Crop Nutrient Limitations in Intensified Cropping Sequences on the Ganges Delta Coastal Floodplains

Cropping systems in the Ganges delta coastal region are being intensified by the insertion of new high-yielding crops, but nutrient requirements for these crops have not been determined. The objective of this study was to identify the yield limiting plant nutrients for growing monsoon rice and dry season maize under intensified cropping systems of the Ganges delta coastal floodplains. Using nutrient omission design, the treatments were as follows: full nutrient supply: nitrogen (N) + phosphorus (P) + potassium (K) + sulfur (S) + zinc (Zn) + boron (B); full nutrient minus N, P, K, S, Zn, or B; plus an unfertilized control. The treatments were tested in maize-early monsoon rice (Aus)-monsoon rice (Aman) crop sequence in 2018 and 2019 at south-central Ganges delta coastal region. Two additional single experiments were also conducted at southwestern site of the region with similar treatments. At south-central region, N omission reduced grain yield compared to full nutrients treatment by 60–71% in maize, 21–42% in early monsoon rice, and 13–21% in monsoon rice. Phosphorus omission reduced maize grain yield by 33–47%. In this region for maize, N and P were identified as serious yield limiting nutrients. By contrast, monsoon rice yields were mainly constrained by N omission. Tidal floodwater has potential to supply 3–38 kg mineral-N ha −1 and 2–19 kg phosphate-P ha −1 during monsoon which reduces the magnitude of response to nutrient omission in rice compared to maize. In south-western site, the N and P omission reduced grain yield by 22.6–56.1% and 12.7–14.6%, respectively, in rice. For intensify cropping rotations in the Ganges delta coastal floodplains, increased N and P fertilization is recommended, particularly for any dry land crops added to system.