The potential of fragipans in sustaining pearl millet during drought periods in north-central Namibia

Sandy soils with fragipans are usually considered poorly suited for agriculture. However, these soils are cultivated in Namibia as they can secure a minimum harvest during droughts. In order to understand the hydrological influence of fragipans in these soils, Ehenge, their soil moisture content was measured for 4 months. These data were then compared to a deep soil without fragipan, Omutunda, which is more productive during normal years but less productive during droughts. The results illustrate that the combination of sandy topsoil and shallow fragipan has beneficial effects on plant-available water during dry periods. Three reasons can be determined: (i) high infiltration rate in the sandy topsoil, (ii) prevention of deep drainage by the fragipan, and (iii) limitation of evaporation losses through the sand. Consequently, transferring these findings to other dry, sandy areas with fragipans, with respective consequences on farming practices, crop productivity, and food security, should be possible.

TERENGGANU SOIL SERIES TEXTURAL CLASSIFICATION AND ITS IMPLICATION ON WATER CONSERVATION

The updated Terengganu soil series has been made known to the public in 2018 by the Department of Agriculture, Malaysia. One of the most important physical aspects not quantify is the parameter relating to soil’s ability to contain water and allow water infiltration. This information is necessary to help farmers to know the soil suitability characteristics. In the current study, we retrieve the soil particle size of the soil series for further investigation. A pedotransfer function was used to estimate the soil water retention. The properties were then used to estimate the field capacity (FC), permanent wilting point (PWP), and the plant available water (PAW). In this study, we found twelve soil series in Terengganu state. The soil series were categorized into clay, sand, loamy sand, silty clay loam, and clay loam. Batu Hitam, Tasik, Lubok Kiat, Kampong Pusu, Tok Yong, Jerangau, and Tersat Series were found as clay soil. Jambu and Rhu Tapai Series as sand soil. Rudua, Gondang, and Kuala Brang Series corresponded to clay loam, silty clay loam, and loamy sand. Among the soil series, Gondang Series appeared to be the most preferred soil for plantation due to its ability to give the highest plant available water, a lower water infiltration duration than clay, and it required lesser water for irrigation than the clay soil.

Water Infiltration into Sand, Silt, and Clay at Field Capacity

Field capacity (FC), permanent wilting (PWP), and plant available water (PAW) are essential parameters to estimate for soils because they are essential for water irrigation management. However, these parameters were reported in water volume per unit soil volume. Knowing the soil required water volume does not imply immediate water availability, that is, the speed at which the water could be supplied to the soil. This is because there is a lag time between water irrigation initiation and the water increment in the soil depth. This study uses the field capacity’s soil water content to simulate the water infiltration using Richards’ equation. The studied soil medium was silt, sand, and clay. The study allows an estimate of water infiltration time and infiltrated water to relate to the soil depth of interest. The clayey has the highest FC, and the silty soil has the highest PAW. The results revealed silty soil could contain more readily water for plant growth than sand and clay. This study also revealed silty soil to be a better soil medium than sand and clay. It has the best tradeoff between water infiltration time and the infiltrated amount of water for plant absorption. This study’s coupling technique will be a useful tool for farmers and field practitioners to assess any site based on the soil texture at an early stage of water irrigation investigation.

Soil Moisture as Predictor of Plant Water Status

Soil water potential can be used as a proxy for plant available water in irrigation scheduling. This study investigated the relationship between soil water potential and plant water status of pines (Pinus sylvestris L.) planted into two different substrates. Predawn leaf water potential as a well-established measure of the plant water status and soil water potential correlated very well. However, estimating the plant water status from individual sensor readings is subject to significant estimation errors. Furthermore, it was shown that heterogeneous soil/root ball combinations can lead to critical effects on the soil water balance, and that sensors installed outside of the root balls cannot estimate the plant water status without site-specific calibration.

Effect of different types of soil tillage for sunflower on some soil physical characteristics. Part I: soil moisture

The investigation was carried out during 2014–2016 in the land of General Toshevo town in the South Dobrudzha region on slightly leached chernozem soil type. The effect of the types of soil tillage for sunflower given bellow was followed: ploughing at 24–26 cm, chisel-plough at 24–26 cm, disking with disk harrow at 10–12 cm and direct sowing (no-tillage) on the soil moisture content. Based on bulk density, wilting point and the determined soil moisture content the plant-available water was calculated. The additional soil tilths of the areas subjected to ploughing, chisel-ploughing and disking with disc harrow included double spring pre-sowing cultivation with harrowing. To destroy the emerging weeds in the variant with direct sowing, a total herbicide was applied. The soil moisture content was evaluated during three main stages of sunflower development: emergence, flowering and technical maturity. The investigated parameter was determined for each of the studied layers – 0–10, 10–20, 20–30, 30–40 and 40–60 cm. In years with normal amounts of rainfalls, no significant differences in the soil moisture under the different ways of soil tillage were observed. Conventional ploughing and tillage without turning of the soil layer contributed to accumulation of more moisture and to higher moisture storage down the soil profile under heavy and intensive rainfalls. Tillage without turning of the soil layer, minimal and no tillage maintained more and better soil moisture in years with limited precipitation and in periods of drought.

Pulse Root Ideotype for Water Stress in Temperate Cropping System

Pulses are a key component of crop production systems in Southern Australia due to their rotational benefits and potential profit margins. However, cultivation in temperate cropping systems such as that of Southern Australia is limited by low soil water availability and subsoil constraints. This limitation of soil water is compounded by the irregular rainfall, resulting in the absence of plant available water at depth. An increase in the productivity of key pulses and expansion into environments and soil types traditionally considered marginal for their growth will require improved use of the limited soil water and adaptation to sub soil constrains. Roots serve as the interface between soil constraints and the whole plant. Changes in root system architecture (RSA) can be utilised as an adaptive strategy in achieving yield potential under limited rainfall, heterogenous distribution of resources and other soil-based constraints. The existing literature has identified a “‘Steep, Deep and Cheap” root ideotype as a preferred RSA. However, this idiotype is not efficient in a temperate system where plant available water is limited at depth. In addition, this root ideotype and other root architectural studies have focused on cereal crops, which have different structures and growth patterns to pulses due to their monocotyledonous nature and determinant growth habit. The paucity of pulse-specific root architectural studies warrants further investigations into pulse RSA, which should be combined with an examination of the existing variability of known genetic traits so as to develop strategies to alleviate production constraints through either tolerance or avoidance mechanisms. This review proposes a new model of root system architecture of “Wide, Shallow and Fine” roots based on pulse roots in temperate cropping systems. The proposed ideotype has, in addition to other root traits, a root density concentrated in the upper soil layers to capture in-season rainfall before it is lost due to evaporation. The review highlights the potential to achieve this in key pulse crops including chickpea, lentil, faba bean, field pea and lupin. Where possible, comparisons to determinate crops such as cereals have also been made. The review identifies the key root traits that have shown a degree of adaptation via tolerance or avoidance to water stress and documents the current known variability that exists in and amongst pulse crops setting priorities for future research.

On the role of parent material for predictive mapping of soil properties in mountain forests

<p>Parent material is widely recognised as an important factor for soil formation. Thus, quantitative information on the lithogenetic, geochemical, and physical characteristics of the subsolum geological substrates (SSGS) are essential input parameters for digital soil mapping (DSM). Forming the interface between bedrock – the domain of geologists, and soil – the domain of soil scientists, spatial information on SSGS is however scarce. Recognising these shortcomings, a novel geochemical-physical classification system for subsolum geological substrates has been developed, in order to support DSM at a regional scale. The units of the classification system reflect the properties of the SSGS also considering multilayering structure of quaternary deposits. The basis for the classification are mineral component groups, namely dolomite, calcite, and felsic, mafic, and clay minerals. In order to test the relevance of SSGS for the prediction of spatially continuous physical and chemical soil properties, Generalized Additive Models (GAMs) were applied to the forested area of Tyrol, Austria. The plant-available water storage capacity, as a physical soil property, was predicted with r² = 0.56. The Ellenberg´s mean soil reaction indicator value for vegetation turned out to be a suitable proxy for soil pH value and was predicted with r² = 0.75. Topography and associated morphometric terrain features are formative characteristics of mountain areas and, due to its various effects on redistribution processes as well as on water and energy budget of forest sites, are considered as the most essential soil forming factors. Thus, variables derived from digital terrain models, which are available in high spatial resolution, are assumed to be one of the most important predictors for digital soil mapping. In our study we could show however, that SSGS information is the most relevant predictor for both investigated soil properties. In the plant-available water storage capacity model, the predictor variables related to SSGS account for around 76% of the variance explained. Accordingly, a special focus should be placed on the predictive relevance of parent material and the frequently unlocked potential of quantitative geological substrate information. Thus, the newly developed subsolum geological substrate information could stimulate further developments in digital soil mapping, especially in mountain environments.</p>