Yield potential, yield gaps, and water productivity

Transcription

1 Yield potential, yield gaps, and water productivity Patricio Grassini Lenny van Bussel Nairobi, June 2012

2 Overview Yield potential (Yp) and waterlimited yield potential (Yw) Yield gap (Yg) and exploitable yield gap Crop water productivity (WP)

3 Irrigated crops: yield potential (Yp) Yield potential (Yp): the yield of a cultivar when grown in environments to which it is adapted; with nutrients and water nonlimiting and with pests, diseases, weeds, lodging, and other stresses effectively controlled (Evans and Fischer, 1999). Yp also depends on crop-sowing date, cultivar maturity, and plant population density.

4 Rainfed crops: water-limited yield potential (Yw) Under rainfed condition, we refer to water-limited yield potential (Yw), which is also determined by water supply amount and distribution because most rainfed crops suffer at least short-term water deficit at some point during the growing season.

5 Little change in yield potential of maize, rice, and wheat during last decades Graybosch, R.A., Peterson, C.J., Genetic improvement in winter wheat yields in the Great Plains of North America, Crop Sci. 50: Duvick D.N, Cassman K.G., Post-green- revolution trends in yield potential of temperate maize in the northcentral United States. Crop Sci. 39: Peng, S., K.G. Cassman, S.S. Virmani, J. Sheehy, Khush, G.S., Yield potential trends of tropical rice since the release of IR8 and the challenge of increasing rice yield potential. Crop Sci. 39:

6 Yield potential and yield gaps Achieving on-farm yields near yield-potential (irrigated crops) or waterlimited yield potential (rainfed crops) require elimination of small imperfections in the management of the cropping system which are usually risky and/or not economically viable for crop producers

7 Yield Level Attainable Yield and Exploitable Yield Gap determined by: Radiation Temperature Sowing date cv maturity 75-90% Yp or Yw Exploitable yield gap (Yg) Water supply (rainfed crops) Yp or Yw Attainable Yield Average Farm Yield

8 Importance of yield potential and yield gaps at global and local scales Estimate food production potential and associated land, water, and energy requirements Identify areas with largest yield gaps and orient investment on agricultural R&D Assess production and land-use changes associated with irrigation expansion or retraction Diagnosis of current yield level and resource-use efficiency at the farm/region level Determine yield goals for management decisions such as fertilizer application

9 Example I: improve current projections of future crop yields Average US maize yield (kg ha -1 ) SOLID LINE: linear regression ( ) y = x (4) r 2 = 0.87 (P<0.01) (8) (6) (5,7) Year (1) (2) (3) (3) Extrapolation of linear regression Source: Grassini et al. (unpublished) Projections (dashed lines): (1) Evenson et al. (IMPACT) (2) Bruinsma (FAO) (3) Nelson et al. (IMPACT) (4) Reilly & Fuglie (USDA) (5) Heisey (USDA) (6) Edgerton (Monsanto) (7) Hertell (GTAP)

10 IRRIGATED RAINFED IRRIGATED RAINFED IRRIGATED RAINFED IRRIGATED RAINFED IRRIGATED RAINFED IRRIGATED RAINFED Example II: Estimating yield goals for N application Simulated irrigated and rainfed corn yield potential (t ha -1 ) using Hybrid-Maize model (Yang et al., 2004) based on 20-y weather data and site-specific management practices. Source: Grassini et al., 2009 Brookings, SD West Point, NE Area planted with corn is indicated in green 0 16 Ord, NE Akron, CO 16 Champion, NE Manhattan, KS 16 IA Maize-N a computer program that simulates fertilizer requirement (Setiyono et al., 2011) Simulation models assume perfect crop management, hence, a fraction of the yield potential (80-85%) can be taken as a reasonable yield goal

11 Farmer's yields (% of Y P) Example III: yield gaps in farmer s fields Farmer s yields expressed as percentage of simulated yield potential (Y P ). Each bar corresponds to a corn field from a subset of 123 fields in the Tri-Basin NRD. Yield potential was simulated for each field based on actual weather and management Average Y P : 234 bu ac -1 Average farmer's yield: 207 bu ac -1 (89% of Y P ) Average yield gap is 27 bu/ac Individual farmer's fields Grassini et el. (2011) Farmer s yields were, on average, 89% of yield potential

12 Measuring yield potential: a mission impossible? Well-managed field studies in which all growth limiting factors have been eliminated Replicated over a number of years and sites to obtain a reliable average of Yp or Yw Representative of the dominant cropping system in the region of interest (planting date, cultivar maturity)

13 How to estimate Yp, Yw, and Yg? Crop simulation models Boundary-function analysis Maximum yields measured in farms or experimental stations or contestwinners fields Maximum grid-yields within an agroecological zone

14 Crop models: tools to predict yield potential Daily intercepted solar radiation f (x) = solar radiation, LAI [around silking] Kernel # Length crop cycle Temperature Kernel weight Cumulative intercepted solar radiation [grain-filling] Kernel growth rate Gross assimilation Water supply Grain-filling duration Maintenance Respiration Growth respiration Dry matter production YIELD POTENTIAL

15 Simulation of crop growth I Daily simulation of crop phenology, leaf area index, light interception, photosynthesis, and partitioning of C among plant organs.

16 from:??? Simulation of crop growth II

17 from:??? Simulation of crop growth III

18 from:??? Simulation of crop growth IV

19 from:??? Simulation of crop growth V

20 from:??? Simulation of crop growth VI

21 from:??? Simulation of crop growth VII

22 from:??? Simulation of crop growth VIII

23 from:??? Simulation of crop growth IX

24 from:??? Simulation of crop growth X

25 Daily time step

26 Simulated maize yield (t ha -1 ) Simulated rice yield (kg ha -1 ) Validation of crop simulation models Crop models must be able to reproduce yields of crops that approach Yp, across a wide range of environments, without need of on-site re-calibration HYBRID MAIZE (Grassini et al., 2009) ORYZA (Kropff et al., 1993) 13 IRRIGATED RAINFED RMSE = 1.1 t ha Observed maize yield (t ha -1 ) Observed rice yield (kg ha -1 )

27 Simulated yield potential must be based on current agronomic practices within existing cropping systems. In this example, complex cropping systems with maize, rice, and wheat grown in the same year (China) and maize, soybean, wheat, and pulses (South America), some with 2 crops per year Simulation of Yp or Yw requires specification of management practices (sowing date, maturity, etc) for EACH cropping system

28 Monthly total rain (mm) Example of multiple crops in one year: maize in central Kenya 180 Long rain season Short rain season Katumani, Kenya (-1.1º, 37.1º) J F M A M J J A S O N D Month

29 Crop water productivity (WP) At the field scale, water productivity (WP) is defined as the amount of economic yield per unit of water (kg ha.mm -1 ) Many ways to calculate WP can be found in the literature; each with its own objectives and relevance Ideally, we want an estimator of WP that accounts for avoidable inefficiencies in crop, soil, and water management

30 Water productivity: which denominator? Denominator Sources of variation Limitations & relevance Transpiration (T) Evapotranspiration (T + soil evaporation) Applied irrigation and/or rainfall Soil water at planting + infiltrated water soil water at maturity* Soil water at planting + rainfall + irrigation soil water at maturity* Crop species, vapor pressure deficit, water stress on key stages for grain # determination, T partitioning between pre/post flowering phases All of the above plus crop/soil management and irrigation/rainfall pattern that affect soil evaporation All of the above plus variations in water losses through runoff, and deep drainage, and soil water left at physiological maturity Relevant for crop physiologists but not for agronomists or crop producers It doesn t account for inefficiencies from the water-input side (e.g., runoff, percolation) Partial efficiency because doesn t account for initial soil water. Relevant when runoff/percolation are unavoidable (steep terrain, sandy soils) Relevant when runoff/deep drainage can be minimized through better soil/irrigation management * Residual soil water is negligible in rainfed cropping systems with severe terminal water stress. In irrigated systems, residual soil water can be minimized through better irrigation scheduling, hence, it may be useful to include residual water in the estimation of WP.

31 Crop grain yield (Mg hā 1 ) Water productivity (WP): rainfed wheat in Australia, rainfed sunflower in Argentina and irrigated maize in USA Rainfed Wheat, Australia WP = 8.1 kg ha-mm -1 Rainfed Sunflower, Argentina WP = 3.7 kg ha-mm -1 Irrigated maize, USA WP = 14.0 kg ha-mm -1 WP estimated as the grain yieldto-total water supply ratio Total water supply (mm) Sources: Sadras et al. (2002); Grassini et al. (2009, 2011) * Total water supply includes available soil water at sowing plus in-season rainfall and applied irrigation ** Note the, due to its higher oil content, 1 kg sunflower grain is equivalent to ~1.7 kg cereal grain.

32 Going around under an umbrella interferes with one's looking up at the sky Jerzy Kosinski Thanks! Questions?