Agricultural Water Management 230 (2020) 105979

https://doi.org/10.1016/j.agwat.2019.105979

Published by CAU and ARO:

Jianchu Shi a, Xun Wu b, Xiaoyu Wang a, Mo Zhang a, Le Han a, Wenjing Zhang a, Wen Liu a, Qiang Zuo a,*, Xiaoguang Wu c, Hongfei Zhang c, Alon Ben-Gal d
a College of Land Science and Technology, China Agricultural University, Key Laboratory of Plant-Soil Interactions, Ministry of Education, and Key Laboratory of Arable
Land Conservation (North China), Ministry of Agriculture, Beijing 100193, China
b College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China
c Land Management Center of Inner Mongolia Autonomous Region, Hohhot 010020, China
d Soil, Water and Environmental Sciences, Agricultural Research Organization, Gilat Research Center, Mobile Post Negev 85280, Israel

ABSTRACT

Plant water deficit index (PWDI) represents the extent of water stress by relating soil moisture to the ability of a plant to take up water including consideration of the relative distribution of soil water to roots. However, for a smart irrigation decision support system, we are challenged in determining reliable thresholds of PWDI to initiate irrigation events to achieve predetermined yield and/or water use efficiency (WUE) targets. Taking drip irrigated maize and sprinkler irrigated alfalfa as examples, field experiments were conducted to investigate the
choice and effects of PWDI thresholds. The results indicated that, with increasing PWDI thresholds, irrigation times and quantity of water, as well as crop transpiration, growth, and yield, were all significantly limited while WUE was enhanced except under extremely stressed conditions. To disconnect the unpredictable effects of other factors, yield and WUE were normalized to their corresponding potential values. Within the experimentally determined range of PWDI, relative yield and WUE were described with linear functions for maize, and linear
and quadratic functions for alfalfa, allowing identification of the most efficient threshold value according to the objective parameter of choice. The method described can be adopted in smart irrigation decision support systems with consideration of spatial variability and after further verification and improvement under more complicated situations with various crop types and varieties, environmental conditions, cultivation modes, and wider or dynamic PWDI thresholds allowing regulated deficit irrigation.

Agricultural Water Management 240 (2020) 106293

https://doi.org/10.1016/j.agwat.2020.106293

Publication by CAU and ARO:

Xun Wu a, Qiang Zuo b, Jianchu Shi b,*, Lichun Wang c, Xuzhang Xue c, Alon Ben-Gal d
a College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China
b College of Land Science and Technology, China Agricultural University, Key Laboratory of Plant-Soil Interactions, Ministry of Education, Key Laboratory of Arable Land
Conservation (North China), Ministry of Agriculture, Beijing 100193, China
c National Research Center of Intelligent Equipment for Agriculture, Beijing 100097, China
d Soil, Water and Environmental Sciences, Agricultural Research Organization, Gilat Research Center, mobile post Negev 85280, Israel

ABSTRACT

During wetting-drying cycles, divergence is often found between the immediately improved soil water conditions after re-watering and the recovery of plant water status from stress, which ensues only gradually. Such an apparent hysteresis effect of water stress (HEWS) is usually neglected in simulating root-water-uptake (RWU) by empirical models. To consider HEWS in the empirical macroscopic RWU model of Feddes, a water stress recovery coefficient (δ) was introduced based on two lysimetric experiments under greenhouse and field conditions for
winter wheat. The integrated effects of historical water stress events were investigated by assuming that the normalized influence weight of each past stress event declines with the increase of time interval before simulation as an exponential function of attenuation rate. Although δ could be described by an exponential function of an integrative index representing the general historical stress extent (R2 = 0.65, P < 0.001), with an attenuation rate smaller than 0.13, it is challenging to establish such a function practically. An attenuation rate close to zero means HEWS is mainly dominated by the water stress on the previous day, validated by a significant relationship between the relative transpiration or stomatal conductance on the day after irrigation and the water stress extent on the day before irrigation. Therefore, a simplification, substituting the integrative index in the exponential function with the stress extent on the previous day, was proposed for estimating δ. Compared to the traditional RWU model, the revised model considering HEWS was more successful in simulating relative transpiration and soil water dynamics. Root mean square error of relative transpiration was reduced by 65.9 % and of soil water by 30 % in the greenhouse experiment and by 7.4 % and 12.5 %, respectively, in the field experiment.

Catena 190: 104511 (2020)

Access at: https://digital.csic.es/handle/10261/206694

https://doi.org/10.1016/j.catena.2020.104511

Publication by IAS – CSIC:

Lizardo Reyna-Bowen a,b, Pilar Fernandez-Rebollo b, Jesús Fernández-Habas b, José A. Gómez a

aInstitute for Sustainable Agriculture, IAS, CSIC, Avenida Menéndez Pidal S/N, 14004 Córdoba, Spain

bDepartment of Forestry Engineering, University of Córdoba, University Campus of Rabanales, Madrid-Cádiz Road Km. 396, 14014 Córdoba, Spain

ABSTRACT

This study evaluated the effect on SOC concentration, stock and fractions in a dehesa divided into two areas ofsimilar soil type but different soil management. Thefirst area was a pastured dehesa (P) with young Holm oaks,planted in 1995 (70 trees ha−1, 12 m × 12 m) and, since 2000, grazed by sheep (3 sheep ha−1) with an averageperiod of grazing of six months a year. Prior to this it was managed in the same way as the second adjacent area.The second area was a cropped dehesa (C) with widely spaced mature Holm oak (14 trees in a 12-ha dehesa), onwhich a mixture of vetch and oats was cultivated every three years and tilled with a chisel plough. After 22 yearsboth dehesas showed similar SOC stock distribution amongst areas with different soil management, with ap-proximately 40 t ha−1in the top 100 cm of the soil. The P dehesa only showed higher SOC stock than the Cdehesa on the surface 0–2 cm (5.86 ± 0.56 t ha-1vs3.24 ± 0.37 t ha−1). The influence of the trees, increasingSOC concentration and content when compared to the area outside the canopy projection, was only detectedunder the mature trees in the C dehesa. In the area outside the tree canopy, both systems showed a similardistribution of soil organic carbon among their different fractions, with the unprotected fraction being thedominant one, followed by the physically and chemically protected fractions. In the C dehesa, the mature trees’presence significantly modified the distribution of soil organic carbon in their surroundings, increasing therelevance of the unprotected fraction. The distribution of soil organic carbon in the unprotected and physicallyand chemically protected fractions were strongly correlated to the overall organic carbon concentration in thesoil, indicating the rapid response of these three fractions to management, with the biochemically protectedfraction showing no correlation, suggesting a high resilience to the changes in carbon budget.