Combining field data and modeling to better understand maize growth response to phosphorus(P) fertilizer application and soil P dynamics in calcareous soils

We used field experimental data to evaluate the ability of the agricultural production system model (APSIM) to simulate soil P availability,maize biomass and grain yield in response to P fertilizer applications on a fluvo-aquic soil in the North China Plain.Crop and soil data from a 2-year experiment with three P fertilizer application rates(0,75 and 300 kg P_(2)O_(5) ha^(–1)) were used to calibrate the model.Sensitivity analysis was carried out to investigate the influence of APSIM SoilP parameters on the simulated P availability in soil and maize growth.Crop and soil P parameters were then derived by matching or relating the simulation results to observed crop biomass,yield,P uptake and Olsen-P in soil.The re-parameterized model was further validated against 2 years of independent data at the same sites.The re-parameterized model enabled good simulation of the maize leaf area index (LAI),biomass,grain yield,P uptake,and grain P content in response to different levels of P additions against both the calibration and validation datasets.Our results showed that APSIM needs to be re-parameterized for simulation of maize LAI dynamics through modification of leaf size curve and a reduction in the rate of leaf senescence for modern staygreen maize cultivars in China.The P concentration limits (maximum and minimum P concentrations in organs)at different stages also need to be adjusted.Our results further showed a curvilinear relationship between the measured Olsen-P concentration and simulated labile P content,which could facilitate the initialization of APSIM P pools in the NCP with Olsen-P measurements in future studies.It remains difficult to parameterize the APSIM SoilP module due to the conceptual nature of the pools and simplified conceptualization of key P transformation processes.A fundamental understanding still needs to be developed for modelling and predicting the fate of applied P fertilizers in soils with contrasting physical and chemical characteristics.

Contrasting patterns of accumulation,partitioning,and remobilization of biomass and phosphorus in a maize cultivar

Maize growth,organ development,and yield formation are highly controlled by the manner in which the plant captures,partition,and remobilizes biomass and phosphorus(P).Better understanding of biomass and P accumulation,partition,and remobilization processes will improve modeling of crop resource use.However,there is still a lack of detailed data to parameterize the modeling of these processes,particula rly for modern maize cultivars.A two-year(2016 and 2017)field experiment with three P fertilization treatments(0(P0),75(P75),and 300(P300)kg P_(2)O_(5)ha^(-1))was conducted on a Fluvo-aquic soil(Quzhou,Hebei province,China)to collect data and quantify key processes for a representative modern maize cultivar(Zhengdan 958)widely grown in China.The proportions of biomass and P partitioned into various maize organs were unaffected by P application rate.Zhengdan 958 showed a much lower leaf-senescence rate than older cultivars,resulting in post-silking leaf photosynthesis being sufficient to meet grain biomass demand.In contrast,50%-85%of leaf P and 15%-50%of stem P accumulated pre-silking were remobilized into grain,in spite of the large proportion of post-silking P uptake.Our results are consistent with the theory that plants use resources according to the priority order of re-allocation from senescence followed by assimilation and uptake,with the re-translocation of reserves last.The results also enabled us to estimate the threshold P concentrations of Zhengdan 958 for modeling crop P demand.The critical leaf P concentration for individual leaves was 0.25%-0.30%,with a corresponding specific leaf P(SLP)of 75-100 mg P m^(-2).The structural P concentration for leaf was 0.01%,corresponding to an SLP of 3.8 mg P m^(-2).The maximum P concentrations of leaves and stems were 0.33%and 0.29%.The residual P concentration for stems was 0.006%.

Testing a bell-shaped function for estimation of fully expanded leaf area in modern maize under potential production conditions

Accurate leaf area simulation is critical for the performance of crop growth models. Area of fully expanded individual leaves of maize hybrids released before 1995 (defined as old hybrids) has been simulated using a bell-shaped function (BSF) and the relationship between its parameters and total leaf number (TLNO). However, modern high-yielding maize hybrids show different canopy architectures. The function parameters calibrated for old hybrids will not accurately represent modern hybrids. In this study, we evaluated these functions using a dataset including old and modern hybrids that have been widely planted in China in recent years. Maximum individual leaf area (Y_0) and corresponding leaf position (X_0) were not predicted well by TLNO (R^2= 0.56 and R^2= 0.70) for modern hybrids. Using recalibrated shape parameters a and b with values of Y_0 and X_0 for modern hybrids, the BSF accurately predicted individual leaf area (R^2= 0.95–0.99) and total leaf area of modern hybrids (R^2= 0.98). The results show that the BSF is still a robust way to predict the fully expanded leaf area of maize when parameters a and b are modified and Y_0 and X_0 are fitted. Breeding programs have led to increases in TLNO of maize but have not altered Y_0 and X_0, reducing the correlation between Y_0, X_0, and TLNO. For modern hybrids, the values of Y_0 and X_0 are hybrid-specific. Modern hybrids tend to have less-negative values of parameter a and more-positive values of parameter b in the leaf profile. Growth conditions, such as plant density and environmental conditions, also affect the fully expanded leaf area but were not considered in the original published equations. Thus, further research is needed to accurately estimate values of Y_0 and X_0 of individual modern hybrids to improve simulation of maize leaf area in crop growth models.

Strategies for improving fertilizer phosphorus use efficiency in Chinese cropping systems

A four-year project,entitled"The mechanisms of fraction transformation and high use efficiency of P fertilizer in Chinese cropping systems"commenced in 2017.The project was established to answer three key questions and looked at 17 cropping systems on ten soils.First,we asked what are the dynamics of transformation,fixation and mobilization of P fertilizers in soil-cropping systems?Second,what are the mechanisms of soil-cropmicrobe interactions by which P fertilizer can be efficiently used?Third,how to manipulate the processes of P use in cropping systems?The targets of this project are(1)to explore the mechanisms of P fixation,the pathways of loss of P availability and the threshold of migration of fertilizer P in the field;(2)to uncover mechanisms by which soil legacy P is mobilized through root physiological and morphological processes and through arbuscular mycorrhizal fungi and P-solubilizing bacteria in rhizosphere and hyphosphere;(3)to estimate the biological potential of crops for high efficiency P absorption and use;(4)to innovate new approaches for improving the efficiency of P fertilizers.The outcomes will provide theoretical support for setting standards for limitation of P fertilizer application rate in the main cropping zones of China.

A conceptual framework and an empirical test of complementarity and facilitation with respect to phosphorus uptake by plant species mixtures

Plant species have different traits for mobilizing sparingly soluble phosphorus (P) resources,which could potentially lead to overyielding in P uptake by plant species mixtures compared to monocultures due to higher P uptake as a result of resource (P) partitioning and facilitation.However,there is circumstantial evidence at best for overyielding as a result of these mechanisms.Overyielding (the outcome) is easily confused with underlying mechanisms because of unclear definitions.We aimed to define a conceptual framework to separate outcome from underlying mechanisms and test it for facilitation and complementarity with respect to P acquisition by three plant species combinations grown on four soils.Our conceptual framework describes both mechanisms of complementarity and facilitation and outcomes (overyielding of mixtures or no overyielding) depending on the competitive ability of the species to uptake the mobilized P.Millet/chickpea mixtures were grown in pots on two calcareous soils mixed with calcium-bound P (CaP) and phytate P (PhyP).Cabbage/faba bean mixtures were grown on both acid and neutral soils mixed with P-coated iron (hydr)oxide (FeP) and PhyP.Wheat/maize mixtures were grown on all four soils.Rhizosphere carboxylate concentration and acid phosphatase activity (mechanisms) as well as plant P uptake and biomass (outcome) were determined for monocultures rhizosphere and species mixtures.Facilitation of P uptake occurred in millet/chickpea mixtures on one calcareous soil.We found no indications for P acquisition from different P sources,neither in millet/chickpea,nor in cabbage/faba bean mixtures.Cabbage and faba bean on the neutral soil differed in rhizosphere acid phosphatase activity and carboxylate concentration,but showed no overyielding.Wheat and maize,with similar root exudates,showed overyielding (the observed P uptake being 22%higher than the expected P uptake) on one calcareous soil.We concluded that although differences in plant physiological traits (root exudates) provide necessary conditions for complementarity and facilitation with respect to P uptake from different P sources,they do not necessarily result in increased P uptake by species mixtures,because of the relative competitive ability of the mixed species.

Comparison of analytical procedures for measuring phosphorus content of animal manures in China

The concentration and components of manure phosphorus(P)are key factors determining potential P bioavailability and runoff.The distribution of P forms in swine,poultry and cattle manures collected from intensive and extensive production systems in several areas of China was investigated with sequential fractionation and a simplified two-step(NaHCO3-NaOH/EDTA)procedures.The mean total P concentration,determined by the sequential fractionation procedure of intensive swine,poultry and cattle manure,expressed as g·kg–1,was 14.9,13.4 and 5.8 g·kg–1,respectively,and 4.4 g·kg–1 in extensive cattle manure.In intensive swine,poultry and cattle manure about 73%,74%and 79%of total P,respectively,was bioavailable(i.e.,P extracted by H2O and NaHCO3)and 78%in extensive cattle manure.The results indicated the relative environmental risk,from high to low,of swine,poultry and cattle manure.There is considerable regional variation in animal manure P across China,which needs to be considered when developing manure management strategies.