Assessing threshold benefits of conservation tillage during drought years:

Implications for nutrient use efficiency and water qualityPierre-Andre Jacinthe1, Lin Li1, Lixin Wang1, Jia Du1, Pam Martin1, Juan Sesmero2, Dev Niyogi3

1Department of Earth Sciences, Indiana University Purdue University, Indianapolis; 2Department of Agricultural Economics, Purdue University; 3Indiana 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

Yie

ld d

iffe

rence (

NT

- C

T),

Mg h

a-1

y-1

-2

0

2

41999 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 % NTIDA

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)

Ap

ril 7

, 20

15

May

23

, 20

15

NT:

32

.5%

NT:

44

.8%