Analysis of soil moisture variation by forest cover structure in lower western Himalayas, India

Soil moisture affects various hydrological processes, including evapotranspiration, infiltration, and runoff. Forested areas in the lower western Himalaya in India constitute the headwater catchments for many hill streams and have experienced degradation in forest cover due to grazing, deforestation and other human activities. This change in forest cover is likely to alter the soil moisture regime and, consequently, flow regimes in streams. The effect of change in forest cover on soil moisture regimes of this dry region has not been studied through long term field observations. We monitored soil matric potentials in two small watersheds in the lower western Himalaya of India. The watersheds consisted of homogeneous land covers of moderately dense oak forest and moderately degraded mixed oak forest. Observations were recorded at three sites at three depths in each watershed at fortnightly intervals for a period of three years. The soil moisture contents derived from soil potential measurements were analyzed to understand the spatial, temporal and profile variations under the two structures of forest cover. The analysis revealed large variations in soil moisture storage at different sites and depths and also during different seasons in each watershed. Mean soil moisture storage during monsoon, winter and summer seasons was higher under dense forest than under degraded forest. Highest soil moisture content occurred at shallow soil profiles, decreasing with depth in both watersheds. A high positive correlation was found between tree density and soil moisture content. Mean soil moisture content over the entire study period was higher under dense forest than under degraded forest. This indicated a potential for soil water storage under well managed oak forest. Because soil water storage is vital for sustenance of low flows, attention is needed on the management of oak forests in the Himalayan region.

Effects of Grazing Intensity on Soil Water Regime and Flux in Inner Mongolia Grassland,China

In the past few decades, the increase in grazing intensity has led to soil degradation and desertification in Inner Mongolia grassland, China, due to population growth and shift in the socio-economic system. Two sites with different grazing intensities, continuous grazing site （CG） with 1.2 sheep ha-1 year-1 and heavy grazing site （HG） with 2.0 sheep ha-1 year-1, were investigated at the Inner Mongolia Grassland Ecosystem Research Station （43° 37′ 50″ N, 116° 42′ 18″ E） situated in the northern China to i） characterize the temporal distribution of soil water content along soil profile; and ii） quantify the water fluxes as affected by grazing intensity. Soil water content was monitored by time domain refiectometry （TDR） probes. Soil water retention curves were determined by pressure membrane extractor, furthermore processed by RETC （RETention Curve） software. Soil matric potential, plant available water and water flux were calculated using these data. Both sites showed an identical seasonal soil water dynamics within four defined hydraulic periods： i） wetting transition coincided with a dramatic water increase due to snow and frozen soil thawing from March to April; 2） wet summer, rainfall in accordance with plant growth from May to September; 3） drying transition, a decrease of soil water from October to November due to rainfall limit; and 4） dry winter, freezing from December to next February. Heavy grazing largely reduced soil water content by 43%-48% and plant available water by 46%-61% as compared to the CG site. During growing season net water flux was nearly similar between HG （242 mm） and CG （223 mm） sites between 5 and 20 cm depths. However, between 20 and 40 cm depths, the upward flux was more pronounced at HG site than at CG site, indicating that water was depleted by root uptake at HG site but stored at CG site. In semi-arid grassland ecosystem, grazing intensity can affect soil water regime and flux, particularly in the growing season.

EVALUATING QUINOA LODGING RISK AND YIELD UNDER DIFFERENT IRRIGATION THRESHOLDS, NITROGEN RATES AND PLANTING DENSITIES IN NORTH-WESTERN CHINA

Lodging is a major yield-limiting factor of quinoa production.In 2018 and 2019,the orthogonal field experiments were conducted to investigate the responses of quinoa lodging risk and yield to irrigation threshold(soil matric potential of−15,−25 and−55 kPa),nitrogen rate(80,160 and 240 kg·ha^(−1))and planting density(20,30 and 40 plants m^(−2)).Results showed that high irrigation thresholds and nitrogen rates significantly(P<0.05)increased plant height and fresh weight per plant,and high planting densities reduced stem diameter and strength,all of those led to significantly(P<0.05)high lodging risks.The−15 and−55 kPa treatments gave the lowest actual yield(P<0.05)in 2018 and 2019,respectively.Higher lodging rate with a nitrogen rate of 240 kg·ha^(−1) resulted in a lower actual yield than 80 and 160 kg·ha^(−1) in both years.Planting density of 30 plants m^(−2) gave a significantly(P<0.05)greater estimated yield than 20 plants m^(−2) and had a lower lodging rate than 40 plants m^(−2),resulting in the maximum actual yield among planting densities.In conclusion,a moderate irrigation threshold of−25 kPa,a nitrogen rate of 80−160 kg·ha^(−1) and an intermediate planting density of 30 plants m−2 were determined to be best for quinoa cultivation in North-western China.In addition,the lower-stem lodging index(quarter plant height)could evaluate lodging risk more accurately than middle-stem(half plant height)or upper-stem(three quarters plant height)lodging indexes.