William Horwath
University of California Davis

Demands on agricultural production, range resources and fiber production continue to be a challenge and require that increased production be realized to meet the demands of an increasing population.  Exacerbating this issue is the fact that suitable area for cereal production has been decreasing at a rate of 0.3% per year due to increasing population pressure. In addition, the annual rate in the increase in cereal production per area has fallen below 1.5%, the critical value needed to ensure future food security.  Combined the loss of production area and slowing in the rate of productivity are very concerning in light of additional pressures induced by climate change.  In addition to these negative factors affecting crop production potential, the nitrogen use efficiency of crops has been declining raising concerns that biotechnology and other agronomic solutions, such as irrigation and weed control will not suffice to ensure sustainable increases per unit area of production. The decline in nitrogen use efficiency has lead to another issue, specifically the loss of reactive nitrogen to the environment.  Of special concern is the loss of nitrogen to ground water as nitrate and to the atmosphere as nitrous oxide.  Nitrous oxide is a potent greenhouse gas responsible for about 20% of the global warming potential compared to all greenhouse gas emissions combined.  Agriculture is responsible for up to 70% of total global nitrous oxide production. This dual dilemma of food insecurity and environmental impact are important drivers that need to be addressed in future agricultural research priorities.  Biotechnological and pesticide solutions have accounted for about 50% percent of the yields gains since the green revolution.  The remaining gains in food production have come from advances in fertilizer technology and cropping system management such as irrigation and soil improvement. Future research priorities in the area plant nutrition and cropping system management should address:
Challenges in water scarcity and water use efficiency will become increasingly limiting factors to crop production in the face of climate change.  Numerous studies have suggested rising atmospheric carbon dioxide levels are increasing crop water use efficiency, however, real gains in water use efficiency have been difficult to substantiate.
Decreases in nitrogen use efficiency have been attributed to many factors including increasing addition of nitrogen fertilizers, poor application timing and unaccounted for residual soil nitrogen.  In addition, an often-overlooked nitrogen uptake process is the key role of organic nitrogen in plant-microbial nutrition.
The role of crop rotations has received little attention in increasing system nitrogen use efficiency. In particular the use of cover crops to sequester residual soil nitrogen mineralization and increase potential nitrogen mineralization and availability. Crop diversity also affects the soil’s ability to maintain and sequester soil organic matter.
The role of soil organic matter, though understood as a general feature of soil productivity, is rarely managed to address sustainable nutrient cycling.  Soil organic mater affects all aspects of crop growth including supplying nutrients, affecting water availability, influencing the soil biology and many other critical factors affecting soil productivity.
A combination of bio- and agrochemical advances along with innovation in fertilizer and soil management are required to increase the rate of crop production per unit of land. Most importantly, innovation in managing nutrient availability is required to sustain crop productivity.