Nitrogen- It’s What’s For Dinner


Nitrogen- It's What's For DinnerAlthough plants require both macronutrients (i.e. N,P,K) and micronutrients, nitrogen (N) is the lynchpin. It is needed in the largest quantities and is most often the limiting factor for growth and production of food on smallholder farms. Phosphorus (P) is the other major growth-limiting nutrient and is an essential facilitator in ensuring plant access to N, so it should be considered in tandem. Below we discuss the role of N in relation to soil fertility and consider how it is currently recommended and supplied to smallholder farmers. We also explore how employing agroecological principles that match N supply to actual plant requirements could improve productivity, profitability, and sustainability.


  • Harnessing biological processes can improve N and P cycling efficiency and support sustainable, profitable crop production.
  • Relies on the agronomic principle that matching supply and plant N requirements, which is critical to protect natural resources.
  • A focus on managing the nutrients (N and P) needed in macro-supply is appropriate for the vast majority of smallholder farmers and soil types.
  • Nutrients such as K, S, Zn and Ca are needed in conjunction with N and P, and anomalous vegetation color or tissue distortion can be a warning sign of deficiencies, but in most cases soil organic matter mineralization and biology-mediated solubilization can supply sufficient nutrients to improve yields several fold.


N deficiency slide 1

From along-term field experiment in Makoka Experiment station, southern Malawi where in the foreground continuous, sole maize has been fertilized for two decades and soil organic matter has declined. Agroforesty tree intercrops have maintained soil nitrogen status and maize health in the adjacent plot.

  • How to develop management recommendations that take into account the complex factors that influence nitrogen supply to crops? This includes soil biology and heterogeneity, complexity of crop rotation, management history, goals of farmers and profitability.
  • Does improved soil organic matter management remain the most feasible means for smallholders to address these deficiencies? Will it be sufficient? Under what circumstances?

Learning Lab Resources:

Bonser, A.M., J.P. Lynch and S.S. Snapp. 1996 Gravitrophic response to low P and root architectural traits in common bean. New Phytologist 132:281-288.

Chikowo R, Zingore S, Snapp S, and Johnston A 2014. Farm typologies, soil fertility variability and nutrient management in smallholder farming in sub-Saharan Africa. Nutr Cycl Agroecosyst 100:1–18.

Cichy, K.A., G.V. Caldas, S.S. Snapp and M.W. Blair. 2009. QTL analysis of seed iron, zinc, and phosphorus levels in an Andean bean population. Crop Science 49:1742-1750.

Drinkwater, L.E. and S.S. Snapp. 2008. Nutrients in agroecosystems: Rethinking the management paradigm. Advances in Agronomy. 92: 163-186.


Degraded soils: Field in Zimbabwe where nitrogen losses and soil organic matter depletion has undermined crop growth, making agriculture risky.

Degraded soils: Field in Zimbabwe where nitrogen losses and soil organic matter depletion has undermined crop growth, making agriculture risky.

N fertilizer management guide produced as a multi-institution, collaborative effort of Africa RISING-Malawi, USAID, MSU, IITA, IPNI and CABI

N2Africa–  Putting nitrogen fixation to work for smallholder farmers in Africa

Extended Bibliography and Works Cited:

Bekunda, M. A. Bationo and H. Ssali. 1997. Soil fertility management in Africa: A review of selected research trials. In: R. J. Buresh, P. A. Sanchez, and F. Calhoun (Eds) American Society of Agronomy and Soil Science Society of America, Madison, WI 53711, USA. Replenishing Soil Fertility in Africa. SSSA Special Publication no. 51., pp. 63-80.

Brodrick, S.J., F. Amijee, J.A. Kipe-Nolt, and K.E. Giller. 1995. Seed analysis as a means of identifying micronutrient deficiencies of Phaseolus vulgaris L. in the tropics. Trop. Agric.(Trinidad) 72:277-284.

Burke, W., T. Jayne, and J.R. Black.  2016.  Factors explaining the low and variable profitability of fertilizer application to maize in Zambia.  Agricultural Economics, 48, 1-12.

Diarisso, T., M. Corbeels, N. Andrieu , P. Djamen, J-M Douzet, and P. Tittonel 2015 Soil variability and crop yield gaps in two village landscapes of Burkina Faso Nutr Cycl Agroecosyst DOI 10.1007/s10705-015-9705-6. 

Close up of N deficiency in maize plant.

Close up of N deficiency in maize plant.

Challenges Addressed:  Poverty and Food Insecurity, Soil Quality & Low Productivity, Poor Access to Organic and Inorganic Inputs, Socioeconomic and Political Economic Barriers, Contested Agronomy: Moving Beyond Silver Bullets, and Nitrogen, Carbon, and Phosphorus as Drivers

Tags: Agricultural Economics, Agronomy, Development, Extension, Soil Science, Sustainability Science