|NAIDU, T - Acharya Ng Ranga Agricultural University (ANGRAU)|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2017
Publication Date: 6/7/2017
Citation: Timlin, D.J., Naidu, T.C., Fleisher, D.H., Reddy, V. 2017. Quantitative effects of phosphorus on maize canopy photosynthesis and biomass. Crop Science. https://doi.org/10.2135/cropsci2016.11.0970.
Interpretive Summary: Nitrogen (N) and Phosphorus (P) are primary nutrients needed for maize growth. Crop simulation models for maize such as the ARS model MAIZSIM are important tools that can be used to assess the uptake of N and P into plant matter, and export of excess nutrients to the environment. If the models are to be accurate and realistic, quantitative data on how N and P affect plant growth and development are needed to develop and test them. We carried out an experiment in outdoor growth chambers where we applied N and P at recommended and limiting rates to a maize crop. Canopy uptake of CO2 (photosynthesis) and weights of plant leaves and stems were measured. There was no significant effect of N deficit on CO2 uptake or plant weight because N rates were high and the effect of P deficit was stronger than N deficit. Plant CO2 uptake rates were much lower under P deficit than at the higher P rates. Plant biomass and leaf growth were also greatly reduced under P stress. The results suggest that photosynthesis and leaf expansion routines in a crop simulation model must be adjusted for limited P in order to simulate maize growth and development accurately. The database and other results from this research will be useful to scientists, crop modelers and policy makers involved in assessing phosphorus uptake and utilization in maize.
Technical Abstract: Simulation models for maize can assess the uptake and utilization of nitrogen (N) and phosphorus (P) and help in better managing application rates to improve nutrient use efficiency. Quantitative data, however, are needed to develop and test these models. The purpose of this experiment was to quantify the response of maize canopy photosynthesis, development and biomass to different levels of P and N under controlled conditions. Corn plants were grown in Soil Plant Atmosphere Research (SPAR) chambers in Beltsville, MD, U.S.A. with four levels of phosphorus i.e., 0(L), 0.01 (Ml), 0.05(M2) and 0.2 (H) mmol P liter-1 and three levels of nitrogen i.e., 2.0(L), 5.0(M) and 12.0(H) mmol N liter-1. The plants were grown at constant 400 µmol mole-1 C02 and 28/18 °c day/night temperatures and feritgated 3 times per day for 60 days. Canopy photosynthesis, was measured every 5 minutes throughout the crop growth period automatically using computer controlled instrumentation. Five destructive harvests for biomass were taken. No significant effect of N on biomass or photosynthesis was observed so the observations were pooled over P treatments. Net carbon assimilation in the two lowest P rates reached a maximum 20 days after emergence (0.4 g C plant-1 d-1) and did not increase. Carbon assimilation for the M2 rate was half that of the control (1.3 vs 2.5 g C plant-1 d-1) at the end of the growing period. End of season biomass was decreased by 50% in M2 and 75% in L and M1. Decreases in biomass were due to decreases in photosynthetic rate due to P stress. Based on these results it is recommended that the photosynthesis simulation routines in crop models be modified to account for P deficit and secondly leaf expansion routines.