In rice-wheat rotation systems, crop straw is usually retained in the field at land preparation in every, or every other, season. We conducted a 3-year-6-season experiment in the middle-lower Yangtze River Valley to compare the grain qualities of rice under straw retained after single or double seasons per year. Four treatments were designed as: both wheat and rice straw retained (WR), only rice straw retained (R), only wheat straw retained (W), and no straw retained (CK). The varieties were Yangmai 16 wheat and Wuyunjing 23 japonica rice. The results showed contrasting effects of W and R on rice quality. Amylopectin content, peak viscosity, cool viscosity, and breakdown viscosity of rice grain were significantly increased in W compared to the CK, whereas gelatinization temperature, setback viscosity, and protein content significantly decreased. In addition, the effect of WR on rice grain quality was similar to that of W, although soil fertility was enhanced in WR due to straw being retained in two cycles. The differences in protein and starch contents among the treatments might result from soil nitrogen supply. These results indicate that wheat straw retained in the field is more important for high rice quality than rice straw return, and straw from both seasons is recommended for positive effects on soil fertility.

What strategy of nutrient management can maintain the high and stable annual yield in rice–wheat systems under climate change? A 10-year term experiment was conducted in the rice–wheat system to investigate the effect of optimal nutrient management on crop yield and meteorological drivers of year-to-year fluctuations in rice and wheat yield. Treatments were as follows: conventional fertilization (CF, as control), fertilizer postponing (FP, with the same amount fertilization as CF and increasing rate and times of panicle fertilizer) with/without straw incorporation (including only straw returned in rice (W) or wheat (R) season, and both straw incorporation (WS), RFP (reducing amount based on FP) with/without organic fertilizer. Results showed that FP with/without straw incorporation increased 10-year average yields of rice, wheat, and annual by 4.5~6.5%, 3.8~7.2%, and 4.8~6.8%, respectively, while RFP with/without organic fertilizer did not markedly reduce wheat yield, compared with CF. Effect of optimal treatments on wheat and rice yield stability was different; among the annual yield stability in FP + WRS was the greatest due to increasing and a stable number of spikelets and dry matter accumulation (DMA) after heading. Furthermore, the coefficient of variation (CV) of DMA during rice jointing-heading (21.6~30.0%) and heading-maturity stage (20.1~27.9%) was higher than before jointing (13.9~16.7%), which were affected by day photosynthetically active radiation (explain: 26%) and the number of rainy days (explain: 34%), respectively, using Stepwise regression; in contrast, in wheat season, the fluctuation of DMA before jointing was the highest (CV: 83.8~109.9% (before jointing) vs. 61.1~97.4% (heading-mature stage) vs. 33.7~46.3% (jointing-heading period), 55% of its variations was impacted by day-night temperature differences, the number of rainy days and photosynthetically active radiation accumulation. Our finding suggested that nutrient management to increase and stable the DMA after rice jointing and before wheat jointing could maintain the high and stable annual yield in rice–wheat systems.

Along with economic advancement, diamond bit is widely used in mine exploration and engineering geological investigation. To reduce the cost of impregnated diamond bit and improve its drilling efficiency in highly abrasive formation, this paper designs a diamond bit based on matrix weakening theory, and prepares the matrix from high-grade diamond abrasives and SiC particles. Through theoretical calculation, diamond bits were designed with six different formulas of diamond concentrations and weakened SiC particle concentrations. The theoretical analysis shows that the weakened SiC particle concentration fell within 0-50%; the number of diamond particles dropped from 750,115 to 375,150, saving the diamond cost by 50%. To further explore the life, drilling efficiency, and working mechanism of diamond bit, the apparent form of bit materials was analyzed through field tests, using EPMA-1720 electron probe microanalyzer and GENSIS60 energy spectrometer. The field tests show that: the proposed bit, with 35% of matrix skeleton and 65% of bonding metal, improved the drilling efficiency of ordinary impregnated diamond bit by 68%, while reducing the service life by merely 30%. The apparent form analysis shows that: In the diamond bit designed by matrix weakening theory, the weakened SiC particles could easily fall off the matrix surface, leaving recoverable pits on the surface. The non-smooth form weakens the abrasion resistance of the matrix, reduces the contact area between the crown of the drill bit and the rock surface at the hole bottom, and increases the pressure of the crown on the rock per unit area. The fallen wakened particles participate in the abrasion of the matrix at the hole bottom, improve the grinding ability of the rock powder at hole bottom, and promote the protrusion of new diamond particles in the matrix.