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The utilization of crop straw resources has been highly emphasized by governments and academia in recent decades. The growing importance of straw decomposition in the wheat-maize rotation system and the remarkable diversity of accumulated information on this topic inspired us to quantitatively explore variations in the outcomes of individual studies. We conducted a data analysis of 46 experimental studies reporting the effects of agronomic measures on the straw decomposition rates of wheat (14 studies) and maize (38 studies). Statistical results showed that maize straw crushed and buried in soil with turn-over or rotary tillage can significantly increase straw decomposition rates. Further, with the increase in nitrogen input and straw burial depth in the soil, the maize straw decomposition rate increased significantly, while the amount of straw return showed the opposite trend. Among all agronomic measures in this research, burial depth has demonstrated a significant positive effect on the wheat straw decomposition rate. The random forest analysis identified decomposition time as the most important predictor of straw decomposition rates for wheat and maize. In addition, some agronomic measures and straw decomposition time jointly affect the decomposition rate of straw. In general, agronomic measures are effective factors in controlling straw decomposition in a wheat-maize rotation system. [ABSTRACT FROM AUTHOR]

In the conventional straw returning operation, the maize straw is broken into pieces of about 10 cm and degraded naturally in the farmland. Under the conventional straw returning mode, maize straw does not easily decompose quickly in cold climate conditions, which can cause a significant decrease in the dry matter accumulation rate of next maize seedlings. Therefore, it is difficult to popularize conventional straw returning in the maize-growing regions of Northeast China. In order to solve the above-mentioned problems, a new agronomic technology of straw returning is proposed in this study, and a corresponding Bionic Straw Fine Crusher is developed to match the agronomic requirements. The key function of fine-crush straw returning is to significantly increase the contact area between the straw pith and the external environment by significantly shortening the crushing length, thus accelerating the rate of straw decomposition. In this study, the differences in operational effects between fine-crush straw returning, conventional straw returning, and no returning are clarified through 6 consecutive years of field experiments. At the same time, statistical analysis of the experimental data reveals the influence of fine-crush straw returning on the dry matter accumulation of maize at the seedling stage under the conditions of different returning modes, and determines the optimal agronomic parameter combination. The results of this study show that fine-crush straw returning significantly increased the decomposition rate, soil organic matter content, and soil accumulated temperature, thus creating a seedbed more favorable for maize seedling development. The experimental results showed that the optimal crushing length values of fine-crush straw returning were 1.5 cm, 3 cm, and 1.5 cm under mulching returning, shallow burial returning, and deep tillage returning conditions, respectively. Compared with conventional straw returning and no returning operations, the fine-crush straw returning operation can increase the maximum seedling dry matter accumulation of the maize crop by 5.1 g/plant and 2.8 g/plant (shallow burial), 4.2 g/plant and 1.8 g/plant (deep tillage), and 4.3 g/plant and 1.9 g/plant (mulching returning). The findings of this study may provide a viable new agronomic technology to accelerate the spread of straw returning in maize-growing areas of Northeast China.

Straw returning is a sustainable way to utilize agricultural solid waste resources. However, incomplete decomposition of straw will cause harm to crop growth and soil quality. Currently, there is a lack of technology to timely monitor the rate of straw decomposition. Dissolved organic matter (DOM) is the most active organic matter in soil and straw is mainly immersed in the soil in the form of DOM. In order to formulate reasonable straw returning management measures , a timely monitoring method of straw decomposition rate was developed in the study. Three water treatment (60%–65%, 70%–75% and 80%–85% maximum field capacity) and two fertilizer (organic fertilizer and chemical fertilizer) were set up in the management of straw returning to the field. Litterbag method was used to monitor the weight loss rate of straw decomposition under different water and fertilizer conditions in strawberry growth stage. The changes of DOM components were determined by three-dimensional fluorescence spectroscopy (3D-EEM). From the faster decomposition period to the slower decomposition period, the main components of DOM changed from protein-like components to humus-like components. At the end of the experiment, the relative content of humus-like components under the treatment of organic fertilizer and moderate water was the highest. Convolutional neural network (CNN) combined with 3D-EEM was used to identify the decomposition speed of straw. The classification precision of neural network validation set and test are 85.7% and 81.2%, respectively. In order to predict the decomposition rate of straw under different water and fertilizer conditions, 3D-EEM data of DOM were used as the input of CNN, parallel factor analysis (PARAFAC) and fluorescence region integral (FRI), and dissolved organic carbon data were used as the input of dissolved organic carbon linear prediction. The prediction model based on CNN had the best effect (R2 = 0.987). The results show that this method can effectively identify the spectral characteristics and predict the decomposition rate of straw under different conditions of water and fertilizer, which is helpful to promote the efficient decomposition of straw. [Display omitted] • The transformation from protein-like substance to humus-like substance is related to the decomposition of straw. • Reasonable straw returning water and fertilizer management measures were formulated by monitoring straw decomposition rate. • CNN successfully identified 3D-EEM characteristics under different water and fertilizer management. • CNN using spectral features had higher predictive ability than PARAFAC, FRI and DOC linear prediction. [ABSTRACT FROM AUTHOR]

In the conventional straw returning operation, the maize straw is broken into pieces of about 10 cm and degraded naturally in the farmland. Under the conventional straw returning mode, maize straw does not easily decompose quickly in cold climate conditions, which can cause a significant decrease in the dry matter accumulation rate of next maize seedlings. Therefore, it is difficult to popularize conventional straw returning in the maize-growing regions of Northeast China. In order to solve the above-mentioned problems, a new agronomic technology of straw returning is proposed in this study, and a corresponding Bionic Straw Fine Crusher is developed to match the agronomic requirements. The key function of fine-crush straw returning is to significantly increase the contact area between the straw pith and the external environment by significantly shortening the crushing length, thus accelerating the rate of straw decomposition. In this study, the differences in operational effects between fine-crush straw returning, conventional straw returning, and no returning are clarified through 6 consecutive years of field experiments. At the same time, statistical analysis of the experimental data reveals the influence of fine-crush straw returning on the dry matter accumulation of maize at the seedling stage under the conditions of different returning modes, and determines the optimal agronomic parameter combination. The results of this study show that fine-crush straw returning significantly increased the decomposition rate, soil organic matter content, and soil accumulated temperature, thus creating a seedbed more favorable for maize seedling development. The experimental results showed that the optimal crushing length values of fine-crush straw returning were 1.5 cm, 3 cm, and 1.5 cm under mulching returning, shallow burial returning, and deep tillage returning conditions, respectively. Compared with conventional straw returning and no returning operations, the fine-crush straw returning operation can increase the maximum seedling dry matter accumulation of the maize crop by 5.1 g/plant and 2.8 g/plant (shallow burial), 4.2 g/plant and 1.8 g/plant (deep tillage), and 4.3 g/plant and 1.9 g/plant (mulching returning). The findings of this study may provide a viable new agronomic technology to accelerate the spread of straw returning in maize-growing areas of Northeast China. [ABSTRACT FROM AUTHOR]