Furrow-Irrigated Rice Response to Different Pre-Flood Nitrogen Fertilizer Application Rates

Investigators: Anna Smyly and Drew Gholson

Date: 2022

Project Summary

Introduction

Rice (Oryza sativa L.) prefers to be grown in a saturated, flooded environment requiring large amounts of water throughout the growing season. Rice farmers in the Mississippi Delta extensively draw water from the Mississippi River Valley Alluvial Aquifer (MRVAA) for irrigation purposes. Research shows the aquifer is depleting at fast rates. Furrow-irrigated rice (FIR) has become an increasingly popular method of growing rice with less water. However, FIR has its drawbacks with nonuniform yields and fertility unknowns. Nitrogen (N) is the most limiting nutrient to rice and has a strong impact on rice growth and development. Plant uptake of N fertilizer applications in FIR tend to be more unpredictable due to the aerobic environment under which rice is grown. The objective of this study is to evaluate the effect of different preflood N fertilizer applications on a FIR field.

Materials and Methods

Research was conducted at the Delta Research and Extension Center in Stoneville, MS on Sharkey clay soil in 2021, 2022, and will continue in 2023. The arrangement of the experiment design was randomized complete block, including 5 pre-flood N treatments (0, 30, 60, 120, and 180 lbs. ac-1). The study was repeated 3 times. Rice variety, CLL16, was planted into 2 row plots (each 7 ft. x 50 ft.) on 38” row spacing. Fertility treatments were broadcast applied at the 4- to 5-leaf growth stage using a manual variable rate fertilizer spreader. Irrigation water delivery was initiated across all treatment plots after fertilizer treatments were applied to incorporate fertilizer treatments into the soil. Between panicle initiation and panicle differentiation, a mid-season fertilizer application was uniformly applied aerially to all rice plots. All fertilizer plots were irrigated every 3 to 5 days throughout the growing season until plots were drained for harvest. Plant height, whole plant nutrient analysis, and lodging rates were collected at harvest from non-harvest rows. Rice grain yield and milling yield measurements were collected from 2 rows at harvest for each treatment plot and analyzed using statistical software SAS.

Results and Discussion

Rice grain yield data in 2022 shows a gradual increase in yield, numerically, from the lowest N fertilizer rate of 0 lbs. of N ac-1 to the highest N fertilizer rate of 180 lbs. of N ac-1 for all three-fertility tests (Figure 1). Table 1 shows a heat map of average rice grain yields for each fertility rate within the top, middle, and bottom zones of each test. Across all 3 tests, average yield data indicated no N response in the upper zones of the treatment plots. The plots in the bottom zone of each treatment test tended to have greater yields than the other 2 zones of the treatment test.

Conclusion

Results from this study show regardless of the pre-flood N fertilizer rate, the top zone of the test plots had no N response. The upper zone of FIR tends to dry out most quickly when compared to the middle and bottom zones. This can lead to N losses and decrease plant uptake efficiency of N fertilizer applications. The study will be repeated in 2023 to further evaluate FIR response to different pre-flood N fertilizer rates and the causes of nonuniform yield throughout the 3 different zones of a FIR field.

• Topic:
• Irrigation Scheduling
• Irrigation