Phosphorus Requirements of Rice Grown in Soils With Different Sodicity

ABSTRACT

Phosphorus (P) fertilization is reported to alleviate the adverse effects of sodicity on survival of the seedlings, growth, and yield of rice. However, it is not known if required levels of Olsen's P to alleviate the adverse sodicity effects varies with increased sodicity stress. The present study, conducted at various pH values (8.0, 9.3, 9.7, and 9.9) with varying levels of P fertilization (P0.0, P0.2, P0.4, P0.6, and P0.8 kg hm^{− 2}), showed that P requirements of rice increased with increases in sodicity stress. At a pH of 8.0, 4.3 mg kg^{− 1} Olsen's P was sufficient for survival of the seedlings, but not for grain weight (6.3 mg kg^{− 1}). Seedlings required 7.0 and 9.5 mg kg^{− 1}Olsen's P to survive at pH 9.7 and 9.9, respectively. Similarly, high P levels were needed for more total and fertile tillers and spikelets numbers. One thousand (1000) grain weight and grain yield responded to 6.3, 7.7, 8.8, and 10.4 mg kg^{− 1} Olsen's P at pH values of 8.0, 9.3, 9.7, and 9.9, respectively. Total chlorophyll in the leaves was significant in P fertilized plants. At a pH of 9.7, plants with 7.9 mg kg^{− 1} Olsen's P had 52% more chlorophyll per 100 ppm sodium (Na) in the leaves compared to those at 6.3 mg kg^{− 1} Olsen's P. This could possibly be due to improved tissue tolerance to Na in P-fertilized plants. Plants fertilized with P had higher P and potassium (K) concentrations in their shoots. Olsen's P levels of 7.7 mg kg^{− 1}, 7.9 mg kg^{− 1}, and 9.5 mg kg^{− 1} were effective in restricting increases of Na (a potentially toxic ion) in shoots at pH 9.3, 9.8, and 9.9, respectively, thus helping plants have better yields.

Keywords:

• chlorophyll
• fertilization
• pH
• phosphorus
• rice
• sodicity

ACKNOWLEDGMENTS

The authors are grateful to the Director, Central Soil Salinity Research Institute, and Head, Division of Crop Improvement, for their keen interest and facilities provided for this work. The technical assistance of the late Shiv Kumar in analyzing soil and plant samples is duly acknowledged.