Irrigation water use efficiency in Maize production

Results

Principle Investigator: Isaac Fandika, Kasinthula Research Station, Department of Agricultural Research Services

Project Objective: Improving maize production is critical to ensuring Malawi’s food security. Enhancing irrigated maize production during Malawi’s long dry season is one method of increasing food security. The goal of this project was to identify best-bet water management and N fertilizer rate combinations for irrigated maize production on smallholder farms. Specifically, we evaluate maize response of maize to 3 different levels of N fertilizer and 3 different irrigation regimes.

Methods: Three irrigation regimes--farmers practice, stage based, and water budget--were established at Kasinthula Research Station. In each irrigation regime, 3 subplots were established, receiving 100 kg N ha-1, 125 kg N ha-1 and 150 kg N ha-1. MultispeQ measurements were taken at 6 and 12 weeks after planting. At each MultispeQ sampling date, 12 plants were measured in each plot, and a top and middle leaf were measured on each plant, though there was no filter question identifying top and middle leaves. At each sampling date, 2 data collectors measured 6 plants in each plot. The data collectors started at different locations in the field so that each plot was measured at 2 different times of day and light intensities.

The study was a complete randomized block design with 3 replicates. Sub-plots with the 3 fertilizer N rates were established in a two-way factoral arrangement within the randomized complete block design. Multiple linear regression analysis was used to account for the effects of light intensity, time of day (when the leaf was measured), block, weeks after planting, individual MultispeQ ID, fertilizer rate, and irrigation regime on SPAD, Phi2, NPQt, and LEF and effects were considered significant at p ≤ 0.05. Mean separation of different fertilizer rates and irrigation schemes were based on Tukey’s honest significant difference (HSD) test and differences were considered significant at p ≤ 0.05.

Figure

Results: Nitrogen rate had a larger impact on plant health and photosynthesis than irrigation regime in this year of the study. Using multiple linear regression and Tukey’s honest significant difference (HSD) test, SPAD and Phi2 were significantly greater at 150 kg N ha-1 than at 100 kg N ha-1 and 125 kg N ha-1 (Fig. A). The SPAD measurement is a quick measurement of relative chlorophyll content and has been correlated with leaf NO3 (Papasavvas et al., 2008). Therefore, it is not surprising that the highest N fertilizer rate led to increased SPAD values. NPQt was highly variable and therefore there were no significant differences between N rates.

The irrigation regime did not have a significant effect on SPAD, Phi2, or NPQt (Fig B). However, changing from farmers’ irrigation practices to stage-based and water budget irrigation practices appeared to increase SPAD. The effects of irrigation regime on SPAD were much smaller than for N rate, for this reason SPAD coefficients were divided by 100 to match the scale of Phi2 and NPQt coefficients in Figure A but only divided by 10 in Figure B. Decreased NPQt in the water budget regime compared to the famers practice may indicate reduced regulation of photosynthesis.

The preliminary results from this study are limited to plant health and photosynthesis data only. While there are not many statistical differences between N rates or irrigation regimes, this data may offer significant insights into the effects of chlorophyll content (SPAD), the efficiency of photosystem II (Phi2), and non-photochemical quenching (NPQt) on maize production once yield data is included in the statistical models.

Papasavvas, A., Triantafyllidis, V., Zervoudakis, G., Kapotis, G., Samaras, Y., Salahas, G., 2008. Correlation of SPAD-502 meter readings with physiological parameters and leaf nitrate content in Beta vulgaris. J. Environ. Protection Ecol. 9, 351-356