Irrigating with cooler water does not reverse high temperature impact on grain yield and quality in hybrid rice

Rice grain yield and quality are negatively impacted by high temperature stress.Irrigation water temperature significantly affects rice growth and development,thus influencing yield and quality.The role of cooler irrigation water in counteracting high temperature induced damages in rice grain yield and quality are not explored.Hence,in the present study two rice hybrids,Liangyoupeijiu(LYPJ)and IIyou 602(IIY602)were exposed to heat stress and irrigated with water having different temperatures in a splitsplit plot experimental design.The stress was imposed starting from heading until maturity under field-based heat tents,over two consecutive years.The maximum day temperature inside the heat tents was set at 38℃.For the irrigation treatments,two different water sources were used including belowground water with cooler water temperature and pond water with relatively higher water temperature.Daytime mean temperatures in the heat tents were increased by 1.2–2.0℃ across two years,while nighttime temperature remained similar at both within and outside the heat tents.Cooler belowground water irrigation did have little effect on air temperature at the canopy level but decreased soil temperature(0.2–1.4℃)especially under control.Heat stress significantly reduced grain yield(33%to 43%),panicles m^(-2)(9%to 10%),spikelets m^(-2)(15%to 22%),grain-filling percentage(13%to 26%)and 1000-grain weight(3%to 5%).Heat stress significantly increased chalkiness and protein content and decreased grain length and amylose content.Grain yield was negatively related to air temperature at the canopy level and soil temperature.Whereas grain quality parameters like chalkiness recorded a significantly positive association with both air and soil temperatures.Irrigating with cooler belowground water reduced the negative effect of heat stress on grain yield by 8.8%in LYPJ,while the same effect was not seen in IIY602,indicating cultivar differences in their response to irrigation water temperature.Our findings reveal that irrigating with cooler belowground water would not significantly mitigate yield loss or improve grain quality under realistic field condition.The outcome of this study adds to the scientific knowledge in understanding the interaction between heat stress and irrigation as a mitigation tool.Irrigation water temperature regulation at the rhizosphere was unable to counteract heat stress damages in rice and hence a more integrated management and genetic options at canopy levels should be explored in the future.

Comparing Eight Computing Algorithms and Four Consensus Methods to Analyze Relationship between Land Use Pattern and Driving Forces

Although many computing algorithms have been developed to analyze the relationship between land use pattern and driving forces (RLPDF), little has been done to assess and reduce the uncertainty of predictions. In this study, we investigated RLPDF based on 1990, 2005 and 2012 datasets at two spatial scales using eight state-of-the-art single computing algorithms and four consensus methods in Jinjing rive catchment in Hunan Province, China. At the entire catchment scale, the mean AUC values were between 0.715 (ANN) and 0.948 (RF) for the single-algorithms, and from 0.764 to 0.962 for the consensus methods. At the subcatchment scale, the mean AUC values between 0.624 (CTA) and 0.972 (RF) for the single-algorithms, and from 0.758 to 0.979 for the consensus methods. At the subcatchment scale, the mean AUC values were between 0.624 (CTA) and 0.972 (RF) for the single-algorithms, and from 0.758 to 0.979 for the consensus methods. The result suggested that among the eight single computing algorithms, RF performed the best overall for woodland and paddy field;consensus method showed higher predictive performance for woodland and paddy field models than the single computing algorithms. We compared the simulation results of the best - and worst-performing algorithms for the entire catchment in 2012, and found that approximately 72.5% of woodland and 72.4% of paddy field had probabilities of occurrence of less than 0.1, and 3.6% of woodland and 14.5% of paddy field had probabilities of occurrence of more than 0.5. In other words, the simulation errors associated with using different computing algorithms can be up to 14.5% if a probability level of 0.5 is set as the threshold. The results of this study showed that the choice of modeling approaches can greatly affect the accuracy of RLPDF prediction. The computing algorithms for specific RLPDF tasks in specific regions have to be localized and optimized.

Spatio-Temporal Variability of Shallow Groundwater Quality in a Hilly Red-Soil Agricultural Catchment in Subtropical Central China

Groundwater quality varies not only in space but also in time. In order to analyze the spatiotemporal variety of ground water quality, the concentration of ammonium nitrogen (NH4N), nitrate nitrogen (NO3N), total nitrogen (TN) and total phosphorus (TP) in very shallow groundwater were investigated in a red-soil catchment in subtropical central China, based on a three-dimensional kriging method. The spatio-temporal analysis demonstrated that NH4N, NO3N and TP presented strong spatio-temporal autocorrelation (with a nugget-to-sill ratio of <25%) and that TN presented a moderate spatio-temporal autocorrelation (with a nugget-to-sill ratio between 25% and 75%). According to the Chinese Groundwater Quality Standards, the ratio of areas contaminated by NH4N, NO3N, TN and TP to the whole catchment was 20.05%, 1.46%, 5.07%, 5.98%, respectively. The 3D delineation of continuously dynamic variation of contaminated area indicated that the catchment’s very shallow groundwater had a moderate contamination by NH4N, slight by TN and TP, and almost non by NO3N. Although the contaminated area was very small, only occurring in small dispersed patches, a close attention should be paid to the shallow groundwater quality because local farmers obtain their domestic drinking water directly from this shallow groundwater without any treatment prior to consuming and the potential health hazard is considerable. The findings from this study highlight the importance of surveillance of the contaminated area over time for decision making to protect public health and maintain sustainable development of the catchment.

Soil phosphorus availability and rice phosphorus uptake in paddy fields under various agronomic practices

Agronomic practices affect soil phosphorus(P) availability, P uptake by plants, and subsequently the efficiency of P use. A field experiment was carried out to investigate the effects of various agronomic practices(straw incorporation, paddy water management, nitrogen(N) fertilizer dose, manure application,and biochar addition) on soil P availability(e.g., soil total P(STP), soil available P(SAP), soil microbial biomass P(SMBP), and rice P uptake as well as P use efficiency(PUE)) over four cropping seasons in a rice-rice cropping system, in subtropical central China. Compared to the non-straw treatment(control,using full dose of chemical N fertilizer), straw incorporation increased SAP and SMBP by 9.3%–18.5% and 15.5%–35.4%, respectively;substituting half the chemical N fertilizer dose with pig manure and the biochar application increased STP, SAP, and SMBP by 10.5%–48.3%, 30.2%–236.0%, and 19.8%–72.4%,respectively, mainly owing to increased soil P and organic carbon inputs;adding a half dose of N and no N input(reduced N treatments) increased STP and SAP by 2.6%–7.5% and 19.8%–33.7%, respectively, due to decreased soil P outputs. Thus, soil P availability was greatly affected by soil P input and use. The continuous flooding water regime without straw addition significantly decreased SMBP by 11.4% compared to corresponding treatments under a mid-season drainage water regime. Total P uptake by rice grains and straws at the harvest stage increased under straw incorporation and under pig manure application, but decreased under the reduced N treatments and under biochar application at a rate of 48 t ha-1, compared to the control. Rice P uptake was significantly positively correlated with rice biomass, and both were positively correlated with N fertilizer application rates, SAP, SMBP, and STP. Phosphorus use efficiency generally increased under straw incorporation but decreased under the reduced N treatments and under the manure application(with excessive P input), compared to the control. These results showed that straw incorporation can be used to increase soil P availability and PUE while decreasing the use of chemical P fertilizers. When substituting chemical fertilizers with pig manure, excess P inputs should be avoided in order to reduce P accumulation in the soil as well as the environmental risks from non-point source pollution.

Contribution of atmospheric nitrogen deposition to diffuse pollution in a typical hilly red soil catchment in southern China

Atmospheric nitrogen （hi） deposition is currently high and meanwhile diffuse N pollution is also serious in China. The correlation between N deposition and riverine N export and the contribution of N deposition to riverine N export were investigated in a typical hilly red soil catchment in southern China over a two-year period. N deposition was as high as 26.1 to 55.8 kg N/（ha-yr） across different land uses in the studied catchment, while the riverine N exports ranged from 7.2 to 9.6 kg N/（ha-yr） in the forest sub-catchment and 27.4 to 30.3 kg N/（ha.yr） in the agricultural sub-catchment. The correlations between both wet N deposition and riverine N export and precipitation were highly positive, and so were the correlations between NH-N or NO2-N wet deposition and riverine NH4-N or NO3-N exports except for NH-N in the agricultural sub-catchment, indicating that N deposition contributed to riverine N export. The monthly export coefficients of atmospheric deposited N from land to river in the forest sub-catchment （with a mean of 14%） presented a significant positive correlation With precipitation, while the monthly contributions of atmospheric deposition to riverine N export （with a mean of 18.7% in the agricultural sub-catchment and a mean of 21.0% in the whole catchment） were significantly and negatively correlated with precipitation. The relatively high contribution of N deposition to diffuse N pollution in the catchment suggests that efforts should be done to control anthropogenic reactive N emissions to the atmosphere in hilly red soil regions in southern China.

SOIL NITROGEN CYCLING AND ENVIRONMENTAL IMPACTS IN THE SUBTROPICAL HILLY REGION OF CHINA: EVIDENCE FROM MEASUREMENTS AND MODELING

The subtropical hilly region of China is a region with intensive crop and livestock production,which has resulted in serious N pollution in soil,water and air.This review summarizes the major soil N cycling processes and their influencing factors in rice paddies and uplands in the subtropical hilly region of China.The major N cycling processes include the N fertilizer application in croplands,atmospheric N deposition,biological N fixation,crop N uptake,ammonia volatilization,N_(2)O/NO emissions,nitrogen runoff and leaching losses.The catchment nutrients management model for N cycle modeling and its case studies in the subtropical hilly region were also introduced.Finally,N management practices for improving N use efficiency in cropland,as well as catchment scales are summarized.

Healthy soils for sustainable food production and environmental quality

Soil is the foundation for sustainable foodproduction and environmental protection. Created byunsustainable land management practices and a range ofsocial, economic and environmental drivers, soil degrada-tion and pollution have been an ongoing threat tointernational food security and environmental quality.Soil degradation and pollution assessments are, however,often focused on the soil itself with little scope to devisenew soil management approaches that match foodproduction systems and/or environmentalprotection.This study draws lessons from an Australia-China JointResearch Center Program, Healthy Soils for SustainableFood Production and Environmental Quality: a researchplatform that has brought together multi-disciplinaryapproaches fromworld-renowned universitiesandresearch organizations in Australia and China. To thisend, a framework is presented for future soil managementin a new way that combines excellence in research,industry and policymakers in a partnership that will ensurenot only the right focus of the research but also that high-quality outputs will be transferable to industry and end-users.

Effect of N and P fertilization on the allocation and fixation of photosynthesized carbon in paddy soil

Potted rice seedlings independently treated with N,P,and NP were continuously^(13)CO_(2) labeled to investigated the influence of N and P application on the contribution of photosynthesized C to the rhizosphere versus bulk soil and particulate organic matter(POM)versus mineral fraction(MIN).N and NP enhanced net assimilated^(13)C on day 14(D14),with maximum C assimilation occurring on day 22(D22)under NP.Aboveground biomass retained more^(13)C than belowground biomass for all treatments.^(13)C incorporation into the rhizosphere exceeded that in bulk soil,with the maximum(6-10%)found under N addition.Newly assimilated^(13)incorporated into POM increased in the rhizosphere under N and NP conditions,whereas MIN remained largely unaffected.^(13)C-MBC proportion in the total microbial biomass C(MBC)pool revealed that N and NP stimulated microbial activity to a greater degree than P.The main portion of^(13)C in the rhizosphere and bulk soil was found in POM on D14,which decreased over time due to microbial utilization.Contrastingly,root-derived ^(13)C in the MIN remained unchanged between sampling days,which indicates that the stabilization of rhizodeposits in this fraction might be the potential mechanism underlying SOM sequestration in paddy soils.

Legacy effect of elevated CO_(2) and N fertilization on mineralization and retention of rice (Oryza sativa L.) rhizodeposit-C in paddy soil aggregates

Rhizodeposits in rice paddy soil are important in global C sequestration and cycling.This study explored the effects of elevated CO_(2) and N fertilization during the rice growing season on the subsequent mineralization and retention of rhizodeposit-C in soil aggregates after harvest.Rice(Oryza sativa L.)was labeled with ^(13)CO_(2) under ambient(400 ppm)and elevated(800 ppm)CO_(2) concentrations with and without N fertilization.After harvest,soil with labeled rhizodeposits was collected,separated into three aggregate size fractions,and flood-incubated for 100 d.The initial rhizodeposit-^(13)C content of N-fertilized microaggregates was less than 65%of that of non-fertilized microaggregates.During the incubation of microaggregates separated from N-fertilized soils,3%–9%and 9%–16%more proportion of rhizodeposit-^(13)C was mineralized to ^(13)CO_(2),and incorporated into the microbial biomass,respectively,while less was allocated to soil organic carbon than in the non-fertilized soils.Elevated CO_(2) increased the rhizodeposit-^(13)C content of all aggregate fractions by 10%–80%,while it reduced cumulative ^(13)CO_(2) emission and the bioavailable C pool size of rhizodeposit-C,especially in N-fertilized soil,except for the silt-clay fraction.It also resulted in up to 23%less rhizodeposit-C incorporated into the microbial biomass of the three soil aggregates,and up to 23%more incorporated into soil organic carbon.These results were relatively weak in the silt-clay fraction.Elevated CO_(2) and N fertilizer applied in rice growing season had a legacy effect on subsequent mineralization and retention of rhizodeposits in paddy soils after harvest,the extent of which varied among the soil aggregates.

Experimental strategies to measure the microbial uptake and mineralization kinetics of dissolved organic carbon in soil

Soil organic matter turnover rates are typically estimated from mass loss of the material over time or from on rates of carbon dioxide production.In the study,we investigated a new way to characterize the concentration-dependent kinetics of amino acids used by measuring microbial uptake and mineralization of ^(14)C-alanine.We measured the depletion from soil solution after additions ^(14)C-alanine.The microbial uptake of ^(14)C-alanine from soil solution was concentration-dependent and kinetic analysis indicated the operation of at least three distinct alanine transport systems of differing affinities.Most of the ^(14)C-alanine depletion from the soil solution occurred rapidly within the first 10-30 min of the incubation after 10μM to 1 mM substrate additions.At alanine concentrations less than 250μM,the kinetic parameters for K_(m) and V_(max) of the higher-affinity transporter were 60.0μM and 1.32μmol g^(-1) DW soil h^(-1),respectively.The mineralization of alanine was determined and the half-time values for the rapid mineralization process were 45 min to 1.5 h after the addition at alanine concentrations below 1 mM.The time delay after its uptake into microbial biomass suggested that alanine uptake and subsequent respiration were uncoupled pattern.The microbial N uptake rate was calculated by microbial mineralization,and an estimated K_(m) value of 1731.7±274.6μM and V_(max )value of 486.0±38.5μmol kg^(-1)DW soil h^(-1).This study provides an alternative approach for measuring the rate of turnover of compounds that turnover very rapidly in soil.