Degree-days may be an alternative for predicting the influence of temperature on physiological aspects of plants in a changing climate. The objective of this research was to evaluate the relation between cumulative degree-days index (
Since crop growth, development, and water consumption are strongly influenced by temperature [
This strong relationship has led to the dissemination of the thermal units concept, expressed in degree-days, to describe and forecast the phenological stages and length of growing season for several crops. This index is preferred to other approaches, such as the number of days after the emergence or sowing, and represents the cumulative amount of heat necessary for a particular crop to develop [
There are different applications of the cumulative growing degree-days approach (
Different factors can influence the relationship degree-days and plant growth and development. These include temperature variation [
In this context, we introduce the bean crop, an important protein source to human consumption. In 2013, the global production reached 22.8 million tons, with Myanmar (3.7 million tons), India (3.6 million tons), Brazil (2.9 million tons), Mexico (1.3 million tons), and United Republic of Tanzania (1.1 million tons) comprising the top five dry beans production countries in the world FAO [
This crop is vulnerable to the variation of mesological factors, demanding the development and testing of empirical relations to forecast its performance considering the year-to-year variability of temperature.
Therefore, in this research, we evaluated the development, growth, and water consumption of irrigated bean (
We carried out this research at Faculdade de Engenharia Agrícola from Universidade Estadual de Campinas (UNICAMP), in Campinas city, São Paulo state, Brazil, 47°05′W, 22°54′S, and 606 m above sea level. The soil is an oxisoil, known as red Latosol, clay texture (550 g kg−1), with a mean saturated hydraulic conductivity of 70 mm h−1 and a ground slope of 0.09 m m−1 [
In 1985, eight experimental plots were initiated for measurements of soil and water loss. Each experimental plot had an area of 600 m2 (20 m wide by 30 m long) and a collector of 20 m wide. From 1986 to 1990, the soil was recovered to introduce different agricultural mechanization treatments. In the period from 1990 to 1998, only maize was cropped in the plots during the rainy season (November to February) [
The continued use of these tillage systems for eight years influenced various soil physical and chemical parameters, as reported by de Medeiros et al. [ Chisel ploughing system (CP): 0.30 m depth, followed by a light disc harrowing. Disk ploughing system (DP): three reversible disk plough operations 26′′ incorporated crop residues to 0.20 m deep. At the time of sowing, a second ploughing was carried out at 0.25 m depth, followed by a light disk harrowing. Revolving hoe system (RH): single soil tillage was carried out with a revolving hoe to 0.18 m deep, to incorporate crop residues.
On August 27th, 1999, we started the soil tillage and on August 31st the seeding and fertilization, with a population density of 25 plants m−2. The emergence was on September 7th and the harvest on November 30th or at 84 days after emergence (DAE) in all plots.
During the whole season, 203 mm of rainfall accumulated, the mean temperature was 22°C, and the mean reference evapotranspiration (
We applied moderate amounts of irrigation water, which were 251 mm, 258 mm, and 232 mm to CP, DP, and RH tillage systems, respectively. These were distributed in 9 weekly intervals, throughout the whole season. This irrigation, together with the evapotranspiration and rain from meteorological conditions, supported a water balance, assuming no deep percolation and runoff, for most of the season. Average values of water tension at a depth of 0.15 m were 17 kPa for CP and 14 kPa for DP and RH tillage systems in the period of 6–81 DAE (from September 13th to November 27th), providing similar soil humidity to all treatments.
This work was developed in a thermic time based on cumulative growing degree-days, calculated in the following way [
For this study we used 10°C for all the crop developing stages, as suggested by other authors for different crops and environmental conditions, including beans [
Every day, we monitored the phenological evolution of the crop. The phenological stages evaluated were V0 (seed germination), V2 (seedling emergence), V3 (first trifoliate), V4 (third trifoliate), R5 (pre flowering), R6 (flowering), R7 (pod development), R8 (pod filling), and R9 (ripeness) [
Bean growth and development were weekly monitored from the plots prior to harvest, by measuring leaf area (model LI-3000, LI-COR Instruments), height, canopy ground cover (GC), and above ground dry matter (DM). Leaf area index (LAI) was calculated based on measured plant density and GC was measured from the real horizontal projection of the canopy, calculated from images, taken at 1.5 meters above the surface [
Measurements of water balance components were carried out from September to November of 1999, when we calculated the actual evapotranspiration from the following equation [
We measured soil water content profiles gravimetrically in the top 0.50 m twice a week, in the plots. We estimated the upward and downward capillary using Darcy’s law as described by de Medeiros et al. [
We used the dual crop coefficients approach to simulate the water consumption by plants and compared to that measured in the water balance, as follows [
We developed equations relating
We observed that the bean crop development was independent of the soil tillage system, allowing the use of one thermal time scale for predicting phenological events (Table
Thermal time of bean crop phenological stages, cv. IAC Carioca, in Campinas city, São Paulo state, Brazil.
Phenological stage |
|
Phenological stage |
|
---|---|---|---|
V0 | 15 | R5 | 431 |
V1 | 102 | R6 | 504 |
V2 | 145 | R7 | 616 |
V3 | 176 | R8 | 695 |
V4 | 271 | R9 | 897 |
When comparing this result to those obtained by other researchers, we considered only works that adopted, over the whole cycle, the base temperature of 10°C, as reported by de Medeiros et al. [
With the same variety, others have found similar results. For example, Tisot et al. [
Flowering, corresponding to R6 stage [
Shortly after flowering in the present study, the bean crop reached 100% GC. Unlike flowering, this event differed among tillage treatments. For the treatments CP and DP, full ground cover was reached at
This result is closer to that obtained by [
After the full ground cover, the bean crop flowering continued to expand, so that the maximum LAI occurred at 51 DAE (October 28th), reaching 4.5 and 3.6 for the CP and RH treatments, respectively, at
At the same time maximum LAI was achieved, maximum plant height of 0.49 m, 0.48 m, and 0.44 m for the soil tillage systems CP, DP, and RH was measured, respectively.
Dry matter (DM) production was different among the treatments, since the chisel ploughing and revolving hoe tillage systems accumulated their maximum amounts of 509.9 and 522.3 g m−2, respectively, at 65 DAE (
Table
First degree equation (
STS |
|
|
LL | UL |
|
|
---|---|---|---|---|---|---|
CP | −371.36 | 0.98 | 0.73 | 1.24 | 0.97 |
6 |
DP | −319.57 | 0.87 | 0.49 | 1.24 | 0.91 |
6 |
RH | −337.01 | 0.88 | 0.39 | 1.37 | 0.86 |
6 |
LL: lower limit of confidence interval of the gradient line
The average growth rate of the crop at the growth linear phase, from 31 to 65 DAE, equivalent to thermal time from 442 to
These results were superior to the ones found by [
Table
Polynomial equations (
STS |
|
|
|
|
|
|
---|---|---|---|---|---|---|
Vegetal coverage percentage (%) | ||||||
CP | 109.5 | −0.716 | 1.92 × 10−3 | −1.26 × 10−6 | 11 | 0.97 |
RH | 114.5 | −0.803 | 2.05 × 10−3 | −1.31 × 10−6 | 12 | 0.97 |
DP | 116.2 | −0.763 | 1.99 × 10−3 | −1.30 × 10−6 | 11 | 0.97 |
All | 111.1 | −0.745 | 1.95 × 10−3 | −1.27 × 10−6 | 34 | 0.95 |
|
||||||
Leaf area index | ||||||
CP | −3.36 | 1.19 × 10−2 | 4.84 × 10−6 | −1.16 × 10−8 | 9 | 0.91 |
RH | −2.30 | 5.43 × 10−2 | 1.60 × 10−5 | −1.78 × 10−8 | 9 | 0.95 |
DP | −2.36 | 7.25 × 10−2 | 1.04 × 10−5 | −1.37 × 10−8 | 9 | 0.96 |
All | −3.00 | 1.01 × 10−2 | 7.27 × 10−6 | −1.28 × 10−8 | 27 | 0.93 |
|
||||||
Dry matter (g m−2) | ||||||
CP | 183.7 | −1.647 | 4.18 × 10−3 | −2.20 × 10−6 | 11 | 0.98 |
RH | 126.6 | −1.145 | 2.95 × 10−3 | −1.45 × 10−6 | 11 | 0.95 |
DP | 142.7 | −1.295 | 3.35 × 10−3 | −1.71 × 10−6 | 11 | 0.97 |
All | 153.4 | −1.383 | 3.54 × 10−3 | −1.82 × 10−6 | 33 | 0.96 |
|
||||||
Plant height (cm) | ||||||
CP | 16.00 | −0.0927 | 4.15 × 10−4 | −3.08 × 10−7 | 9 | 0.99 |
RH | 27.55 | −0.173 | 5.38 × 10−4 | −3.67 × 10−7 | 9 | 0.98 |
DP | 27.17 | −0.156 | 5.21 × 10−4 | −3.65 × 10−7 | 9 | 0.99 |
All | 23.57 | −0.141 | 4.91 × 10−4 | −3.47 × 10−7 | 27 | 0.96 |
The adjusted curves show the high significance level of the obtained relations (
We estimated daily evapotranspiration for irrigated bean crop from dual crop coefficient approach (
In this period,
Significant relations between
We calculated daily basal crop coefficient for bean crop from the following equation developed by de Medeiros et al. [
After that, we derived a relationship to estimate daily
In this period, we adopted
We measured LAI for each treatment during the late season period, when the crop begins the senescence. From these measurements we estimated
Based on the pattern of red Latosol surface drying and according to de Medeiros et al. [
Crop coefficient curve for bean crop sown in the following soil tillage systems treatments: (a) revolving hoe, (b) disk ploughing, and (c) chisel ploughing, in Campinas city, São Paulo state, Brazil.
We evaluated the performance of crop coefficient estimates based on
Observed and simulated evapotranspiration determined from dual crop coefficient related to degree-days, for bean crop sown in different soil tillage systems treatments.
We can see the strong linear relationship (
These results confirm that the use of dual crop coefficient (related to accumulated growing degree-days) and the grass reference evapotranspiration allowed a transferable way to predict water consumption for irrigated bean crop, independent of tillage system.
Finally, the main results of this study suggest that irrigated bean crop development, growth, and water consumption are very similar among the different soil tillage systems. One of the possible causes was the drip irrigation system that provided high water application efficiency and that reduced water tension on the soil profile during all the trial. These characteristics decrease the effects caused by the soil tillage systems over eight years, mainly at soil physical parameters, like bulk density. In the rainy season the effect of soil tillage systems on the crop performance is much more evident, as reported by de Medeiros et al. [
The phenological stages of irrigated bean crop were independent of the soil tillage system.
Chisel ploughing had superior GC, LAI, and DM compared to others.
The relations between crop growth parameters and accumulated growing degree-days were highly significant; however there was no statistical difference among tillage systems. Therefore, it was possible to use a single equation to forecast each crop growth parameter based on accumulated growing degree-days for irrigated beans, regardless of soil tillage systems.
Dual crop coefficients approach based on accumulated growing degree-days for irrigated bean crop allowed forecasting the total water consumption under distinct soil tillage systems. The mean difference between measured and estimated values of total evapotranspiration reached 4%.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors thank Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), for the financial support under the Process 1999/03221-9.