ORYZA2000 v2.00 (May 2003) - Aerobic and upland rice

ORYZA2000 is a model for lowland rice. A start has been made to make the model suitable for upland rice and ‘aerobic rice’ as well. Aerobic rice is rice grown in non-puddled and nonflooded soil (just like upland rice), but with higher inputs such as supplementary irrigation and fertilizers. Aerobic rice varieties differ from upland rice varieties in the sense that they are responsive to inputs and have a higher yield potential. Upland rice varieties are targeted for the unfavourable uplands, where soil conditions are adverse (poor physical and chemical properties), severe drought occurs, and farmers generally apply no to very little external inputs such as fertilizer. Yields are generally very low (around 1 t ha-1) but stable to reduce risk. Aerobic rice is targeted at more favourable uplands and water-short lowlands, and has yield potentials of up to 6 t ha-1. More details about aerobic rice are given by Bouman (2001), Wang Huaqi et al. (2002) and Yang Xiaoguang et al. (2002). 

The first adaptation of ORYZA2000 is the inclusion of the models SAHEL and SAWAH that can simulate the water balance for upland soils (see above). The second is the inclusion of a special water-stress module. Until more research has been done, it is assumed that variety-specific differences between lowland, upland and aerobic rice (beside drought-sensitivity) can be accounted for by adaptation of parameters in the crop data file. The choice to simulate lowland rice or upland/aerobic rice is set in the experimental data file with the switch

RICETYPE: 

*--------------------------------------------------------------------*

* 1. Selection of modes of running                                   *

*--------------------------------------------------------------------*

*--  RICETYPE is to select lowland rice or aerobic/upland rice

RICETYPE = 'LOWLAND'   ! Lowland rice

*RICETYPE = 'AEROBIC'   ! Upland or aerobic rice

Drought-stress module

Depending on the selection of RICETYPE, either the original drought-stress routine WSTRESS is called in the subroutine MODELS, or the new drought-stress routine WSTRESSAEROBIC:

!-----Calculate drought stress factors

IF (PRODENV.EQ.'WATER BALANCE') THEN

!     Lowland rice drought stress routine

IF (RICETYPE.EQ.'LOWLAND') THEN

CALL WSTRESS (ITASK,  DELT, OUTPUT, IUNITD, IUNITL, FILEI1,&

TRC, ZRT, TKL, NL, CROPSTA, &

WCLQT, WCWP, MSKPA,               &

TRW, TRWL,LRSTRS, LDSTRS, LESTRS, PCEW, CPEW)

ELSE IF (RICETYPE.EQ. 'AEROBIC') THEN

!         Upland/aerobic rice drought stress routine

CALL WSTRESSAEROBIC (ITASK, DELT, OUTPUT, IUNITD, IUNITL, &

FILEI1, TRC, ZRT, TKL, NL, CROPSTA, &

WCLQT, WCWP, WCFC, WCST, &

TRW, TRWL, LRSTRS, LDSTRS, LESTRS, PCEW, CPEW)

END IF

ELSE IF (PRODENV.EQ.'POTENTIAL') THEN

CALL WNOSTRESS(NL,TRW, TRWL,LRSTRS, LDSTRS, LESTRS, PCEW, CPEW)

END IF

The drought-stress routine WSTRESSAEROBIC is adapted from the calculation procedure for the effects of drought on wheat as included in the model SUCROS97 (van Laar et al., 1997). The underlying assumption is that aerobic rice varieties behave in much the same way as wheat. This assumption, however, remains still to be tested and experiments are currently underway to do so. Users of ORYZA2000 can opt to either test this new drought-stress routine, or to use the original WSTRESS routine and adapt the drought-related parameters for lowland rice in the crop data file.

In WSTRESSAEROBIC, only the effects of drought on transpiration and partitioning of assimilates are taken into account and the other stress factors are made inactive (set to unity):

LESTRS = 1.

LRSTRS = 1.

LDSTRS = 1. 

The effect of drought on transpiration is the factor PCEW, just as in WSTRESS. The factor on partitioning of assimilates is CPEW and its functioning is explained in Section 4 (see below). The following text to explain the calculations of PCEW and CPEW is adapted from van Laar et al. (1997), Chapter 2.18.

 “Both water and air must be present in sufficient amounts in the soil for optimal uptake of soil water by roots. Since water content (WCL, q) and air content are complementary (soil porosity), the dependence of actual water uptake rate on soil water content shows an optimum (Feddes et al., 1978). Starting from wilting point (qwp), water uptake rate first rises linearly with increasing soil water content until it reaches the potential transpiration rate (the evaporative demand, Tm). The water content at which this occurs is called the critical soil water content qc. Transpiration rate remains at its potential level over a range of water contents reaching to well over field capacity. At some point beyond field capacity (qfc), transpiration is hampered again. The shape of this response curve is depicted in Figure 1, where the actual transpiration rateT is given scaled to the potential transpiration rate Tm. In contrast to Feddes et al. (1978), not soil water potential, but soil water content is chosen as the independent variable (Gollan et al., 1986; Schulze, 1986). In the computational procedure, the current value of water content determines which linear segment must be used. 

It is convenient to scale water content in the lower dry part as a fraction of the range qfc - qwp, to the so-called reduced water content (Bresler, 1991): 

Table 5. Characteristic potential transpiration rates (see text for explanation for five crop groups according to Driessen (1986). (Source: Doorenbos et al., 1978).

The critical moisture content qc, which denotes the transition from water-limited to potential transpiration rate is not at a fixed value. Restriction of water uptake rate due to water shortage starts at a higher water content when potential transpiration rate is higher, in other words qc then shifts to higher values. This phenomenon was documented by Denmead & Shaw (1962). Driessen (1986) listed the dependence of the relative position of this point in his Table 20, for five groups of plants that differ in drought sensitivity. This table can be summarized in the following way: 

i)    The crop groups are characterized by the potential transpiration rate at which the critical soil water content qc is just halfway wilting point and field capacity, in other words where S is 0.5. This characteristic potential transpiration rate TS=0.5 is given in Table 5 for the five crop groups of Table 20 of Driessen (1986). 

ii)   The soil water depletion fraction p is then calculated as: 

p = TS=0.5 / (Tm + TS=0.5)

or

1 - p = Tm / ( Tm + TS=0.5)

       The soil water content at which transpiration starts to fall short of the potential, the so-called critical soil water content, is given by: 

qc = qwp + (1 - p)  (qfc - qwp) 

iii)   The ratio between actual transpiration rate in the lower, dry part of the curve and the potential rate is now given by:

                           After substitution of the equation for p we find a simple expression for the actual transpiration rate:

 T = (Tm + TS=0.5) S

This latter expression is not actually used in the program, but the ratio fr is used instead (PCEW). Here it serves to show the resulting dependence of actual transpiration on the two environmental conditions, potential rate Tm and actual water content q(WCL), on the two soil parameters qfc and qwp, and on the plant parameter TS=0.5.

The effect of drought on assimilate partitioning, CPEW, equals the value of PCEW. 

The effect of availability of soil water on uptake in a compartment is presented by a factor (WSE1-4), with a value between 0.0 and 1.0. Figure 1 schematically shows the relation between this stress factor and soil water content. The WSE-factors are computed by a function that requires as inputs, the water content in the soil layer (WCL), the soil depletion factor (P), the water contents at field capacity (WCFC), wilting point (WCWP) and saturation (WCST), and the sensitivity coefficient for waterlogging (WCWET; being absent for rice). In this function, the critical water content (WCCR) is first calculated on the basis of the critical transpiration rate and P.”

Figure 1. Water stress factor (WSE) as a function of soil moisture content. Wilting point (WCWP, qwp), field capacity (WCFC, qfc) and saturation (WCST, qst) are soil characteristics. Values for WCCR depend on the potential transpiration/leaf area ratio and the sensitivity. For rice, WCWET does not apply and WSE stays 1 up to saturation (WCST).

References

Bouman BAM. 2001. Water-efficient management strategies in rice production. International Rice Research Notes 16.2, pp. 17-22 (IRRI, Los Baños, Philippines)

Bresler, E., 1991. Soil spatial variability. In: Eds J. Hanks & J.T. Ritchie, Modeling plant and soil systems. ASA/CSSA/SSSA Publishers, Madison (WI), Agronomy Monograph 31:145-180.

Brouwer R. 1962. Some aspects of the equilibrium between overground and undergroud plant parts. Jaarboek IBS 1963:31-39.

Denmead OT, Shaw RH. 1962. Availability of soil water to plants as affected by soil moisture conditions and meteorological conditions. Agronomy Journal 54: 385-389.

Doorenbos J, Kassam AH, Bentvelder C, Uittenbogaard G. 1978. Yield response to water. U.N. Economic Commission West Asia, Rome.

Driessen PM. 1986. The water balance of the soil. In: Van Keulen H, Wolf J (Eds). Modelling of agricultural production: weather, soils and crops. Simulation Monographs, Pudoc, Wageningen, 76-116.

Feddes RA, Kowalik PJ, Zaradny H. 1978. Simulation of field water use and crop yield. Simulation Monographs, Pudoc, Wageningen, 195 p.

Gollan T, Passioura JB, Maas R. 1986. Soil water status affects the stomatal conductance of fully turgid wheat and sunflower leaves. Australian Journal of Plant Physiology 13:459-464.

Schulze ED. 1986. Carbon dioxide and water vapor exchange in response to drought in the atmosphere and in the soil. Annual Review of Plant Physiology 37:247-274.

Van Laar HH, Goudriaan J, Van Keulen H. 1997. SUCROS97: Simulation of crop growth for potential and water-limited production situations (as applied to spring wheat). Quantitative Approaches in Systems Analysis, 14. AB-DLO, Wageningen, The Netherlands, 52 pp. plus appendices.

Wang Huaqi, Bouman, BAM., Dule Zhao, Wang Changgui and Moya PF, 2002. Aerobic Rice in Northern China - Opportunities and Challenges. In: Bouman BAM, Hengsdijk H, Hardy B, Bindraban PS, Tuong TP, Ladha JK (Eds). Water-wise Rice Production. Proceedings of the International Workshop on water-wise Rice Production, 8-11 April, 2002, Los Baños,Philippines. Los Baños, (Philippines): International Rice Research Institute, p 143-154.

Yang Xiaoguang, Wang Huaqi,Wang Zhimin, Zhao Junfang, Chen Bin, Bouman BAM. 2002. Yield of aerobic rice (Han Dao) under different water regimes in North China. In: Bouman BAM, Hengsdijk H, Hardy B, Bindraban PS, Tuong TP, Ladha JK (Eds). Water-wise Rice Production. Proceedings of the International Workshop on water-wise Rice Production, 8-11 April, 2002, Los Baños, Philippines. Los Baños, (Philippines): International Rice Research Institute, p 155-164.