A hybrid CNN-LSTM model for diagnosing rice nutrient levels at the rice panicle initiation stage

Nitrogen(N)and potassium(K)are two key mineral nutrient elements involved in rice growth.Accurate diagnosis of N and K status is very important for the rational application of fertilizers at a specific rice growth stage.Therefore,we propose a hybrid model for diagnosing rice nutrient levels at the early panicle initiation stage(EPIS),which combines a convolutional neural network(CNN)with an attention mechanism and a long short-term memory network(LSTM).The model was validated on a large set of sequential images collected by an unmanned aerial vehicle(UAV)from rice canopies at different growth stages during a two-year experiment.Compared with VGG16,AlexNet,GoogleNet,DenseNet,and inceptionV3,ResNet101 combined with LSTM obtained the highest average accuracy of 83.81%on the dataset of Huanghuazhan(HHZ,an indica cultivar).When tested on the datasets of HHZ and Xiushui 134(XS134,a japonica rice variety)in 2021,the ResNet101-LSTM model enhanced with the squeeze-and-excitation(SE)block achieved the highest accuracies of 85.38 and 88.38%,respectively.Through the cross-dataset method,the average accuracies on the HHZ and XS134 datasets tested in 2022 were 81.25 and 82.50%,respectively,showing a good generalization.Our proposed model works with the dynamic information of different rice growth stages and can efficiently diagnose different rice nutrient status levels at EPIS,which are helpful for making practical decisions regarding rational fertilization treatments at the panicle initiation stage.

Effect of various crop rotations on rice yield and nitrogen use efficiency in paddy–upland systems in southeastern China

To evaluate the effects of various rotation systems on rice grain yield and N use efficiency, a paddy–upland cropping experiment(2013–2016) was conducted in southeastern China. The experiment was designed using six different rice––winter crop rotations: rice–fallow(RF),rice–wheat(RW), rice–potato with rice straw mulch(RP), rice–green manure(Chinese milk vetch; RC–G), rice–oilseed rape(RO), and rice–green manure crop(oilseed rape with fresh straw incorporated into soil at flowering; RO–G) and three N rates, N0(0 kg N ha-1), N1(142.5 kg N ha-1), and N2(202.5 kg N ha-1). Average rice yields in the RF(5.93 t ha-1) rotation were significantly lower than those in the rotations with winter crops(7.20–7.48 t ha-1)under the N0 treatment, suggesting that incorporation of straw might be more effective for increasing soil N than winter fallow. The rice yield differences among the rotations varied by year with the N input. In general, the grain yields in the RP and RO–G rotations –were respectively 11.6–28.5% and 14.80–37.19% higher than those in the RF in plots with N applied. Increasing the N rate may have tended to minimize the average yield gap between the RF and the other rotations; the yield gaps were 18.55%, 4.14%, and 0.23% in N0, N1, and N2, respectively. However, the N recovery efficiency in the RF was significantly lower than that in other rotations, except for 2015 under both N1 and N2 rates, a finding that implies a large amount of chemical N loss. No significant differences in nitrogen agronomic efficiency(NAE) and physiological efficiency(NPE) were found between the rotations with legume(RC–G) and non–legume(RO and RW) winter crops, a result that may be due partly to straw incorporation. For this reason, we concluded that the return of straw could reduce differences in N use efficiency between rotations with and without legume crops. The degree of synchrony between the crop N demand and the N supply was evaluated by comparison of nitrogen balance degree(NBD) values. The NBD values in the RP and RW were significantly lower than those in the other rotations under both N1 and N2 rates. Thus,in view of the higher grain yield in the RP compared to the RW under the N1 rate, the RP rotation might be a promising practice with comparable grain yield and greater N use efficiency under reduced N input relative to the other rotations. The primary yield components of the RF and RP were identified as number of panicles m-2 and numbers of kernels panicle-1, respectively. The NAE and NPE were positively correlated with harvest index, possibly providing a useful indicator for evaluating N use efficiency.

Agronomic performance of drought-resistance rice cultivars grown under alternate wetting and drying irrigation management in southeast China

Compared to drought-susceptible rice cultivars(DSRs),drought-resistance rice cultivars(DRRs)could drastically reduce the amount of irrigation water input and simultaneously result in higher grain yield under water-saving irrigation conditions.However,the mechanisms underlying these properties are unclear.We investigated how improved agronomic traits contribute to higher yield and higher water use efficiency(WUE)in DRRs than in DSRs under alternate wetting and drying(AWD).Two DRRs and two DSRs were field-grown in 2015 and 2016 using two different irrigation regimes:continuous flooding(CF)and AWD.Under CF,no statistical differences in grain yield and WUE were observed between DRRs and DSRs.Irrigation water under the AWD regime was 275–349 mm,an amount 49.8%–56.2% of that(552–620 mm)applied under the CF regime.Compared to CF,AWD significantly decreased grain yield in both DRRs and DSRs,with a more significant reduction in DSRs,and WUE was increased in DRRs,but not in DSRs,by 9.9%–23.0% under AWD.Under AWD,DRRs showed a 20.2%–26.2% increase in grain yield and an 18.6%–24.5% increase in WUE compared to DSRs.Compared to DSRs,DRRs showed less redundant vegetative growth,greater sink capacity,higher grain filling efficiency,larger root biomass,and deeper root distribution under AWD.We conclude that these improved agronomic traits exert positive influences on WUE in DRRs under AWD.

Effects of increasing panicle-stage N on yield and N use efficiency of indica rice and its relationship with soil fertility

Because of the higher nitrogen(N)recovery efficiency(NRE)of panicle-stage fertilization compared with basal and tillering fertilization,increasing the proportion of N topdressing at the booting stage(panicleN)is recommended and commonly practiced in parts of China.To investigate the effects of increasing panicle-N on grain yield and N use efficiency(NUE)and the relationships of the increase and the rice cultivar and soil fertility status,we increased the percentage of panicle-N from 20%to 40%by correspondingly reducing the N amount applied only at the tillering stage in both high-and low-fertility blue clayey paddy fields in 2018 and 2019.Four indica cultivars with diverse panicle types were used,and their grain yield,dry matter accumulation,and NUE were compared.In high-fertility soil,increasing topdressing panicle-N from 20%to 40%reduced tillering ability and reduced the effective panicle numbers of the multi-and medium-panicle cultivars Huanghuazhan(HHZ),C Liangyouhuazhan(CHZ),and Tianyouhuazhan(THZ).These cultivars gave the greatest yield when 30%of N was supplied as panicle fertilizer,whereas the yield,NRE,N agronomic efficiency(NAE),and nitrogen physiological efficiency(NPE)of the heavy-panicle inbred cultivar Yangdao 6(YD6)continued to increase,resulting in improved dry matter accumulation and grain filling in the late growth stage.The yield,NAE,NRE,and NPE of YD6 peaked when the panicle-N constituted 40%.While in low-fertility soil,the multipanicle cultivar HHZ showed the greatest yield when 30%of fertilizer-N was applied once at the panicle initiation(PI)stage,while the medium-panicle cultivar CHZ showed the greatest yield when the panicle-N percentage was 40%.Our results suggest that the percentage of panicle-N fertilizer should not exceed 30%for multipanicle cultivars,while can be appropriately increased to 40%for heavy-panicle indica cultivars.The effect of increasing topdressing panicle-N on the yield of medium-panicle cultivars was related to soil fertility.The optimum panicle-N percentage was 30%in the high-fertility soil and 40%in the low-fertility soil.