Yoshihito Sunaga

Variations in Nitrogen Uptake and Nitrate-Nitrogen Concentration among Sorghum Groups

Abstract Nitrogen uptake and nitrate-N concentration in forage sorghums, which are related to ground water pollution or feed quality under conditions of crop fertilization by only animal wastes, were examined. Seventy-four genotypes of sorghum and Sudan grass were tested. They were classified into 4 groups; grain type and dual purpose type sorghums (6 and 13 genotypes, respectively, Sorghum bicolor Moench), sorgo type sorghum (21, S. bicolor), Sudan type sorghum (22, S. bicolor × S. sudanense (Piper) Stapf), Sudan grass (12, S. sudanense). There was a strong correlation between dry matter (DM) yield and N uptake, with the sorgo type producing the highest DM matter yield and showing the highest N uptake. Nitrate-N, which causes nitrate poisoning of ruminants, was detected mostly in the stem of all the genotypes. The nitrate-N concentration based on DM could be calculated accurately by multiplying the nitrate-N concentration of stem on a fresh matter basis by the DM partitioning ratio of stem divided by the DM concentration of stem. The grain type and the dual purpose type of sorghums with dry stem showed the lowest nitrate-N concentration because these plants had a lower DM partitioning ratio of stem and higher DM concentration of stem. Sudan grass and Sudan type sorghum with the genetic background of Sudan grass showed higher nitrate-N concentrations owing to their ability to accumulate nitrate-N.

Transfer factor of radioactive cesium to forage corn (Zea mays L.) from soil to which contaminated farmyard manure had been applied

Abstract Radioactive cesium (Cs) deposited after the Fukushima Daiichi Nuclear Power Station accident contaminated farmyard manure (FYM) in the wide area surrounding the plant. We conducted a field trial to determine the transfer factor of radioactive Cs to forage corn (Zea mays L.) from soil to which the contaminated FYM had been applied. The main purpose of this experiment was to examine the behavior of the radioactive Cs from contaminated FYM that was incorporated in agricultural fields. Application of FYM containing 3900 Bq kg−1 dry matter (DM) of cesium-137 (137Cs) at a rate of 4.3 kg m−2 increased the 137Cs concentration in the soil by 64 Bq kg−1 dry soil, and in the forage corn by 9.2 Bq kg−1 DM. Therefore, we calculated the transfer factor to corn plants from the soil after application of contaminated FYM to be 0.14. This value is lower than that observed for soil to which uncontaminated FYM had been applied as a control, and it is within the range of reported soil-to-plant transfer factors of 0.003–0.49 listed in the recent parameter handbook by International Atomic Energy Agency. The increase in the radioactive Cs concentration in the corn plants, expressed as the sum of 137Cs and cesium-134 (134Cs), was only 3% of the 2012 provisional tolerance level for cattle roughage in Japan. Even though the application of contaminated FYM did not cause a large change in the radioactive Cs concentration in the corn plants in this trial, such application should be carefully controlled because it increased radioactive Cs concentrations in both soil and forage corn.

Weathering half-life of radioactive cesium for winter rye (Secale cereale L.) and Italian ryegrass (Lolium multiflorum Lam.) directly contaminated by the 2011 Fukushima Daiichi Nuclear Power Station accident

Abstract Changes in radioactive cesium (radiocesium) concentrations in winter rye (Secale cereale L.) and Italian ryegrass (Lolium multiflorum Lam.) grown in fields contaminated by the accident at the Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company were examined to clarify the half-lives of weathering as an environmental process that removed radiocesium during the early stages after its deposition. The radiocesium concentrations in the rye plants that resulted from direct deposition of fallout in 2011 decreased greatly from 140.5 kBq kg–1 dry weight (DW) on March 31 to 13.2 kBq kg–1 DW on April 27, during the 27 d between the vegetative growth and heading stages. The amounts of rye radiocesium per unit area decreased simultaneously, from 69.8 kBq m–2 to 12.6 kBq m–2. The radiocesium concentrations in rye were half and a quarter of those in Italian ryegrass during the vegetative and heading stages, respectively, although the radiocesium concentrations in Italian ryegrass also decreased with plant growth. The values of the weathering half-life of 8.0 and 11.0 d for the radiocesium concentration per unit DW and amount per unit area in rye were approximately half those of Italian ryegrass, at 14.1 and 23.1 d, respectively. Therefore, less radiocesium-contaminated material seemed to be retained on the plant surface of rye than on Italian ryegrass. The radiocesium concentrations of rye harvested in the same experimental fields in the year following the accident were below the value defined in the February 2012 provisional regulation for cattle roughage (100 Bq kg–1 at a water content of 0.8 kg kg–1).

Management of nitrogen fertilizer application rates based on soil nitrogen fertility with the goal of lowering nitrate nitrogen concentrations in Sudangrass (Sorghum sudanense (Piper) Stapf)

Abstract High levels of nitrate nitrogen (NO3-N) in forage crops can poison ruminants. To promote stable production of Sudangrass (Sorghum sudanense (Piper) Stapf) with safe NO3-N levels, we investigated the influence of soil nitrogen (N) on Sudangrass yield and on NO3-N concentrations, and we propose a fertilizer management strategy based on soil N levels for a regime based on the application of cattle manure composted with sawdust. We used the available N content determined by incubation of fresh soil as an indicator of soil N. Both the yield and NO3-N concentration of Sudangrass increased with increasing available N. The NO3-N concentrations in the first grass harvest remained lower than 2 g kg−1 (dry-matter basis), which represents the critical level to avoid nitrate poisoning of ruminants in Japan, with an available N content of 40 mg kg−1 (dry-soil basis), the level where yield remained approximately stable without additional N fertilizer. The NO3-N concentration increased linearly with increasing available N and exceeded the critical level when available N exceeded 50 mg kg−1. Under low levels of N (less than 30 mg kg−1), the target yields for the first grass harvest, with safe levels of NO3-N, could be obtained with the application of 10 g N m−2 in fertilizer, lower than the recommended rate of 15 g N m−2. The NO3-N concentration was higher in the second grass harvest under the same levels of soil N with an available N of 40 mg kg−1 or more. The NO3-N concentrations in the second harvest exceeded the critical level when the available N was 40 mg kg−1. These results indicate that available N content is an effective indicator for the stable production of Sudangrass with acceptably low NO3-N concentrations.

A simple method for estimating the nitrate nitrogen concentration based on dry matter in standing sorghum (Sorghum bicolor Moench) using stem juice test and dry matter content

Abstract A simple method was developed for estimating the nitrate nitrogen (NO3-N) concentration in standing sorghum (Sorghum bicolor Moench) crop at maturity. In the method, the concentration of NO3-N in whole plants on a dry matter basis can be accurately estimated by multiplying the concentration factor (CF, NO3-N concentration of stern on a fresh matter basis) by the dilution factor (DF, dry matter partitioning ratio of stern divided by the dry matter content of stern or fresh matter weight of stern divided by the dry matter weight of whole plant). CF was linearly correlated with the NO3-N concentration in stern juice squeezed from stern discs with a thickness of 1 cm obtained by cutting horizontally at a location corresponding to a ratio of 25% to the total stern length. CF can be estimated by multiplying the NO3-N concentration in stern juice by a factor of 0.68 or 0.53 for grain and dual purpose types or sorgo type, respectively. The values of the coefficients of determination (R 2) of the linear regression were above 0.7. When DF was plotted with the dry matter content of whole plants (DM%), regression curves were obtained for both sorghum types with R 2 > 0.8. The equations were as follows: DF= 0.00721X 2-0.503X + 10.72 for grain and dual purpose types, DF=0.00445X 2 -0.337X + 8.86 for sorgo type, where X is DM%. The NO3-N concentrations estimated by multiplying CF by DF enabled to predict the measured NO3-N concentrations with an R 2 of 0.873.

Cesium-137 concentration of forage corn and Italian ryegrass in a double cropping system under different rates of cattle farmyard manure application after the Fukushima Daiichi Nuclear Power Station accident in 2011

Abstract Radioactive 137Cs concentrations of forage corn (Zea mays L.) and Italian ryegrass (Lolium multiflorum Lam.) in a double cropping system under continuous cattle farmyard manure (FYM) application were observed for more than 2 years after the Fukushima Daiichi Nuclear Power Station accident in 2011. The experiment field is located 110 km southwest of the Fukushima Daiichi Nuclear Power Station, and the soil contains 137Cs of 920 Bq kg−1 on average. For crop cultivation, nitrogen fertilizer was applied in addition to FYM. The 137Cs concentrations in corn decreased significantly between 2011 and 2012, but only differed significantly between 2012 and 2013 for the plot with no FYM application. For Italian ryegrass, no significant differences were observed between the harvest in 2012 and 2013 despite the FYM application rate. To minimize corn 137Cs concentrations, the FYM application rate should be more than and equal to 30 Mg ha−1 when FYM is used as the major nutrient source. Exchangeable potassium oxide (K2O) greater than around 0.3 g kg−1 was mostly maintained with the FYM application rates. Corn 137Cs concentration appeared to increase at exchangeable K2O levels below 0.15 g kg−1. These results suggest that continuous FYM application can maintain soil nutrients including K2O and thereby control radioactive Cs transfer from the soil. FYM application rate of 30 Mg ha−1 is within the levels recommended by the prefectural governments around Fukushima Prefecture for crop production before the accident. These levels are sufficient to decrease the radioactive Cs concentrations for corn. However, unlike corn, differences in soil chemical properties by FYM application did not affect 137Cs concentrations in Italian ryegrass in this study, although low exchangeable K2O seemed to increase concentrations of stable 133Cs. Further experiments should be conducted to understand the observed differences between corn and Italian ryegrass.

Potassium fertilization and soil diagnostic criteria for forage corn (Zea mays L.) production contributing to lower potassium input in regional fertilizer recommendation

Abstract Effective soil diagnostic criteria for exchangeable potassium (Ex-K) combined with inorganic potassium (K) application rates were developed to lower K input in forage corn (Zea mays L.) production using experimental fields with different application rates and histories of cattle manure compost. Two corn varieties, ‘Cecilia’ as a low K uptake variety and ‘Yumechikara’ as a high K uptake variety, were selected from among 20 varieties and tested to make diagnostic criteria for K fertilization applicable to varieties with different K uptakes. The K uptakes increased from 96 to 303 kg K ha−1 for ‘Cecilia’ and from 123 to 411 kg K ha−1 for ‘Yumechikara’ with increasing Ex-K content on a dry soil basis from 0.11 to 0.92 g kg−1 with no inorganic K fertilizer application. The K uptake by corn for achieving the target dry matter yield of 18 Mg ha−1 was estimated to be approximately 200 kg K ha−1 in common between the two varieties. Yields of both varieties achieved the target yield at an Ex-K content of approximately 0.30 g kg−1 with no K fertilization, although ‘Yumechikara’ reached the target yield at a lower Ex-K content. At the low Ex-K content of 0.1 g kg−1, inorganic K fertilizer application at 83 kg K ha−1 was needed to gain the target yield, and apparent K recovery rate for K fertilizer was calculated to be 70% for both varieties. The K uptakes for gaining the target yield by the K fertilization were lower than that by soil K supply. Based on these results, diagnostic criteria of Ex-K and inorganic K application rates were set up as follows: at an Ex-K content of < 0.15 g kg−1, inorganic K fertilizer is applied at 83 kg K ha−1 (100 kg ha−1 as potassium oxide (K2O) equivalent); at an Ex-K content of 0.15–0.30 g kg−1, the application rate is reduced to 33 kg K ha−1 (40 kg K2O ha−1); at an Ex-K content of ≥ 0.30 g kg−1, inorganic K fertilizer is not applied because of sufficient K in the soil. Additionally, we propose that cattle manure compost be used to supplement soil K fertility.