Assessing threshold benefits of conservation tillage during drought years: Implications for nutrient use efficiency and water quality Pierre-Andre Jacinthe 1 , Lin Li 1 , Lixin Wang 1 , Jia Du 1 , Pam Martin 1 , Juan Sesmero 2 , Dev Niyogi 3 1 Department of Earth Sciences, Indiana University Purdue University, Indianapolis; 2 Department of Agricultural Economics, Purdue University; 3 Indiana State Climate Office, Purdue University Intensive agriculture in the US Midwest has been linked to various water quality problems including eutrophication of surface waters, proliferation of nuisance algae, and expansion of the hypoxic zone in the Gulf of Mexico. Several climate models have predicted that the region’s climate will be marked by frequent periods of summer droughts interspaced with periods of excessive rainfall. These hydro- climatic alterations could exacerbate nutrient export and water quality problems in the region and beyond. For example, in the fall following the summer drought of 2012 (>90 rainless days during the critical months of May-August), unusually high nitrate (20-40 mg N L -1 ) were measured in streams draining agricultural landscapes in Iowa, Illinois and Indiana. Land-use and management can modulate the impact of climate extremes on nutrient dynamics and export. In no-till farming (NT), crop residue left on land surface can moderate soil temperature and water loss via evaporation. Thus, in drought years, crops can withstand rainfall deficit better when grown under NT than under conventional tillage (CT). Data from the long-term experimental tillage plots in Wooster (OH) has shown that the difference in corn yield between NT and CT tends to grow wider as the summer rainfall deficit increases (Fig. 1). No-till (NT) farming could provide an effective option to achieving sustainable water quality, and mitigate the impact of climate variability on crop yield, nutrient uptake, and consequently nutrient export during post-drought periods. Yet, despite growing adoption in recent decades, the total land acreage under NT remains much below the total area under CT management perhaps due to lack of awareness, among producers, of the economic and potential water quality benefits of the practice during severe droughts. Hypothesis : Due to the greater water-holding capacity of NT soils, crops can more efficiently utilize available nutrients when grown under NT compared to CT. Thus, at the end of a summer drought, the amount of residual soil mineral nutrients is significantly less in fields under NT than CT. 1. Assess the effect of NT on nutrient use efficiency, and leaching potential through simulation of drought in experimental plots under NT and CT. 2. Determine the impact of drought severity on crop yield in fields under different tillage practices through satellite-based monitoring of root-zone soil moisture and spectral analysis of vegetation canopy. 3. Conduct an analysis of the probability distribution of benefits associated with different tillage practices, and identify incentives and barriers to NT adoption. 4. Evaluate the general awareness, among producers, of the connection between climate variability, land management, crop yield and water quality. Objectives Introduction Research has been conducted in the Eagle Creek watershed in Indiana, a mixed land-use watershed predominantly agricultural in the upper reaches and suburban downstream (Fig. 2). Experimental plots have been established and fitted with rain shelters to artificially create water deficit (Fig. 2; Obj 1). Although 70-80 % rainfall reduction has been achieved, drought conditions could not be created in 2015 due an unusually wet spring and summer. Current and archived (2000-2014) satellite images from various platforms (Landsat, MODIS) have been collected. Satellite data have been used to generate maps of crop residue cover (RC). Field measurements of crop residue were made in Spring 2015 using the line-transect method. Algorithms linking spectral data and RC have been developed. Mapping of tillage practices (Fig. 3) is based either on: (i) the temporal variation in residue cover between previous year’s fall and current year’s spring, or (ii) residue cover in the weeks leading to spring planting (if RC < 30 % CT). Results obtained with the 30% RC approach are within the range reported by state agencies for this watershed (Table 2). Mapping results are validated through on-site visits and farmer interviews (Obj. 2). We will continue the analysis of archived satellite images to develop root-zone soil moisture and drought severity distribution maps across the watershed during past seasons, especially drought years (2007, 2012). Relationships will be drawn between drought severity and crop yield in fields under NT and CT and, from that analysis, a drought threshold for yield reduction will be derived for each tillage practice (higher threshold expected under NT; Obj. 3). Summary of Activity and Outlook Fig. 3. Crop residue cover map from satellite data acquired on April 7 (A) and May 23, 2015 (B). Distribution of tillage practices across the watershed at the beginning of the 2015 cropping season as determined by the 30 % RC criteria (C) and the fall-spring comparison method (D). May-August rainfall, mm 200 300 400 500 600 Yield difference (NT - CT), Mg ha -1 y -1 -2 0 2 4 1999 and 2012 Fig. 1. Difference in corn yield measured in no-till (NT) and plowed-till (CT) plots in Wooster, OH. Normal rainfall between May-August: 400 mm. Data from W.A. Dick. Year % NT IDA survey † 2010 31 14 - 30 2013 35.1 11 - 35 2014 35.7 2015 ‡ 32.5 2015 44.8 Fig. 2. Rain shelters installed at a CT and NT field to artificially created water deficit Table 1. Percent of cropland under NT in the watershed as determined by satellite data. In 2015, tillage practice was identified using both the 30% RC criteria, and the comparison method. † Indiana department of agriculture’s biennial survey in adjoining counties. Till (CT) No Till (NT) (A) (B) (C) (D) April 7, 2015 May 23, 2015 NT: 32.5% NT: 44.8%