The technology for reducing cadmium (Cd) contamination in rice is being explored globally. In this study, the ratios of nitrogen fertilizers used were 5:5:0:0 (T1), 4:4:2:0 (T2), 6:0:2:2 (T3), and 3:2:2:3 (T4). The objective of the pot experiment was to understand how nitrogen management can reduce Cd accumulation in rice by influencing soil pH, the bioavailability of Cd concentrations in soil, Cd adsorption by iron membranes on rice roots, and the transport of mineral elements. The results indicated that nitrogen fertilizer application acidifies the soil and increases the bioavailable Cd concentration. A correlation analysis revealed a significant positive correlation between Cd concentration in the Fe plaque on rice roots and Cd concentration in the roots. Overall, the application of nitrogen fertilizers increased the concentrations of Cd and mineral elements in rice tissues, particularly in Cu, Mn, and Zn, but reduced the transfer of Cd between tissues. After nitrogen application, the concentrations of mineral elements in brown rice significantly increased, with negative correlations being observed between the Cu, Mn, and Zn concentrations and Cd concentration in brown rice. The brown rice with a nitrogen fertilizer proportion of 6:0:2:2 exhibited the lowest Cd concentration, showing significant reductions of 48.04% (X13H) and 43.46% (YZX) compared to the control treatment. These findings suggest that nitrogen management can enhance the coefficients of mineral element uptake in rice, compete against the transport of Cd to the grains, and that late-growth-stage nitrogen application can be more effective in reducing Cd concentration in brown rice.

Mechanical transplanting often causes root damage to rice seedlings, but its yield impacts in double-cropping systems remain unclear. A two-year field experiment was conducted in early- and late-season rice under three root damage treatments: no damage (CK), mild root damage (T1, seedling roots pruned to 2 cm), and severe root damage (T2, seedling roots pruned to 1 cm). Results showed that T2 reduced early-season rice yield by 8% but had no significant effect on late-season rice, while T1 did not affect yield in either season. In early-season rice, the yield loss was associated with reduced pre-heading biomass (BM_Pre) and total biomass (both 13% lower than CK), primarily due to decreases of 5–32% in SPAD, leaf area index, specific leaf weight, pre-heading crop growth rate, and leaf area duration, with no post-heading compensation. In contrast, late-season rice sustained yield despite a 9% reduction in BM_Pre (attributed to similar leaf trait reductions of 4–26%) by enhancing post-heading biomass (16% increase), driven by a 17% increase in post-heading crop growth rate and an 11% decrease in the rate of leaf area decline. Partial least squares path modeling confirmed that biomass dynamics, rather than yield components, constituted the primary pathway linking root damage to yield. These results demonstrate that the impact of root damage is season-dependent, highlighting the need for root protection in early-season rice and the exploitation of compensatory capacity in late-season rice to optimize mechanical transplanting practices.

Yield loss from mechanical transplanting in early-season rice is often attributed to root damage, yet the physiological mechanism remains poorly understood. A two-year field experiment was conducted in early-season rice with two varieties (Lingliangyou 211, hybrid; Zhongzao 39, conventional inbred) under three root damage treatments: no damage (CK), mild (roots trimmed to 2 cm, T1), and severe (roots trimmed to 1 cm, T2). Root regeneration, leaf water status, antioxidant enzyme activities (SOD, POD, CAT), malondialdehyde (MDA), soluble protein, and PSII maximum quantum yield (Fv/Fm) were measured at 1, 3, 5, and 7 days after transplanting in 2022, whereas grain yield and yield components were evaluated in both 2021 and 2022. Results showed that T2 reduced grain yield by 8–9% across both years, whereas T1 had no significant effect. The two varieties exhibited consistent physiological responses to root damage. Both T1 and T2 stimulated compensatory new root proliferation, with significantly higher new root numbers at days 5–7 relative to CK. However, T2 induced sustained oxidative stress, as indicated by elevated MDA in roots throughout the recovery period and in leaves from day 5 onward. In contrast, T1 caused only a transient increase in root MDA. T2 reduced Fv/Fm by 23–26%, pre-heading biomass production by 13%, and highest tiller number by 10–21%. Conversely, T1 maintained all these parameters at control levels. Severe root damage reduced PSII photochemical efficiency and biomass in association with systemic oxidative stress, whereas mild damage was effectively contained. These findings indicate that, under the tested conditions, severe root trimming that leaves approximately 1 cm of intact roots was detrimental to grain yield, whereas retaining approximately 2 cm did not significantly compromise productivity.

Soil cadmium (Cd) contamination has become a serious problem in China. In this study, the goals of the field experiments were to understand how the application of nitrogen fertilizer at the full heading stage and filling stage reduced the uptake of Cd in rice by affecting the distribution of Cd in iron plaques on the root surfaces and subcellular in the root and flag leaf. The hydroponic culture experiments aimed to explore the effect of interaction or deficiency of nitrogen and cadmium on cadmium accumulation in rice at the late growth stage. The results showed that under the condition of having enough nitrogen supply during the early growth stage, applying nitrogen fertilizer during the full heading stage and filling stage resulted in a significant increase in the concentration of Fe and Cd on the root plaques at the milk stage and mature stage. Additionally, it increased the concentration and proportion of Cd in the soluble fraction of subcellular in the flag leaves at the milk stage. On the other hand, when there was a deficiency of nitrogen, the concentration of Fe in the root plaques increased significantly, while the concentration of Cd in the root plaques decreased significantly. Moreover, the proportion of Cd in the flag leaf cell walls increased significantly. Regardless of whether there was sufficient or deficient nitrogen supply during the early growth stage, applying nitrogen at the full heading stage reduced the Cd concentration in brown rice by 35.11% and 57.25%, respectively. Under hydroponic culture conditions with both Cd exposure and later-stage nitrogen supply significantly increased the Cd concentration in brown rice. However, in the absence of Cd, nitrogen supply significantly reduced the Cd concentration in brown rice. The accumulation of Cd in brown rice was significantly correlated with the accumulation of Fe and Mn at the late growth stage. Our findings indicate that when there is sufficient nitrogen nutrition during the early growth stage of rice, topdressing nitrogen fertilizer at the full heading stage combined with lime with mineral element fertilizers such as Fe and Mn is an effective approach to reduce the presence of cadmium in rice grains.