Simultaneous water, nitrogen use can enhance sustainability

The results of the study carried out by two researchers from the Research Group on Agricultural Systems at Universidad Politécnica de Madrid show that management practices oriented towards reducing nitrogen losses and maintaining farm productivity should rely on optimizing nitrogen and water inputs at the same time. The coordinated improvement of both elements on agriculture has more productive and environmental advantages than separately.

Water and nitrogen availability are, globally, the most limiting crop growth factors. These two elements have a fundamental effect on food sovereignty of many regions and on the reduction of the gap between the potential food and the actual food produced in the world. Thus, problems caused by overuse of nitrogen, such as nitrate contamination of natural water reservoirs and increase of greenhouse gases in the atmosphere are mostly influenced by water management.

In addition, it has been proven strong interactions between water- and nitrogen-use efficiency in most cropping systems. Thus, the practices that seek to improve both efficiencies simultaneously are more successful than those that aim to optimize each element separately.

This study carried out by Miguel Quemada and José Luis Gabriel, researchers from Universidad Politécnica de Madrid, has assessed seven practices to improve both elements at the same time in cropping systems. Firstly, when there is crop water deficit the use of nitrogen has to be adjusted to the actual demand of the stressed crop since the plant will grow only as far as the most limiting factor allows it (water in this case), thus the rest of nitrogen remains on the soil ready to disappear from the system.

Secondly, another good practice is to improve water management in irrigated crops since excessive water use favors its loss and the dissolved nitrogen in it outside the range of the roots. Thirdly, researchers suggest the use of fertigation that consists in the application of dissolved nutrients into irrigation water, this technique has a great potential to adapt the punctual demand of water and nitrogen per plant.

Soil mulching is the fourth technique suggested in this study. When this technique is properly applied using remains of previous crops or synthetic materials, we prevent large loss of water caused by direct evaporation of the soil. Besides, soil mulching can favor the conditions to achieve a higher mineralization of soil nitrogen and it can also increase water infiltration reducing the loss of both water and nitrogen caused by soil erosion.

The fifth technique suggests the amendment of nitrogen dose taking into account the doses given by mineralization from soils and organics, thus the synthetic fertilizer can be totally replaced in some cases for instance when soil has appropriate humidity conditions.

Another technique is based on the use of species and crops that can better adapt to the cycles of climate and soil, searching for species more adapted to the water available in each region, combining species with depths of roots capable of taking water and nitrogen from where the other could not, including cover crops that can prevent the loss of nutrient and can be used as soil mulching and green manure in the future.

Finally, the seventh practice studied is the monitoring of water and nitrogen availability by using remote and proximity sensors. There exists an increasing number of affordable sensors that allow us to measure the physiological state of the plant and the availability of soil water, thus the fertilization and irrigation forecasts can be adjusted according to the deficiencies observed.

In short, the researchers of the study say, "the crop techniques addressed to reduce the loss of nitrogen, identifying the most effective practices in every case, will contribute the improvement of environment worldwide."