Predicting Rice Lodging Risk from the Distribution of Available Nitrogen in Soil Using UAS Images in a Paddy Field.

Rice lodging causes a loss of yield and leads to lower-quality rice. In Japan, Koshihikari is the most popular rice variety, and it has been widely cultivated for many years despite its susceptibility to lodging. Reducing basal fertilizer is recommended when the available nitrogen in soil (SAN) exceeds the optimum level (80-200 mg N kg-1). However, many commercial farmers prefer to simultaneously apply one-shot basal fertilizer at transplant time. This study investigated the relationship between the rice lodging and SAN content by assessing their spatial distributions from unmanned aircraft system (UAS) images in a Koshihikari paddy field where one-shot basal fertilizer was applied. We analyzed the severity of lodging using the canopy height model and spatially clarified a heavily lodged area and a non-lodged area. For the SAN assessment, we selected green and red band pixel digital numbers from multispectral images and developed a SAN estimating equation by regression analysis. The estimated SAN values were rasterized and compiled into a 1 m mesh to create a soil fertility map. The heavily lodged area roughly coincided with the higher SAN area. A negative correlation was observed between the rice inclination angle and the estimated SAN, and rice lodging occurred even within the optimum SAN level. These results show that the amount of one-shot basal fertilizer applied to Koshihikari should be reduced when absorbable nitrogen (SAN + fertilizer nitrogen) exceeds 200 mg N kg-1.

Use of different surface covering materials to enhance removal of radiocaesium in plants and upper soil from orchards in Fukushima prefecture.

The effectiveness of a decontamination methodology whereby herbaceous plants were grown through different materials covering the soil surface followed by subsequent removal of the material, associated plant tissues and attached soil on 137Cs removal from soil was evaluated. Revegetation netting sown with Kentucky bluegrass and white clover had a high effectiveness in 137Cs removal when rolling up the plants, roots, and rhizosphere soil approximately 6 months after sowing. The removal rate was lower when there was higher 137Cs vertical migration down the soil profile. The maximum removal effectiveness of 93.1% was observed by rolling up fertilized Kentucky bluegrass with a well-developed root mat without netting, indicating that applying nutrients to encourage the development of roots or root mats in the 3 cm topsoil rhizosphere is an efficient technology to increase the decontamination effect of plant removal in orchards. Netting and weeding were able to remove up to 80% of 137Cs in the soil without the use of heavy machinery. There was a significant relationship between the removal ratio and the removed soil weight per area. Using the relationship on the site below the canopy, removal of 14.3 kg m-2 DW soil would achieve a removal ratio of 80%. The effectiveness of the technique will decrease with time as radiocaesium migrates down the soil profile but this would be expected to occur slowly in many soils.

Stomatal density of cowpea correlates with carbon isotope discrimination in different phosphorus, water and CO2 environments.

* Stomatal formation is affected by a plant's external environment, with long-distance signaling from mature to young leaves seemingly involved. However, it is still unclear what is responsible for this signal. To address this question, the relationship between carbon isotope discrimination (Delta) and stomatal density was examined in cowpea (Vigna sinensis). * Plants were grown under various environments that combined different amounts of soil phosphorus (P), soil water, and atmospheric CO(2). At harvest, stomatal density was measured in the youngest fully expanded leaf. The (13)C : (12)C ratio was measured in a young leaf to determine the Delta in mature leaves. * Results indicated that stomatal density is affected by P as well as by amounts of water and CO(2). However, stomatal responses to water and CO(2) were complex because of strong interactions with P. This suggests that the responses are relative, depending on some internal factor being affected by each external variable. Despite such complicated responses, a linear correlation was found between stomatal density and Delta across all environments examined. * It is proposed that the Delta value is a good surrogate for the long-term mean of the intercellular (C(i)) to the atmospheric (C(a)) CO(2) concentration ratio (C(i) : C(a)) and may be useful in understanding stomatal formation beyond complicated interactions.

Heterogeneity in spatial P-distribution and foraging capability by Zea mays: effects of patch size and barriers to restrict root proliferation within a patch.

BACKGROUND AND AIMS: Localized proliferation of roots in nutrient-enriched patches seems to be an adaptive response in many plants, but its function is still debatable. To understand the efficiency and limitation of foraging behaviour, the impact of patch size and the presence or absence of a barrier to root proliferation within phosphorus (P)-enriched patches was examined. METHODS: In pots filled with P-poor soil, six treatments of heterogeneous P supply were prepared: three patch sizes with or without a root barrier between patches. In addition, a homogeneous P supply treatment was also prepared. Irrespective of these treatments, each pot received the same total amount of P. Maize (Zea mays) was grown in each pot for 45 d in a greenhouse. KEY RESULTS: P content and biomass were greatest in plants grown in the largest patch due to successful root proliferation, and were higher in the presence of a root barrier. Interestingly, plants preferentially developed adventitious nodal roots projecting from the stem into the P-enriched soil, particularly in the largest patch with a root barrier. Removal of the barrier reduced the P-uptake capacity per unit root surface area or volume in P-enriched patches, revealing that the P-uptake capacity per root can be suppressed even in P-rich soil if other portions on the root axis encounter P-poor conditions. CONCLUSIONS: The results suggest that the efficiency of root morphological plasticity is largely determined by the size of the P-enriched patch. Furthermore, the results imply a novel aspect of P-uptake physiology that roots in heterogeneous P cannot demonstrate their potential capacity, as would be observed in roots encountering P continuously; this effect is probably mediated by an internal root factor.