fruit yield was significantly improved. The RLD of trees in the irrigated zones with MRDI-1 and MRDI-1+2 recovered in July and September, respectively, but there were no significant differences in fruit yield between the MRDI-1, MRDI-1+2, and the control. This indicates that the fruit yield was not negatively or positively impacted by the redistribution of moderate water stress applied during either Stage 1 or Stage 1+2.

Nitrogen is one of the essential elements for fruit tree growth. Therefore, a ¹⁵N tracing experiment was conducted to investigate the characteristics of nitrogen uptake and distribution in young pear trees. The experiment included: groups A and B, fertilized with 15 g unlabeled and 5 g labeled N per tree in the spring of 2017; and group C, fertilized with 20 g unlabeled N per tree in the spring of 2017 and 25 g unlabeled and 5 g labeled N per tree in the spring of 2018. Results indicated that new organs grew vigorously before June, and about 50% of the fertilizer nitrogen was concentrated in leaves. From June to November, the growth rate of storage organs was faster than that of new organs, and fertilizer nitrogen was mainly stored in the shoots, trunk, and roots. During the defoliation period, about 84% of the leaf fertilizer nitrogen was mobilized to the shoots, trunk, and roots. There was significant correlation between current fertilizer nitrogen and the dry mass weight of each organ after the completion of the nitrogen cycling of a whole year; the correlation coefficient was 0.98. Fertilizer nitrogen use efficiency increased with the ages of the pear trees. Therefore, nitrogen fertilizer rate should be formulated according to the tree growth characteristics and increased with the ages of the young pear trees; topdressing fertilizer should be applied in summer to ensure trunk and root development.

A field experiment was conducted in 2023 and 2024 in Beijing, China, to investigate effects of soil water stress, applied before the fruit ripening stage, on the fruit total soluble solid accumulation and cracking of jujube trees. The experiment consisted of two variation factors: (a) irrigation levels (MDI and SDI, applied 80% and 50% of the irrigation volume, respectively) and (b) growth stages (stage 1, before the fruit enlargement stage, and 2, before the fruit ripening stage). The two irrigation levels were applied at each growth stage in a 2 × 2 factorial arrangement, plus a control treatment receiving 100% irrigation volume, resulting in five treatments per replicate. The findings indicated that pre-enlargement stage water stress enhanced the accumulation of total soluble solid content within fruits, which subsequently promoted faster fruit growth in from the early- to mid-August period. However, by late August, both the total soluble solid content and fruit growth rates had declined, thereby mitigating the risk of fruit cracking. During the fruit enlargement stage, the fruit total soluble solid content in SDI-2 increased by approximately 24% by the end of August compared to the control, leading to lower osmotic potential and higher turgor pressure during the following ripening stage. As skin growth ceased, high turgor pressure caused fruit cracking at the following ripening stage. The SDI-2 treatment demonstrated a fruit cracking rate approximately 1.5 times higher than that of the control. Pearson correlation analysis also indicated that fruit cracking was positively correlated with total soluble solids accumulated in August. Meanwhile, the yield of SDI-2 was reduced about 18%. Therefore, the adequate soil moisture during the fruit enlargement stage was crucial to minimize jujube fruit cracking and economic losses. Meanwhile, the deficit irrigation applied during the pre-enlargement stage could effectively conserve water resources and mitigate the occurrence of extensive jujube fruit cracking.

Polyacrylamide (PAM), as a widely used effective soil conditioner, can decrease sandy soil infiltration, but its function may decline significantly in a short time. Previous study results showed that the annual degradation rate of PAM in soil is about 10%, and the migration ability of PAM in soil is fairly weak; thus we hypothesized that the functional group of PAM is prone to aging caused by physical and biological factors, which is different from degradation caused by the breaking of long main chains into short ones. The sandy loam soil was selected to conduct column infiltration experiments to (1) determine the effects of PAM application and drying and wetting intensity on infiltration and (2) identify the causes of the aging effect. Soil samples were treated with three doses of PAM (0, 1, and 2 g·kg⁻¹) and incubated in three soil water conditions (constant wetting, moderate and strong drying/wetting cycles). Under constant wetting condition, the stable infiltration rates of soils were decreased by PAM. However, after two strong drying and wetting cycles, the decrement of infiltration rates of PAM-treated soils was reversed. The results of FTIR suggested that drying and wetting cycles led to the hydrolysis of amide groups in PAM, resulting in the weakening of PAM’s function on soil infiltration characteristics. The leaching amounts of NH₄⁺-N generated by the amide group hydrolysis increased through the drying/wetting alternation and the application of PAM. Therefore, based on the findings of this column study using a specific sandy loam soil under controlled intense drying–wetting cycles, reapplication of polyacrylamide (PAM) after two cycles may facilitate the sustained lowering of infiltration. However, this recommendation should be confined to analogous experimental conditions and necessitates further validation under field scenarios or for alternative soil types.

Soil water flux is a key parameter for understanding water and heat transport processes in the vadose zone. The heat pulse technique (HPT) has shown considerable potential for predicting soil water flux. Traditional three-needle probe methods, the maximum dimensionless temperature difference (MDTD) method and the ratio of downstream to upstream temperature increases (Ratio) method, can only measure water flux along the probe alignment. To enhance the applicability of the HPT method, the five-needle probe with vector addition allows for the measurement of soil water flux in any direction within the plane perpendicular to the needles. However, its applicability across different soil textures remains unclear. The objective of this study was to evaluate the applicability of the MDTD and Ratio methods when combined with vector addition across different soil textures. Experimental results show that the vector MDTD and Ratio methods improve water flux measurement accuracy compared with traditional three-needle methods, confirming the reliability of the vector HPT approach. Specifically, the mean absolute percentage error (MAPE) of the vector MDTD method decreased by 1.69%, 1.04%, and 1.80% in sand, sandy loam, and silt loam, respectively, compared with the traditional MDTD method. In contrast, the MAPE of the vector Ratio method varied by +8.83%, −6.73%, and −18.20% in the same soils, relative to the traditional Ratio method. Examining the root mean square error (RMSE) of each method yields a similar conclusion. Similarly to traditional HPT methods, the measurement accuracy of the vector HPT approach is influenced by soil texture, water flux range, and probe spacing. Notably, because the vector HPT method involves four probe spacings, namely the distances between the heating needle and the temperature-sensing needles, it can exacerbate the instability of the resultant water flux measurements. These findings may facilitate the broader application of the HPT method.