Morihiro Maeda

Nitrate leaching in an Andisol treated with different types of fertilizers.

Nitrate (NO3) leaching was studied in an Andisol treated with four N fertilizers (SC: swine compost, CU: coated urea, AN: ammonium N, or NF: no fertilizer) for 7 years. Sweet corn (Zea mays L.) was grown in summer, followed by Chinese cabbage (Brassica rapa L. var. amplexicaulis) or cabbage (Brassica oleracea L. var. capitata) in autumn each year. In chemical fertilizer plots treated with AN or CU, NO(3)-N concentrations in soil water at 1-m depth increased markedly in the summer of the second year and fluctuated between 30 and 60 mg l(-1). In the SC plot, NO(3)-N concentration started increasing in the fourth year, reaching the same level as in the AN and CU plots in the late period of the experiment. In the NF plot, NO(3)-N concentration was about 10 mg l(-1) for the first 4 years and decreased to 5 mg l(-1). The potential NO(3)-N concentrations by an N and water balance equation satisfactorily predicted NO(3)-N concentration in the AN and CU plots, but substantially overestimated that in the SC plot, presumably because a large portion of N from SC first accumulated in soil in the organic form. Our results indicate that, under the Japanese climate (Asian monsoon), excessive N from chemical fertilizers applied to Andisols can cause substantial NO3 leaching, while compost application is promising to establish high yields and low N leaching during a few years but would cause the same level of NO3 leaching as in chemically fertilized plots over longer periods.

Water-use efficiency and carbon isotope discrimination in two cultivars of upland rice during different developmental stages under three water regimes

AbstractA pot experiment was conducted in a glasshouse to clarify and quantify the effect of plant part, water regime, growth period, and cultivar on carbon isotope discrimination (CID), and to analyze the relationship between CID, stomatal behavior and water-use efficiency (WUE). The experiment was comprised of two upland rice (Oryza sativa L.) cultivars and three water regimes (100, 70, and 40% of saturation moisture) in a completely randomized design. Plants were harvested at tillering, flowering, and maturity. No significant cultivar differences in above-ground dry matter-based WUE (WUEA) and total dry matter-based WUE (WUET) were observed. WUEA (and WUET) increased with water stress up to tillering, but decreased with water stress after tillering. Significant cultivar differences in CID in all the analyzed plant parts were observed at all harvest times. Reduction in CID with water stress was greatest at tillering, and the effect was less pronounced at flowering and at maturity. At each harvest, the effect was most pronounced in newly developed plant parts. Root and grain tended to have the lowest CID values, and stem the highest, at all harvest times. A negative relationship was observed between CID measured at tillering and WUEA (and WUET) measured over the period from seedling to tillering, whereas a reverse relationship was obtained between CID measured at flowering and WUEA (and WUET) measured over the period from tillering to flowering, and an unclear relationship between CID measured at maturity and WUEA (and WUET) measured over the period from flowering to maturity. The ratio of the intercellular and atmospheric concentration of CO2 (Ci/Ca) were closely associated with CID throughout the water regimes when one cultivar was considered, however, cultivar differences in CID were not related to variations in Ci/Ca. The results indicate that significant cultivar difference existed in CID in all the analyzed plant parts at all harvest times, while corresponding difference in WUEA (and WUET) between the cultivars was not necessarily consistent. Abbreviations: WUE – water-use efficiency; WUEi – instantaneous WUE (or leaf transpiration efficiency); ADM – above-ground dry matter; TDM – total dry matter; WUEA– ADM-based WUE; WUET– TDM-based WUE} CID – carbon isotope discrimination; NL – the newest leaves; FEL – recently fully expanded leaves; FL – flag leaves; P – photosynthesis rate; g – leaf stomatal conductance to water vapor; Ci– intercellular CO2 concentration; Ca– atmospheric CO2 concentration; T – transpiration rate; gs – total conductance of CO2

Nutrient recovery from biomass cultivated as catch crop for removing accumulated fertilizer in farm soil

As a result of long-term continuous use of fertilizers in farm land, a large amount of nutrients accumulate in the soil, increasing the risk of eutrophication or nitrate pollution of groundwater. For rehabilitating the farm soil and recovering nutrients such as nitrogen, phosphorus and potassium, a new system has been developed by our research group. This paper discusses the methodology of extracting nutrients from biomass in order to recover phosphorus and other nutrients in crystal form. Around 80% or higher extraction rates were achieved for phosphorus and potassium by soaking the powdered tissue in distilled water or 1% NaOH solution for 24 h. The extracted phosphorus and potassium act as a potential resource for recycled fertilizer or other industrial materials.

Comparison of simultaneous and separate processes: saccharification and thermophilic L-lactate fermentation of catch crop and aquatic plant biomass.

Catch crop candidates (corn, guinea grass) for recovering nutrients from farm soil and aquatic plants (water caltrop, water hyacinth) were utilized to produce l-lactic acid. The efficiencies of pre-treatment methods for enzymatic saccharification and l-lactate production of two fermentation processes, thermophilic simultaneous saccharification and fermentation (SSF), as well as separate saccharification and fermentation, were compared. Conditions were set at 55°C and pH 5.5 for non-sterile fermentation. Alkaline/peroxide pre-treatment proved the most effective for saccharification in pre-treated corn, guinea grass, water caltrop and water hyacinth with glucose yields of 0.23, 0.20, 0.11 and 0.14 g/g-dry native biomass (24-hour incubation period), respectively. Examination of the two types of thermophilic l-lactate fermentation employed following alkaline/peroxide pre-treatment and saccharification demonstrated that the l-lactate yield obtained using SSF (0.15 g/g in the case of corn) was lower than that obtained using separate saccharification and fermentation (0.28 g/g in the case of corn). The lower yield obtained from SSF is likely to have resulted from the saccharification conditions used in the present study, as the possibility of cellulase deactivation during SSF by thermophilic l-lactate producing bacteria existed. A cellulase that retains high activity levels under non-sterile conditions and a l-lactate producer without cellulose hydrolysis activity would be required in order for SSF to serve as an effective method of l-lactate production.

Groundwater-induced emissions of nitrous oxide through the soil surface and from subsurface drainage in an Andosol upland field: A monolith lysimeter study

Nitrous oxide (N2O) produced in shallow groundwater has two emission pathways to the atmosphere: dissolution in subsurface drainage and groundwater and later degassing from water surfaces open to the atmosphere, and upward gas diffusion. N2O undergoing upward diffusion through the soil surface cannot usually be distinguished from N2O produced in the topsoil. To evaluate the emission pathway and rate of groundwater-induced N2O, we conducted a one-year experiment using monolith lysimeters containing 1 m-long undisturbed Andosol. We measured emission of N2O via the soil surface and dissolved N2O emitted via subsurface drainage from the non-planted lysimeters under two conditions without fertilizer-nitrogen (N) addition: (1) with the groundwater table at 0.9 m depth (GW), and (2) without any groundwater table (nonGW). Total soil surface N2O emissions in the GW and nonGW treatments were 21.0 ± 6.3 and 17.0 ± 1.1 mg N m–2 yr–1, respectively (mean ± standard error, n = 3), and the difference between the two treatments was not significant. Total dissolved N2O emissions via drainage in the GW and nonGW treatments were 11.40 ± 5.68 and 0.42 ± 0.03 mg N m–2 yr–1, respectively. The presence of groundwater significantly increased dissolved N2O emission under zero fertilizer-N addition. This is due to the one to three orders of magnitude higher concentration of dissolved N2O in the GW treatment. Our results indicate that the presence of groundwater increases total N2O emissions from an Andosol upland field via these two pathways.

Seasonal changes in the performance of a catch crop for mitigating diffuse agricultural pollution

An in situ technology for mitigating diffuse agricultural pollution using catch crops was developed for simultaneously preventing nitrate groundwater pollution, reducing nitrous oxide (N2O) gas emissions, and removing salts from the topsoil. Seasonal changes in the performance of a catch crop were investigated using lysimeters in a full-scale greenhouse experiment with 50 d cultivation of dent corn. Catch crop cultivation significantly reduced the leached mineral nitrogen by 89-91% in summer, 87-89% in spring, and 61-82% in winter, and it also significantly reduced the N2O emission by 68-84% in summer. The amounts of nitrogen uptake by the catch crop were remarkably higher than those of leached nitrogen and N2O emission in each season. Catch crop cultivation is a promising technology for mitigating diffuse agricultural pollution.

Natural ^15N and ^13C Abundance in Andisols Influenced by Long-Term Fertilization Management in Japan

Abstract Two field experiments were conducted on Andisols in Japan to evaluate the changes in the natural 15N and 13C abundance in the soil profile and to determine whether the values of δ15N could be used as an indicator of fertilizer sources or fertilizer fate. The 6-year experiment conducted at the National Agricultural Research Center (NARC) consisted of the following treatments: application of swine compost (COMPOST), slow-release nitrogen fertilizer (SRNF), readily available nitrogen fertilizer (RANF), and absence of fertilization (CONTROL). Experimental plots located at the Nippon Agricultural Research Institute (NARI) received cattle compost at different rates for 12 years; a forest soil at this site was sampled for comparison. Swine compost application led to a considerable change in the δ15N distribution pattern in the soil profile, with the highest δ15N values recorded in the top 20 cm layers of the COMPOST plot, decreasing in the sequence of CONTROL >- RANF > SRNF, mainly due to the relatively high δ15N value of swine compost and its subsequent decomposition. In contrast, SRNF application resulted in the lowest δ15N values in soil, indicating the presence of negligible nitrogen losses relative to input and low nitrogen cycling rates. Values of δ15N increased with compost application rates at NARI. In the leachate collected at 1-m depth, the δ15N values decreased in the sequence of COMPOST > RANF ≥ CONTROL > SRNF. The δ13C values in soil peaked in the 40–60 cm layers for all the fertilizers. The δ13C value was lowest in forest soil due to the presence of plant residues in soil organic matter. These results indicated that the δ15N values in the upper soil layers or leachate may enable to detect pollution sources of organic or inorganic nitrogen qualitatively in Andisols.

Characteristics of Nutrient Salt Uptake Associated with Water Use of Corn as a Catch Crop at Different Plant Densities in a Greenhouse

Abstract Dent corn, as a catch crop used for salt removal, was cultivated at different densities, i.e ., 7.3 (low density), 59.7 (normal density), and 119.5 plants m −2 (high density), during a 50 d fallow period after cultivation of a commercial crop in a greenhouse, to analyze the characteristics of nutrient salt (N, K, Mg, and Ca) uptake by roots and to study the effect of plant density on the characteristics associated with crop water use. Leaf area index for the high and normal density treatments reached extremely high values of 24.3 and 14.9, respectively. These values induced higher transpiration rates that were estimated using the Penman-Monteith model with the incorporation of specific parameters for crop and greenhouse conditions. The total N, K, Mg, and Ca contents in the crop canopy at harvest were 26.8, 13.0, 1.0, and 1.7 g m −2 , respectively, under the high density treatment. The dynamics of salt uptake rates for high, normal, and low density treatments were evaluated by assessing weekly changes in salt content, and were subsequently compared against the transpiration rate. A positive linear relationship was obtained between these 2 parameters for all 3 density treatments and all tested salts. Hence, higher transpiration rates caused higher salt uptake rates through water absorption. On the other hand, salt uptake efficiency per unit water use by cultivation was lower in the low density treatment. Therefore, management procedures with dense planting that induce higher transpiration rates and lower evaporation rate are extremely important for the effective cultivation of corn catch crops.

Advantages of pre-harvest temporal flooding in a catch crop field in relation to soil moisture and nutrient salt removal by root uptake

Catch crop cultivation coupled with subsequent flood activity is an environmental friendly method of removing nutrient salts from soil in greenhouse. However, in comparison with the usual fallow period in greenhouse horticulture in Japan, a longer time is required for cultivation and soil drying after flooding. To minimize such time while retaining catch crop performance, temporal flooding was conducted in an experimental catch crop field of corn before harvest (i.e., pre-harvest temporal flooding), when crops were growing well and most nutrient salts within the soil had been taken up by the roots. Results showed that pre-harvest temporal flooding enhanced crop growth and stomatal opening; hence, evapotranspiration (mostly transpiration) was increased to a high value (3.5 times that of bare soil plot in greenhouse). Therefore, compared with the bare soil field, there was a remarkable pronounced decrease in the soil water content due to evapotranspirational water loss in the catch crop field after temporal flooding. Furthermore, the total nutrient (nitrogen) uptake by crops was also significantly accelerated in relation to pre-harvest flooding owing to the increase in crop growth. It was also found that electrical conductivity and nitrate nitrogen concentration of soil solution (at a soil-water ratio of 1:5) decreased with time owing to root uptake, and were at a fairly low level when pre-harvest flooding was conducted. These results suggest that pre-harvest temporal flooding shortens the implementation time by accelerating soil drying, and increases salt removal by root uptake; thus, this method delivers considerable advantages for practical use in catch crop cultivation.

Water collection efficiency of wick samplers under steady state flow conditions

Abstract Wick samplers could be used for measurements of solute transport. Water collection efficiency of wick samplers, defined as the volume of water collected by a sampler divided by the water flux from the root zone, should be close to 100%. We used three wick samplers differing in wall height in Hydric Hapludands under constant rainfall intensity and examined the effects of the rainfall intensity and wall height on the water collection efficiency based on experimental data and a numerical analysis. The water collection efficiency of wick samplers increased with the rainfall intensity and wall height because the increase in both rainfall intensity and wall height resulted in a distribution of the total potential inside the wick sampler close to that outside the wick sampler. Furthermore, the ratio of the cross-sectional area of the drain hole to that of the cylinder must be taken into account in the design of a wick sampler.