Field and simulation studies on yield, water and nitrogen dynamics and use efficiency in rice-wheat crops in sequence.

The dominant rice-wheat cropping system in the Indo-Gangetic plain faces challenges of water depletion and nitrogen pollution of groundwater as well as declining productivity caused by over irrigation and nitrogen fertilization by the farmers. To appreciate the apt use of irrigation water and nitrogen fertilizer in rice and wheat crops it is essential to explore the water and nitrogen balances as well as dynamics in these crops, involving complex interaction between weather, soil, irrigation water and nitrogen fertilizer management. The objective of the study is to quantify yield, field water balance components, water use efficiency, water productivity, water footprint, and water and nitrogen dynamics of rice and wheat crops in relation to season, varieties, irrigation regimes and nitrogen levels. Field experimentations were conducted in double split plot design along with calibrated and validated HYDRUS 1D model use for two years comprising of treatments in rice i.e. two varieties (PR122-V 1 and PR126-V 2), two irrigation regimes (2-days drainage period-I 1 and soil water suction 16 kPa-I 2) and two nitrogen levels (120-N 1 and 90-N 2 kg N ha−1); and in wheat, two varieties (Unnat PBW343-V 1 and Unnat PBW550-V 2), two irrigation (1.2 IW/CPE-I 1 and 0.9 IW/CPE-I 2) regimes and two nitrogen levels (120-N 1 and 90-N 2 kg N ha−1). The highest grain yield recorded was 7.6 t ha−1 in treatment combination of V 1 I 2 N 1 in rice and 5.4 t ha−1 in V 1 I 1 N 1 in wheat owing to better plant growth and yield attributes (biomass production, number of effective tillers, panicle length, and 1000 grain weight). Total water footprints were lower in the treatment combination of V 1 I 1 N 1 in rice and V 1 I 2 N 1 in wheat. The water budget revealed a higher percent contribution of the total water input to drainage (62 %) in rice ensuing restoration of water in the soil profile; and to evapotranspiration (ET) (100 %) in wheat ensuing water depletion. Modeling water and nitrogen dynamics showed higher root water uptake in I 2 treatment in rice and with I 1 treatment in wheat; and leaching losses of NO 3 -N under rice than wheat; and under I 2 treatment than I 1 as well as in N 1 than N 2. The V 1 I 2 N 1 treatment in rice and V 1 I 1 N 1 treatment in wheat demonstrated superior grain yield, soil water storage, and root water uptake. Conversely, V 1 I 1 N 1 treatment in rice and V 1 I 2 N 1 treatment in wheat showed higher water use efficiency and lower water footprint. It helps to evaluate the effectiveness of irrigation and nitrogen management strategies in maximizing crop productivity while minimizing environmental impacts. • HYDRUS 1D could be used for the water and nitrogen dynamics during crop growth period. • Short duration varieties + irrigation scheduling + optimal nitrogen reduced total water footprint and nitrogen losses. • In rice wheat cropping system, rice contributed 70 % of the total water footprint. • Drainage losses accounted for 61 % in rice and 27 % in wheat of total water input. [ABSTRACT FROM AUTHOR]