Abstract

                                A field experiment was conducted in B deficient soil (0.37 mg kg-1) to assess the frequency and level of B application for increasing crop yields in maize - sunflower cropping system, fate of B pools in soils system and to monitor the changes in soil fertility and productivity due to different levels and frequency of B application under continuous cropping system at Tamil Nadu Agricultural University, Coimbatore since 2012. The analysis of initial soil samples indicated that experimental soil was neutral in soil pH and free from salinity with sandy clay in texture. The grain and stover yield of maize crop varied from 5.51-8.38 and 5.16 to 8.00 t ha-1 , respectively and significantly differed with rate of B application. Among the B levels application of B @ 1.0 kg ha-1 registered the maximum grain and stover yield of 7.55 and 7.00 t ha-1 , respectively and was followed by application of 1.5 kg ha-1, however they were on par with each other. After the harvest of maize crop, sunflower was raised and harvested and the grain and stalk yields were recorded. Among the B levels, application of B @ 1.0 kg ha-1 registered the maximum seed yield of 2.33 t ha-1 respectively and was followed by application of 0.5 kg ha-1. The interaction between the rate of B application and frequency significantly differed with grain and stalk yield. Among the frequency levels, application of B to maize crop alone every year (F3) registered the maximum seed yield as compared to others. The interaction effect revealed that application of B @ 0.5 kg ha-1 to all crop registered the highest seed yield of 2.79 t ha-1 respectively. Boron fractions like available boron, specifically adsorbed B, oxide B, organically bound B, residual B status and total boron contents were analysed after the harvest of second crop. The results revealed that the available B status varied from 0.277 to 1.940 mg kg-1,specifically adsorbed B ranged from 0.190 to 1.332,oxide bound B status in soil varied from 0.127 to 0.89 mg kg-1, organically bound B status in soil varied from 0.235 to 1.644 mg kg-1, residual fraction of B varied from 41.61 to 291.8 and total boron varied from 42.44 to 297.6 mg kg-1. Boron application resulted in significant increase in maize yield as first crop and sunflower as residual crop, respectively. Among the B fractions the order was residual B >organically bound > specifically adsorbed > oxide bound B. Application of B @ 2.0 kg ha-1 significantly registered the highest available B in soil (1.038 mg kg-1) and among the frequencies, application of B to all crops registered the highest available B (1.32 mg kg-1). The actual fraction of B fertilizer removed by the crops is only 1-2 % of the total applied fertilizer through soil.

Key words : Boron fertilization, Residual fractions in soil, Maize – Sunflower, Yield.