Changes in the soil environment in the root zone will affect the growth, development and resistance of plants. The mechanism underlying the effect of drought and flood stress on rhizosphere bacterial diversity, soil metabolites and soil enzyme activity is not clear and needs further study. To analyze the dynamic changes in bacteria, metabolites and enzyme activities in the rhizosphere soil of maize under different drought-flood abrupt alternation (DFAA) stresses, the barrel test method was used to set up the ‘sporadic light rain’ to flooding (referring to trace rainfall to heavy rain) (DFAA1) group, ‘continuous drought’ to flooding (DFAA2) group and normal irrigation (CK) group from the jointing to the tassel flowering stage of maize. The results showed that Actinobacteria was the most dominant phylum in the two DFAA groups during the drought period and the rewatering period, and Proteobacteria was the most dominant phylum during the flooding period and the harvest period. The alpha diversity index of rhizosphere bacteria in the DFAA2 group during the flooding period was significantly lower than that in other stages, and the relative abundance of Chloroflexi was higher. The correlation analysis between the differential genera and soil metabolites of the two DFAA groups showed that the relative abundance of Paenibacillus in the DFAA1 group was higher during the drought period, and it was significantly positively correlated with the bioactive lipid metabolites. The differential SJA-15 bacterium was enriched in the DFAA2 group during the flooding period and were strongly correlated with biogenic amine metabolites. The relative abundances of Arthrobacter, Alphaproteobacteria and Brevibacillus in the DFAA2 group were higher compared with DFAA1 group from rewatering to harvest and were significantly positively correlated with hydrocarbon compounds and steroid hormone metabolites. The acid phosphatase activity of the DFAA1 group was significantly higher than that of the DFAA2 group during the flooding period. The study suggests that there is a yield compensation phenomenon in the conversion of ‘continuous drought’ to flooding compared with ‘sporadic light rain’, which is related to the improvement in the flooding tolerance of maize by the dominant bacteria Chloroflexi, bacterium SJA-15 and biogenic amine metabolites. These rhizosphere bacteria and soil metabolites may have the potential function of helping plants adapt to the DFAA environment. The study revealed the response of the maize rhizosphere soil environment to DFAA stress and provided new ideas for exploring the potential mechanism of crop yield compensation under DFAA.

The use of low molecular weight organic acids (LMWOAs) for the phytoremediation of heavy metals has become a promising technique. We chose five kinds of organic acids (oxalic acid (OA), acetic acid (AA), tartaric acid (TA), malic acid (MA), and citric acid (CA)) with six application rates (1, 2, 3, 4, 5, and 6 mmol/kg) and planted sunflowers (Helianthus annuus L.) in Cd-polluted soil to study the efficiency of the phytoremediation of Cd and the degree of Cd toxicity to plants. Treatment with no acid application served as the control (CK). We analyzed the plant height dry matter and the Cd and nonprotein sulfhydryl (NPT) contents in the soil and plant tissues. OA, AA, TA, MA, and CA increased plant heights by 17.6–47.40%, 21.25–39.17%, 12.5–35.52, 5.10–30.50%, and 16.15–49.17%, respectively; shoot biomass of the sunflowers was increased except with MA. NPT decreased under LMWOA application, which, in the roots, increased with the increase in root Cd under LMWOA treatment; however, there was no obvious relationship in the stems and leaves. The composition of Cd in the soil changed significantly under the LMWOA treatments compared to the CK, and the changes in carbonate Cd and Fe-Mn oxide Cd were the most prominent. The plant Cd accumulation of OA, AA, TA, MA, and CA increased by 43.31%, 55.25%, 48.69%, 0.52%, and 32.94%, respectively, and the increase in root Cd content and shoot dry matter quality promoted the increase in Cd accumulation. The LMWOAs were more likely to affect the phytoremediation of Cd by changing total P (TP) rather than total N (TN).

The global demand for cotton makes sustainable cotton production an important issue that can be improved by a better understanding of the influence of soil microbes on cotton growth. We collected cotton field soils at the seedling and flowering/boll-setting (FBS) stages in order to obtain soil properties and cotton growth indices. Bacterial and fungal community compositions were assessed by high-throughput sequencing of 16S rRNA and internal transcribed spacer genes, respectively, after which the differences in microbial functions and their influencing factors at different growth stages were analyzed. Both the diversity and composition of soil bacterial and fungal communities were found to be significantly different between the seedling and FBS stages. Microbes in the seedling stage had significantly higher richness and biomass than those in the FBS stage. Compared with the seedling stage, the stability of the soil bacterial communities was decreased. The cotton growth indices at both the seedling and FBS stages were associated with compositional shifts in the bacterial community and but not the fungal community. The abundance of specific soil microbial taxa (e.g., Pseudarthrobacter, Thiobacillus, Cephalotrichum, Chaetomium, and Fusarium) were correlated with cotton growth indices at the seedling stage, being mainly regulated by soil salinity and nitrate content. Our results highlight the importance of soil microbial communities in mediating cotton growth and will be useful in providing better strategies for the improvement of cotton agriculture.

The matching relationship between the spatial structure of cotton cluster root systems and soil-wetting patterns under mulched drip irrigation forms the theoretical basis for the technical design of mulched drip irrigation. A 2-year field experiment was conducted, in which different soil-wetting patterns were produced by setting different emitter discharge rates. The envelopes of cotton cluster root length densities were derived using the topological methodology and used to examine the effects of different soil-wetting patterns on the spatial structure of root systems and water uptake capacity within row spaces. The results showed that the root systems in rows of cotton grown under narrower and deeper soil-wetting patterns exhibited a single-peak distribution, while those under wider and shallower soil-wetting patterns exhibited a two-peak distribution. Furthermore, cotton rows grown near mulch edges experienced lower moisture stress, and wider and shallower soil-wetting patterns contributed to greater root growth rates in the vertical direction and resulted in more even potential water uptake capacities. The findings of this study revealed that wider and shallower soil-wetting patterns were more desirable for mulched drip irrigation of cotton and should be considered in the technical design of drip irrigation systems. Keywords: mulched drip irrigation, soil-wetting pattern, envelopes of cotton cluster root length densities, soil matrix suction, potential root water uptake capacity DOI: 10.25165/j.ijabe.20201305.5790 Citation: Li D W, Li M S, Shen X J, Zhou X G, Sun H, Zhao Y L, et al. Response of spatial structure of cotton root to soil-wetting patterns under mulched drip irrigation. Int J Agric & Biol Eng, 2020; 13(5): 153–162.

There are some problems in Northwest China, such as the fragile ecological environment, poor basic conditions of agricultural production, low efficiency of agricultural water use, and difficulty in clarifying the path of agricultural water use efficiency (AWUE) improvement. Based on the superefficiency data envelopment analysis (DEA) model, this study increases the amount of ‘green water’ resources in the agricultural water consumption index of the input index and increases the wastewater pollutants (total chemical oxygen demand emissions; total ammonia nitrogen emissions) in the undesired output index to measure the AWUE in the northwest region. Based on the calculation results of AWUE, combined with the modified gravity model, the connection strength of AWUE between any two provinces in Northwest China is calculated, and the spatial structure and network characteristics of AWUE in this area are analysed via the social network analysis (SNA) method. The results show that the average AWUE in 2020 is nearly two times higher than that in 2011. From the situation of the northwest provinces, the average AWUE of the five provinces is in the order of Qinghai > Shaanxi > Gansu > Ningxia > Xinjiang. The AWUE value, total population, real GDP and per capita GDP of the capital cities of the five provinces in Northwest China are the key factors for the improvement of the connection intensity of AWUE. From 2011 to 2020, the connection intensity and closeness of AWUE in Northwest China increased, and there was a clear network hierarchy. The improvement in overall AWUE in the region is mainly due to the radiation and driving effect of the central province on other provinces. Based on this, the study proposes policy recommendations for gradually realising the AWUE improvement path of the central province (Shaanxi; Gansu)—cooperation circle (Shaanxi–Ningxia; Gansu–Qinghai)—the whole region. The results provide theoretical support and a quantitative basis for optimising the spatial pattern of agricultural water resources and improving AWUE in Northwest China.