Nutrient Dynamics in Intensive Agriculture

Title: Can induced rhizosphere hydraulic-redistribution be engineered to enhance macronutrient uptake efficiency?

PI: Teamrat A. Ghezzehei, University of California Merced


Project Summary

This study seeks to test a novel nutrient management strategy that capitalizes on the ability of plant roots to redistribute rhizosphere water from where it is relatively abundant to regions of scarcity. Our over-arching hypothesis is that {\bf\em when moisture within the bulk rooting depth is not scarce, plants are able to extract nitrogen and phosphorus from drier regions}. This process is facilitated by night-time water release from roots in the dry but nutrient rich zones–a process commonly referred to as {\em hydraulic redistribution} (HR). The efficacy of the mechanism in uptake of essential macro and micro nutrients in agricultural crops, grasses and shrubs has been demonstrated by several researchers.

The proposal specifically targets one of the root causes for nutrient losses from soil: high degree of mobility in the root zone due to the elevated soil water status during crop growth. We propose to alleviate this by spatially isolating nutrients in relatively dry top soil, and relying on HR to mobilize and facilitate nutrient uptake. In this regard, we plan to test three inter-related hypotheses: (1) nutrient unavailability in wet portions of soil triggers HR and associated nutrient uptake from dry spots, (2) the nutrient uptake facilitated by HR is adequate to support crop nutrient requirement, and (3) HR can be induced by using paired surface and subsurface drip sources to supply nutrients in low -volume doses and water in high-volume dose, respectively. The hypotheses will be tested using column experiments in which alfalfa and corn will be used as test crops. Isotope tracer will be used to conclusively determine the magnitude of nutrient uptake from dry regions. The optimal combinations of water and nutrient application strategies for hypothesis 3 will be predicted {\em a priori} using 2D simulations of the columns.

This study targets the AFRI’s priority on {\em Bioenergy, Natural Resources, and Environment} (BNRE). In particular, it directly addresses the goal of Nitrogen and Phosphorus Cycling Priority Area by proposing a nutrient management practice {\em that will lead to substantial improvements in nutrient use efficiency or improvements to impaired natural resources within a managed plant production system}''. This is ahigh-risk/high-reward’’ type of project with the potential to drastically cut nutrient losses. If proven effective, the reductions in nutrient loss will benefit competitiveness and sustainability of U.S. agriculture by reducing cost. Moreover, reductions in nutrient losses will also enhance ecosystem services such as provisioning less-contaminated surface and subsurface water resources as well as better air-quality. Improved nutrient use efficiency will help in reducing impact of food production systems on greenhouse gas emissions and energy use. The goals of our research are directly applicable to California’s vast agricultural sectors that depend on high levels of chemical inputs and for slowing down pollution of groundwater.

This research will provide training and career development opportunities to one postdoctoral scholar and several undergraduate students. It will also help UC Merced scientists to actively engage with the community of farmers, farm advisors and extension specialists in our region. We are investigating how plants live in soil, where resources are patchy and scarce. This [USDA-AFRI] funded research aims to drastically cut nutrient leaks from modern intensive agriculture.