Nutrient management in African sorghum cropping systems: applying meta-analysis to assess yield and profitability

Abstract

Declining soil fertility and limited farmer access to inorganic fertilizer frequently cause sub-optimal grain yields throughout sub-Saharan Africa. Farm productivity is also at risk from extreme weather and future climate change. Significant uncertainty remains in predicting climate in Africa, increasing the challenge of planning for climate change adaptation. Sorghum is adapted to African climate patterns and is predicted to maintain widespread suitability across different African climatic zones under climate change. Sorghum's drought tolerance and ability to withstand water logging make it an important crop for maintaining productive agroecosystems under a changing climate. Due to its status as a staple grain, improved sorghum management can provide smallholder farmers with stability in their household nutritional needs. We reviewed sorghum (Sorghum bicolor) yield trends across nutrient management scenarios using meta-analysis. We compared yield across eight nutrient management practices: (i) N-only, (ii) P-only, (iii) N and P, (iv) N and P microdose, (v) legume management, (vi) manure addition, (vii) organic matter (OM) amendment, and (viii) mixed amendment. Our review demonstrated (1) yield improvement considering all scenarios averaged 66 % relative to no nutrient inputs, (2) yield under chemical fertilizer amendment increased by 47-98 % of control yield, (3) yield under organic nutrient amendment increased by 43-87 % of control yield, and (4) the profitability of a management scenario was not solely determined by the magnitude of yield increase. For example, due to the high cost of fertilizer, addition of nitrogen (N) and phosphorus (P) generated the largest yield increase, but the lowest profit, in two of three countries analyzed. In contrast, an edible legume in rotation averaged 43 % yield improvement relative to no nutrient inputs and a net profit of US $146 to $263 per hectare. Facilitating access to both fertilizer inputs and diversified rotations has the greatest potential to increase grain yield in Africa.

Quantifying the Limitation to World Cereal Production Due To Soil Phosphorus Status

“…• Limits to global cereal production (maize, winter wheat, and rice) due to soil P status is assessed for year 2000 with process based models • As a global average, the soil P levels can sustain potential crop yields due to history and nature of global fertilizer P use • In spite of this, we estimate a global P yield gap of 22-55% that is not markedly diminished with today's global P application practice dependent on the properties of the soil underneath. Soil texture and organic content play a significant role (Tonitto & Ricker-Gilbert, 2016;Valkama et al, 2009) by changing the P buffering capacity of the soil, whereas soil metal or carbonate content (Shen et al, 2004;Takahashi & Anwar, 2007) determines the effectiveness of applied fertilizer through formation of less available P compounds. P availability is thus an important factor in sustaining crop yields, and one that is intimately tied with the soil underneath.…”

“…More importantly, yield increases due to P are highly dependent on the properties of the soil underneath. Soil texture and organic content play a significant role (Tonitto & Ricker‐Gilbert, ; Valkama et al, ) by changing the P buffering capacity of the soil, whereas soil metal or carbonate content (Shen et al, ; Takahashi & Anwar, ) determines the effectiveness of applied fertilizer through formation of less available P compounds. P availability is thus an important factor in sustaining crop yields, and one that is intimately tied with the soil underneath.…”

“…Nutrient limitation in crops is most commonly estimated in field trials (Dai et al, 2013;Dobermann et al, 1998;Gallet et al, 2003;Shen et al, 2004;Takahashi & Anwar, 2007;Tonitto & Ricker-Gilbert, 2016;Valkama et al, 2009;Wissuwa & Ae, 2001), where the crop yield is recorded and related to soil nutrient availability or the amount of applied fertilizer. It is often shown that P addition can significantly increase yields, especially through its interaction with N (V. D. Fageria, 2001).…”

Trade‐offs across productivity, GHG intensity, and pollutant loads from second‐generation sorghum bioenergy

“…We use a field data-driven crop model coupled with LCA modeling to explore the potential impacts of N management choices on biomass yields, GHG intensity, and local air and water pollutant loads from sorghumderived cellulosic ethanol produced in California's Imperial Valley. Sorghum is a heat-and drought-tolerant C 4 grass (Tonitto & Ricker-Gilbert, 2016) that thrives in the high-irradiance environment and long seasons afforded by the Imperial Valley's mild winters (Oikawa et al, 2015b). These conditions can lead to N demands exceeding those of most biofuel crops (Fazio & Monti, 2011;Schmer et al, 2014;Ruan et al, 2016) or of sorghum grown in other parts of the United States (Haankuku et al, 2014;Hao et al, 2014;Bonin et al, 2016).…”

‘Decoupling’ land productivity and greenhouse gas footprints: A review

“…Symbiotic N 2 fixation from the atmosphere by pulse crops can help to reduce the rate of synthetic N fertilizer needed to maintain N balance. The 'N sparing' effect during pulse growth and the release of N bound in crop residues contributes to the positive N outcome(Herridge, Marcellos, Felton, Turner, & Peoples, 1995); this partially substitutes fertilizer-N(Danga, Ouma, Wakindiki, & Bar-Tal, 2009;Herridge, 2017;Tonitto & Ricker-Gilbert, 2016). In many parts of the world, such as Western Australia and Western Canada, pulse crops are typically rotated with cereals (Figure 4a).…”