| Continuous double-rice (Oryza sativa L.) rotation is the major cropping system in South region of China, and its productivity greatly affects food supplies. However, problems arising from seasonal drought and improper conventional tillage and rice straw managements, have threaten the sustainability of this cropping system and a trend of declining or stagnating yields has been observed in this cropping system. Therefore, development of an effective agricultural management of soil, water and straw resources is needed to increase crop productivity and improve sustainability of rice cropping system.A field experiment has been conducted since 2003 in the seasonal drought region in Southeast China (Yujiang County, Yingtan City, Jiangxi Province), to identify economically viable rice cultivations that can alleviate seasonal drought, save water resources and improve soil fertility, thereby leading to promote high and sustainable rice yields production. According to distribution of rainfall under double-rice cropping system in this region, we set up new rice cultivation integrated with non-flooded rice cultivation and early-rice straw return mulching and no-tillage, and applied to late-rice paddy system, in order to investigate the effects of the new rice cultivations on water balance, rice growth characteristics and yields and soil fertility. Our previous study results in 2003～2006 have shown that compared with conventional flooded rice cultivation, non-flooded rice cultivation with straw mulching, and no-tillage and non-flooded rice cultivation with straw mulching under double-rice cropping system could maintain and improve rice grain yields and system productivity with less water consumption.The same field experiment after three years was conducted to elucidate the changes of soil fertility as affected by non-flooded rice cultivation with straw mulching under conventional tillage and no tillage conditions, and the productivity of late-season rice as affected by no-tillage and non-flooded rice cultivation with straw mulching. The five treatments were set up:(1) conventional flooded rice cultivation (CF, local rice cultivation); and (2) non-flooded rice cultivation with zero mulching (ZM); and (3) non-flooded rice cultivation with straw mulching (SM); and (4) no-tillage and non-flooded rice cultivation with zero mulching (N-ZM); and (5) no-tillage and non-flooded rice cultivation with straw mulching (N-SM). The objectives of our study were:(1) to determine the influences of SM and N-SM on soil bulk density and total porosity, soil organic matter and nutrients, pH, soil microbial biomass and activity, and soil enzyme activities in 2005～2007; and (2) to determine the influences of SM and N-SM on soil total organic carbon, different fractions of soil labile organic carbon and Carbon Pool Management Index (CPMI) in 2007; and (3) to determine the influences of SM on soil nitrogen transformation status during late-season rice growth periods in 2005; and (4) to investigate the late-season rice growth characteristics and grain yields in N-SM in 2007. The main results are summarized below.1. Soil fertility properties in SM and N-SM(1) In 2007 (the fifth year), soil bulk density and soil total porosity at 0～15 cm depth under SM and N-SM were similar with those under CF, and the differences were not significant. However, ZM significantly decreased soil bulk density and increased soil total porosity at 5～10 cm depth compared with CF (P<0.05). Under non-flooded rice cultivation systems, N-SM and N-ZM significantly increased soil bulk density at 5～10 cm depth compared with ZM, respectively. And soil total porosities at 5～cm depth under N-SM and N-ZM were significantly decreased compared with ZM, respectively. Compared with ZM, SM and N-ZM could significantly increase soil bulk density at 10～15 cm depth, respectively. And compared with ZM, SM and N-ZM could significantly decrease soil total porosity at 10～15 cm depth, respectively.(2) In 2005 (the third year) and 2006 (the fourth year), compared with CF, N-SM could significantly increase soil organic matter (SOM) by 4.54%～6.88%, total nitrogen (TN) by 4.58%～6.49% and alkali hydrolysable N (AH-N) by 16.34%～32.73%, respectively. In 2006, SM could significantly increase TN by 3.90% and soil available K by 15.94% compared with CF. However, ZM significantly decreased SOM by 4.43% and AH-N by 13.41% compared with CF. Under non-flooded rice cultivation systems, compared with ZM, SM and N-SM could significantly increase SOM and AH-N, respectively. In 2005 and 2006, compared with N-ZM, N-SM could significantly increase SOM and AH-N, respectively. In 2006, soil Olsen-P and available K in SM were significantly increased compared with ZM and N-ZM. (3) In 2005 and 2006, compared with CF, SM could significantly increase MBC by 9.33%～7.02%. And compared with CF, N-SM could significantly MBC by 29.89% and soil basal respiration by 14.04%～15.96%. However, ZM could significantly decrease soil microbial biomass organic carbon (MBC) by 12.62%～6.30% compared with CF. Under non-flooded rice cultivation systems, compared with ZM and N-ZM, SM and N-SM significantly increased MBC and MBC/SOC, respectively. Compared with ZM and N-ZM, N-SM could significantly increase soil basal respiration.(4) In 2005 and 2006, compared with CF, ZM and N-ZM could significantly decrease soil invertase activity by 5.89%～6.44% and 4.75%～4.83%, respectively. Compared with CF, SM and N-SM could significantly increase soil urease activity by 32.77%～9.35% and 31.09%～13.67%, and significantly increase soil invertase activity by 4.58%～5.31% and 9.17%～8.70%, respectively. Soil catalase activity and urease activity in ZM were similar with those in CF, and there were no significant difference. Under non-flooded rice cultivation systems, compared with ZM and N-ZM, SM and N-SM could significantly increase soil urease activity and invertase activity.2. Soil labile organic carbon and Carbon Pool Management Index (CPMI) in SM and N-SM(1) Along with the time of the rice cultivation applied to paddy systems, SM and N-SM could greatly increase soil total organic carbon (TOC) content compared with CF and ZM and N-ZM, respectively. The annual average values of TOC from 2005 to 2007 under SM and N-SM were higher 3.55% and 6.32% than CF, higher 7.26% and 10.14% than ZM, and higher 5.29% and 8.11% than N-ZM, respectively, and the differences were all significant (P<0.05). However, ZM could significantly decrease the annual average value of TOC from 2005 to 2007 by 3.47% compared with CF.(2) Compared with CF, SM and N-SM could significantly increase TOC by 3.87% and 7.40%, particulate organic carbon (POC,53～2000μm) by 16.55% and 32.15%, hot water-extractable organic carbon (HWC) by 29.91% and 41.12%, readily oxidizable organic carbon (ROC, oxidized by 333 mM KMnO4) by 20.11% and 41.94%, respectively. And SM and N-SM could significantly increase the percentage of different fractions of labile organic carbon to total organic carbon and CPMI compared to CF, respectively. However, compared with CF, ZM could significantly decrease the parameters above. For example, the TOC, POC, HWC and ROC contents in ZM were lower 4.62%,13.95%.17.76% and 19.04% than those in CF, respectively. Under non-flooded rice cultivation systems, compared with ZM, SM and N-SM could significantly increase TOC by 8.91% and 12.61%, respectively. Compared with ZM, SM, N-SM and N-ZM could significantly increase the different fractions of labile organic carbon contents, the percentage of labile organic carbon to TOC and CPMI.3. The characteristics of paddy soil nitrogen transformation in SM under conventional tillage(1) During late-season rice growth periods, contents of soil NH4+-N, NO3--N and mineral N were greatly affected by different rice cultivations. Compared with CF, SM and ZM could significantly decrease NH4+-N contents by 11.96%～23.44% and 24.83%～30.50% at both the pre-planting and harvest stages, respectively. However, SM and ZM could significantly increase NH4+-N contents by 29.91% and 28.86% at harvest stage, respectively. Compared with CF, SM and ZM could significantly increase soil NO3--N contents by 56.82%～115.75% and 38.77%～83.85% at late-season rice growth periods from pre-planting stage to harvest stage. Soil mineral N (the total of NH4+-N and NO3--N) contents in SM at both late-season rice pre-planting stage and harvest stage were higher 35.67% and 43.69% than those in CF and had significant difference (P<0.05), respectively. During the late-season rice growth.periods, soil NO3--N was the predominant form of soil inorganic N under SM and ZM.(2) Soil potential mineralisable N content in SM was higher 24.65% than that in ZM at harvest stage of late-season rice. Soil microbial biomass N contents in SM were higher 40.10% at heading stage than CF, and higher 28.69% at harvest stage than ZM, and the differences were significant (P<0.05), respectively. Soil urease activities in SM were higher 30.68%～30.72% than ZM, and higher 56.75%～32.94% than CF at both heading stage and harvest stage, and the difference was significant (P<0.05), respectively.(3) Correlation analysis showed that soil urease was significantly correlated with soil total N, alkali hydrolysable N, NH4+-N, NO3--N, mineral N and potential mineralisable N (P<0.05).4. The characteristics of productivity of late-season rice in N-SM(1) During late-season rice tillering periods, the plant height and tiller numbers of N-SM were similar to those of N-CF, and the difference was not significant. However, compared with N-CF, N-ZM significantly decreased plant height.(2) At heading stage of late-season rice, no-tillage and non-flooded rice cultivations (N-SM and N-ZM) could significantly decrease the area of flag leaf by 23.02% and the area of second leaf from the top by 19.13%. Compared with N-CF, N-ZM could significantly decrease the area of the third leaf from the top by 14.97%. However, there was no significant difference in the area of the third leaf from the top between N-SM and N-CF.(3) At the grain-filling stage of late-season rice, the total root tip numbers in N-SM were significantly higher than that in N-CF. Under no-tillage and non-flooded rice cultivation systems, compared with N-ZM, N-SM could significantly increase root total length, total tip numbers and root dry weight, respectively. However, the root average diameters were greatly decreased by N-SM and N-CF compared to N-ZM.(4) During the late-season rice growth periods from elongation stage to ripening stage, the above-ground dry matter of rice plants was similar between the N-SM and N-CF, and the difference was not significant. However, the above-ground dry matter of rice plants in N-SM and N-CF were higher 9.21%～26.90% and 16.70%～36.99% than those in N-ZM, and had significant difference (P<0.05), respectively.(5) The late-season rice grain yield of N-SM was similar with that of no-tillage and non-flooded rice cultivation (N-CF), and the difference was not significant. However, the late-season rice grain yields in N-SM and N-CF were higher 37.57% and 34.38% than that of N-ZM, and had significant difference (P<0.05), respectively. The effective panicles of late-season rice plants in N-SM and N-CF were significantly higher than those in N-ZM, respectively. |
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