The Crop Residue Removal Threshold Ensures Sustainable Agriculture in the Purple Soil Region of Sichuan, China

Sichuan, a hilly area in southwestern China, is recommended as a bioethanol production base because of its abundant crop residue resources. However, removing the crop straw for bioethanol may negatively affect soil fertility and productivity due to the local purple soil vulnerability. To explore the impact of crop residue removal on soil fertility and productivity and meet the needs of sustainable agriculture, we conducted a crop residue removal experiment by measuring the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents, and crop yield in the purple soil region in southwest China. Soil erosion was also simulated by Revised Universal Soil Loss Equation version 2 (RUSLE 2). The results showed that soil erosion increased with the increase of the straw removal rate. Compared with 0% removal treatment, the SOC content reduced at other removal rate treatments, especially for long-term residue removal. The effect of residue removal on soil TN and TP was not consistent within one year. After two years, residue removal greater than 25% caused a decrease in TN by 1.6–3.7%, and straw removal greater than 50% caused a TP decrease by 8.5–9.3%. More than 25% of the residue removed reduced maize and canola yields, and TN and TP content. However, all crop residue removal treatments resulted in SOC content reduction and soil erosion deterioration. In conclusion, crop residue removal was not recommended due to agricultural sustainability in Sichuan, China.

Impact of Tillage and Crop Residue Management on the Weed Community and Wheat Yield in a Wheat–Maize Double Cropping System

Weeds are often harmful to crop growth due to the competition for space and resources. A field experiment containing four treatments with three replications in a complete randomized design was conducted at Yucheng Comprehensive Experiment Station, Chinese Academy of Sciences since 2008 to assess the impact of shifting from conventional tillage to no-till with crop residue management on weeds and wheat production at the North China Plain. We found that both aboveground weed density and species richness were higher under continuous no-till (NT) than conventional tillage (CT) in the regrowth and stem elongation stage of wheat growth. On the other hand, aboveground weed density in the stage of flowering and filling decreased with crop residue mulching. The density of the soil seed bank in crop residue removal treatments was significantly higher than that of crop residue retention. Besides, either crop residue mulching or incorporating into the soil significantly increased the wheat yield compared with crop residue removal regardless of tillage management. In conclusion, crop residue retention could decrease the weed density and species richness both aboveground and in the soil seed bank and inhibit the growth of broadleaf weeds by the residue layer. Moreover, crop residue retention could improve the wheat yield.

Is Crop Residue Removal to Reduce N2O Emissions Driven by Quality or Quantity? A Field Study and Meta-Analysis

In order to quantify the reduction potential for nitrous oxide (N2O) release from arable soils through the removal of crop residues, we conducted an experiment after sugar beet (Beta vulgaris L.) harvest with three treatments: (i) ploughing of the crop residues (+CR:D), (ii) returning residues after ploughing on the surface (+CR:S), and (iii) removal of the residues and ploughing (−CR). N2O fluxes were measured over 120 days in south Germany. High positive correlations between N2O fluxes and the CO2 fluxes and soil nitrate contents suggested denitrification as the main N2O source. N2O emissions in +CR:D was higher than in +CR:S (2.39 versus 0.93 kg N2O−N ha−1 120 d−1 in +CR:D and +CR:S). Residue removal in −CR reduced the N2O emission compared to +CR:D by 95% and to +CR:S by 87%. We further conducted a meta-analysis on the effect of crop residue removal on N2O emissions, where we included 176 datasets from arable soils with mainly rain fed crops. The overall effect of residue removal showed a N2O reduction of 11%. The highest N2O reduction of 76% was calculated for the removal subgroup with C/N-ratio < 25. Neither the remaining C/N-ratio subgroups nor the grouping variables “tillage” or “residue quantity” differed within their subgroup.

Sugarcane Green Harvest Effects on Arthropod Ground Predators and Lesser Cornstalk Borer (Lepidoptera: Pyralidae) Damage

A field trial was conducted to determine the effects of harvest method (green cane harvest versus preharvest burning) and different crop residue removal treatments on the populations of ground-inhabiting arthropod predators and Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) in the first ratoon crop. Neither preharvest burning nor percentage crop residue removal after green cane harvest had any significant effect on the numbers of ants (Hymenoptera: Formicidae) (F = 1.00; df = 4; P = 0.412) or spiders (Araneae) (F = 0.08; df = 4; P = 0.921) captured in pitfall traps. In contrast, crop residue levels remaining after green cane harvest significantly impacted E. lignosellus damage to the ratoon crop, with increased damage associated with lower levels of residue. Removal of ≥66% of the crop residue caused a significant (F = 132.68; df = 3; P &lt; 0.001) increase in E. lignosellus damage that would likely reduce sugarcane yield, while 33% of the residue could be removed without increasing damage. Overall, our data indicate that green cane harvesting will not affect arthropod ground predators but may reduce the risk of E. lignosellus damage.