Rice Yield and the Fate of Fertilizer Nitrogen as Affected by Addition of Earthworm Casts Collected from Oilseed Rape Fields: A Pot Experiment
November
Rice Yield and the Fate of Fertilizer Nitrogen as Affected by Addition of Earthworm Casts Collected from Oilseed Rape Fields: A Pot Experiment
Min Huang 0 1
Xuefeng Zhou 0 1
Xiaobing Xie 0 1
Chunrong Zhao 0 1
Jiana Chen 0 1
Fangbo Cao 0 1
Yingbin Zou 0 1
0 Southern Regional Collaborative Innovation Center for Grain and Oil Crops (CICGO), Hunan Agricultural University , Changsha , China
1 Editor: P. Pardha-Saradhi, University of Delhi , INDIA
The mechanism associated with improvement of soil nutritional status by oilseed rape crop, leading to better performance of rice crop, in rice-oilseed rape cropping systems is little known. The present study was aimed to test the hypothesis that earthworm casts produced during oilseed rape-growing season have positive effects on grain yield and fertilizer nitrogen (N) utilization in the subsequent flooded rice crop. A 15N-tracing pot experiment was conducted to determine the effects of earthworm casts collected from oilseed rape fields on yield attributes in rice and the fate of fertilizer N. Soil treated with earthworm casts (soil: earthworm casts = 4: 1, w/w) (EC1) produced 39% higher grain yield than soil only (EC0). EC1 had 18% more panicle number and 10% higher spikelet filling percentage than EC0. Aboveground biomass and harvest index were higher in EC1 than in EC0 by 20% and 15%, respectively. SPAD values in flag leaves were 10% and 22% higher under EC1 than EC0 at 15 and 20 days after heading, respectively. EC1 had 19% higher total N uptake and 18% higher physiological N-use efficiency than EC0. These positive effects of earthworm casts on yield attributes offset negative effects of decreasing N rate from 0.74 g pot±1 (equivalent to the recommended field rate of 150 kg ha±1) to 0.44 g pot±1 (equivalent to 60% of the recommended rate). Fertilizer N retention rate was 7% higher while fertilizer N loss rate was 6% lower in EC1 than in EC0. Our study suggests that earthworm casts produced during oilseed rape-growing season are expected to have the following benefits on the subsequent flooded rice system: (1) improving growth and physiological processes in rice plants and consequently increasing rice grain yield, and (2) increasing fertilizer N retention rate and hence decreasing fertilizer N loss rate and reducing environmental risk.
-
OPEN ACCESS
Data Availability Statement: All relevant data are
within the paper.
Funding: This work was supported by the
Earmarked Fund for China Agriculture Research
System (CARS-01).
Competing Interests: The authors have declared
that no competing interests exist.
Introduction
Rice is the staple food crop for a large segment of the world population [
1
]. China is one of the
main rice production countries, and improving rice productivity in China is very important
for world food security [
2
]. In the past five decades, rice yield has more than tripled in China
[
3
]. Unfortunately, the increase in rice yield has been associated with a major decline in
nutrient use efficiency, especially nitrogen (N) [
4
]. Agronomic N use efficiency in rice systems in
China was 15±20 kg kg±1 in the early 1960s and declined to approximately 9 kg kg±1 in the
early 1980s and to only about 6 kg kg±1 in the 2000s [
5, 6, 7
]. The low N use efficiency is mainly
attributed to overfertilization [
3, 4
]. The average rate of N application for rice production in
China is 180 kg ha±1, about 75% higher than the world average [
3
]. Because of the high rate of
N application, only 20±30% of N is taken up by the rice plant and a large proportion of N is
lost to the environment [
7, 8
]. The lost N has caused substantial environmental problems such
as increased greenhouse gas emissions, enhanced N deposition and degradation of cropland
and freshwater [
4, 8, 9, 10
].
Soil quality is critical to crop productivity and nutrient use efficiency [
11
]. Improving
nutrient cycling is an important step towards stabilizing and optimizing soil quality [
4
].
Wellplanned crop rotations, as compared to continuous monoculture systems, can be expected to
promote nutrient cycling efficiency and consequently enhance crop productivity and reduce
dependence on external fertilizer inputs [
12, 13
]. In China, rice-wheat and rice-oilseed rape
are two long-established major rice-based rotation systems [
14
]. However, long-term
experiments indicate that yields of rice-wheat cropping systems are stagnant or even declining [
15
].
What is worse, N fertilizer input has been excessively high for rice in the regions with
ricewheat rotations [
8
]. In Jiangsu, a typical rice-wheat cropping province in China, the average N
rate for rice reaches 300 kg ha±1 in some counties [
3
]. By contrast, the N rate for rice is much
lower in the regions with rice-oilseed rape cropping systems. In our long-term experiment, a
high rice yield of around 10.0 t ha±1 was achieved at an N rate of 150 kg ha±1 in a rice-oilseed
rape rotation [
16, 17, 18
]. Th (...truncated)