Effects of Long-Term Straw Management and Potassium Fertilization on Crop Yield, Soil Properties and Microbial Community in a Rice–Oilseed Rape Rotation

The present study aims to assess the influences of long-term crop straw returning and recommended potassium fertilization on the dynamic change in rice and oilseed rape yield, soil properties, bacterial and fungal alpha diversity, and community composition in a rice–oilseed rape system. A long-term (2011–2020) field experiment was carried out in a selected paddy soil farmland in Jianghan Plain, central China. There were four treatments with three replications: NP, NPK, NPS, and NPKS, where nitrogen (N), phosphate (P), potassium (K), and (S) denote N fertilizer, P fertilizer, K fertilizer, and crop straw, respectively. Results showed that long-term K fertilization and crop straw returning could increase the crop yield at varying degrees for ten years. Compared with the NP treatment, the long-term crop straw incorporation with K fertilizer (NPKS treatment) was found to have the best effect, and the yield rates increased by 23.0% and 20.5% for rice and oilseed rape, respectively. The application of NPK fertilizer for ten years decreased the bacterial and fungal alpha diversity and the relative abundance of dominant bacterial and fungal taxa, whereas continuous straw incorporation had a contradictory effect. NPKS treatment significantly increased the relative abundance of some copiotrophic bacteria (Firmicutes, Gemmatimonadetes, and Proteobacteria) and fungi (Ascomycota). Available K, soil organic matter, dissolved organic carbon, and easily oxidized organic carbon were closely related to alterations in the composition of the dominant bacterial community; easily oxidized organic carbon, dissolved organic carbon, and slowly available K were significantly correlated with the fungal community. We conclude that long-term crop straw returning to the field accompanied with K fertilizer should be employed in rice-growing regions to achieve not only higher crop yield but also the increase in soil active organic carbon and available K content and the improvement of the biological quality of farmland.

The effects of straw-returning and inorganic K fertilizer on the carbon–nitrogen balance and reproductive growth of cotton

Background Many studies have indicated that straw-returning could meet part or even all of the potassium (K) demand for crop growth in the field, but few have compared the effects of crop straw as K source and inorganic K fertilizer on carbon–nitrogen (C–N) balance of cotton and the reproductive growth. To address this, field experiments were conducted using the cotton cultivar, Siza 3, under there treatments (CK as control group one, no crop straw and inorganic K fertilizer were applied; K150 as control group two, 150 kg·ha−1 of K2O was applied; and W9000, 9 000 kg·ha−1 wheat straw, which could provide K2O about 150 kg·ha−1, was incorporated into soil). Results Although the final reproductive organ biomass did not differ between W9000 and K150, W9000 had a higher ratio of reproductive organ biomass to total biomass (RRT), suggesting that straw-returning was more conducive to the allocation of biomass to reproductive organs. The theoretical maximum biomass of reproductive organ was higher, but the average and maximum accumulation rates of reproductive organ biomass were 2.8%∼8.3% and 2.5%∼8.2% lower under W9000 than K150. Also, the duration of rapid-accumulation period for reproductive organ biomass (T) was 2.0∼2.8 d longer under W9000 than K150, which was a reason for the higher RRT under W9000. Straw-returning altered the dynamics of leaf K with the growth period, so that W9000 had a more drastic effect on leaf C metabolism than K150. Consequently, lower soluble sugar/free amino acid and C/N ratios were measured under W9000 than K150 at boll-setting (BSS) and boll-opening (BOS) stages. Higher leaf net photosynthetic rate, sucrose phosphate synthase and sucrose synthase activities, and lower acid invertase activity were observed under W9000 than K150 at BSS and BOS and these were more conducive to sucrose accumulation. However, less sucrose was measured under W9000 than K150 at these stages. This should be because straw-returning promoted the assimilate transport capacity when compared with inorganic K fertilizer application, which also explained the higher RRT under W9000 than K150. The lower acid invertase activity under W9000 inhibited the conversion of sucrose to other sugars, hence lower contents of soluble sugar and starch were measured under W9000 than K150. Conclusion Under low K condition, crop straw as K source can increase the assimilate transport from source to sink, leading to lower C/N ratio in leaf and higher allocation of biomass to reproductive organs than inorganic K fertilizer.

Urea Application Rate for Crop Straw Decomposition in Temperate China

Returning straw to the field has become the most important straw utilization method in China. The aim of this research was to study the appropriate amount of nitrogen fertilizer applied when returning the straw of three major crops (wheat, rice, and corn) to the field in areas under low to high yield levels based on the demand of nitrogen for microbial decomposition of straw. Under the condition of returning 100% straw to the field, we developed the formula for calculating the nitrogen application rate and estimated the urea application rate for the three major grain crops. The results showed that returning straws of wheat, early-season rice, middle-season rice and late-season rice, and corn to the field with urea application at the rate of about 150 kg/ha, 120～135 kg/ha, 75 kg/ha, and 75～90 kg/ha, respectively, can provide sufficient nitrogen for microbial decomposition. The urea application rate for returning 100% wheat straw to the field in Huang-Huai-Hai region, Middle-Lower Yangtze region, Loess plateau region, and Northwest arid region was 135–230 kg/ha, 110–190 kg/ha, 85–145 kg/ha, and 95–165 kg/ha, respectively. 52.5–98.5 kg/ha of urea was used for 100% early rice straw returning to the field in Middle-Lower Yangtze region and South China. In addition, the urea application rate for 100% middle-late rice straw returning to the field was 95–180 kg/ha, 100–185 kg/ha, 95–175 kg/ha, and 75–140 kg/ha, respectively. The rate of urea application for 100% corn straw returning to the field in Northeast China, Huang-Huai-Hai, Northwest arid region, and Southwest China was 60–135 kg/ha, 50–115 kg/ha, 60–135 kg/ha, and 45–105 kg/ha, respectively. The amount of nitrogen fertilizer required for the total return of crop straw is not only affected by crop straw C : N, yield per unit area, and ratio of grass to grain but also affected by straw returning mode, regional nitrogen application level, and other factors. Therefore, the amount of nitrogen fertilizer should be adjusted according to the type of cropping system, soil, and climatic conditions of the specific location. This substantial N input for stimulating straw decomposition may favor N losses with nitrate leaching and nitrous oxide emissions and hold a potential for soil N eutrophication in the long term if the level is not carefully adjusted to the N requirement of the subsequent crops and changes in soil organic matter levels.

Biology and non-chemical management of Spermacoce verticillata and Spermacoce densiflora

The weed species Spermacoce densiflora DC. and Spermacoce verticillata L. have shown an increase in their occurrence in cultivated areas in the northeast region of Brazil, and field observations have reported their ineffective control with chemicals. This study aimed to evaluate the germination of S. densiflora and S. verticillata under constant (15, 20, 25, 30 and 35°C) and alternating temperatures (20–30°C) in dark and in constant light; the emergence of seedlings from seven sowing depths (0, 0.5, 1, 2, 4, 6 and 10 cm); the emergence of seedlings under five types of cover crop straw (Crotalaria juncea L., Pennisetum glaucum (L.) R. Br., Sorghum bicolor (L.) Moench, Dolichos lablab L., and Cajanus cajan L.) and four amounts (nil and the average, half and twice the amount of straw produced in the field); and germination at different aqueous cover crop extract concentrations (0, 20, 40, 60 and 100%) to measure allelopathic potential of cover crop straw. The results showed that S. densiflora has positive photoblastic behavior. The alternating temperature provided the highest percentage of germination and germination speed index (GSI) for both species. S. densiflora and S. verticillata seedling emergence decreased with an increase in depth, with no germination at a depth of 10 cm. The presence of straw impaired the emergence of seedlings of S. densiflora and S. verticillata by delaying and even preventing germination from occurring. The gradual increase in the aqueous extract concentrations was accompanied by lower percentages of germination and GSI for S. densiflora and S. verticillata.