Effects of integrating deficit irrigation and carbonate foliar fertilizer application into the system of rice intensification

Abstract

Introduction Rice plays a key role in food availability and the economy of Tanzania. However, the rice yield gap of over 87% indicates that there are challenges of inadequate management practices for enhancing its production. In literature, there are recommendations on the use of the System of Rice Intensification (SRI) as one of the means to enhance rice yield by improving water productivity. Further, deficit irrigation is profound in increasing water productivity while having minimal or no impact on yield. Other studies have emphasized the use of the conventional fertilizers, while recent developments have recommended the use of foliar fertilizers at the various growth stages in order to enhance rice productivity.Individually, deficit irrigation, SRI and foliar fertilizer application have proved to be effective in enhancing rice yield and water productivity. However, the information on their combined effects is limitedly known. Therefore, a study was conducted to assess the effects of integrating deficit irrigation and carbonate foliar fertilizer (Lithovit) application into the System of Rice Intensification (SRI) on rice growth, yield and water productivity in addition to economic implications. Methodology This study was conducted in Mkindo Irrigation scheme in Mvomero, Morogoro, Tanzania during the dry and wet season (October 2020 to June 2021). The experiment was laid out in a split plot design with three levels of irrigation for main plots which were 100% of the irrigation water requirement (40mm) imitating the SRI alternate wetting and drying pattern and induced deficit irrigation applied at 80% and 50% of the irrigation water requirement as IR100, IR80 and IR50, respectively. Irrigation was carried out at the appearance of soil cracks in IR100. The sub-plot fertilizer treatments were five in number namely: (A) Diammonium Phosphate (DAP) and Urea (normal practice), (B) DAP, Urea and 100% of recommended foliar fertilizer (Lithovit Standard), (C) DAP and 50%(Lithovit and Urea), (D) Lithovit Standard only and (E) no fertilizer. The combined irrigation and fertilizer treatments tested were IR100A, IR100B, IR100C, IR100D, IR100E,IR80A, IR80B, IR80C, IR80D, IR80E, IR50A, IR50B, IR50C, IR50D, and IR50E. The data was analyzed using IBM SPSS version 20 at 5% probability level and mean separation done using Duncan’s multiple range test. Results and discussion The integration of deficit irrigation and carbonate foliar fertilizer application into SRI enhanced rice growth, yield and water productivity in addition to increasing benefit cost ratio (BCR). Treatment IR80 had the best overall performance followed by IR100 and IR50.However, there was no significant difference among the water applications IR100, IR80 andIR50 for all growth and yield attributes due to disruption of water regimes by heavy rainfall in both seasons. Fertilizer treatment B had the highest yield followed by A, C and D while E had the least. It was found that, IR100Battained the highest yield of 11.10 t/ha followed by IR80B (10.90t/ha) and (IR50B and IR100A)with 9.40 t/ha for the dry season.For the wet season, IR80B (6.93 t/ha) had the highest yield followed by IR50B (6.68 t/ha)and IR100B (6.6 t/ha). The least yield was attained by IR50E with 7.10 and 3.78 t/ha for the dry and wet seasons respectively. The foliar treatments (C and D) performed as good as the conventional fertilizer treatment A due to the impact of the calcium carbonate foliar fertilizers. Lithovit supplies higher concentrations of carbon dioxide than in the atmosphere especially during water stress periods thereby aiding photosynthesis hence increasing crop growth and yield. Treatment B had the highest water productivity (WP) followed by A, C, D and E. The highest and lowest WP was 0.851 kg/m3 and 0.562 kg/m3 attained by IR80B and IR80E respectively for the dry season. For the wet season, the highest and lowest WP was attained by IR50B (0.540 kg/m3) and IR50E (0.306 kg/m3). The high WP is attributed to the impact of alternate wetting and drying practice under SRI that heavily cuts down on unproductive water losses. In addition, Lithovit foliar fertilizer that acts as a long term reservoir for carbon dioxide especially during water stress periods played a key role on yield enhancement of foliar treatments. Across water regimes, the highest benefit-cost ratio (BCR) for the dry and wet seasons was 2.81 and 1.67 respectively attained by IR100.Among fertilizer treatments, the highest BCR was attained by D (3.45) and C (1.74) forthe dry and wet seasons respectively. Treatment A had the least BCR of 1.96 and 1.06 forthe dry and wet season respectively. Combination IR100D had the highest BCR of 3.82and 2.08 for the dry and wet season respectively. All BCR >1 except IR80A and IR50Aeach with a BCR of 0.97. For all growth, yield, water productivity and BCR, the dryseason performed better than the wet season.

Conclusion The integration of deficit irrigation and carbonate foliar fertilizers into SRI enhancedgrowth, yield, water productivity and BCR. Among water regimes, IR80 had the bestoverall performance. Also, the combination of foliar and basal fertilizers had the bestoverall growth, yield and WP performance. Foliar treatments also performed as good asthe conventional basal practice due to the impact of calcium carbonate fertilizers whichenhanced production following the good yield attained. In terms of BCR, foliar treatmentshad the best performance. Generally, the dry season performed better than the wet seasonfor all growth, yield and water productivity attributes due to the low temperatures in thewet season that affected crop growth and development. Therefore, incorporating deficitirrigation and carbonate foliar fertilizers into SRI farming practices is capable ofenhancing growth, yield and water productivity.