Salinity is a significant constraint in crop productivity. Halophytes are highly salt-tolerant plants that grow in saline soils such as seashore, salt lakeshores, and inland salt marshes. Studies on the cultivation of halophytes using saline water irrigation indicated that halophytes could be used for food, feed, oil, biofuels, medicine, and phytoremediation. By elucidating molecular mechanisms in salt tolerance of halophyte, the salt-tolerance of crops may be improved. Establishment of farming methods that utilize high salt-tolerant plants will help increase agricultural production in salinized regions. In this review, we will show examples of usage of halophytes in agricultural production and discuss the potential of halophytes as genetic resources and alternative crops.

Almost all manuals and textbooks for direct seeding of rice (Oryza sativa L.) in well-drained paddy fields in Japan recommend a sowing depth of 2 to 3 cm. This practical sowing depth is empirical and the eco-physiological basis is unknown. We carried out field experiments using sowing machines similar to those used by farmers and the leading variety in Japan, Koshihikari. The correlations between sowing depth and the lengths of coleoptiles, 1st leaves, and 2nd leaf sheaths were significant, irrespective of cumulative temperatures from sowing to sampling. Mesocotyl length was added to the length of these organs and plotted against sowing depth. These plots indicated that the net length of coleoptiles and 1st leaves increased according to the sowing depth up to 4 cm. The net length of these organs fell short of sowing depth when sown deeper than 4 cm, and the number of greening seedlings declined sharply. In suitable temperature and water conditions in artificial climate chambers, the net length of coleoptiles, 1st leaves, and 2nd leaf sheaths fell short of sowing depth if seeds were sown deeper than 5 cm, and seedling establishment declined significantly. These results revealed that the practical sowing depth was determined by the ability of the rice plant to elongate the net length of the coleoptiles and the 1st leaves, that penetrated the covering soil.

The relationship between temperature and solar radiation during the growth period, with the yield and yield components was analyzed. The 5-year average climate and yield data for 1963–1967, 1988–1992 and 2014–2018 in 41 prefectures were taken from data provided by the Japan Meteorological Agency and Ministry of Agriculture, Forestry and Fisheries. Average temperature(T) and average solar radiation(S) from 29 days before heading to heading and that from 1 to 30 days after heading were calculated as T2 and S2, respectively, and T3 and S3, respectively. Among these climate factors, T2 was the most closely related to yield. T2 was negatively correlated with the total spikelet number per area and yield in the comparison of 41 prefectures in every 5-year average. The tendency of increase in yield as temperature decreased in the comparison among prefectures became stronger over the years. This suggests that the negative effect of high temperature on the regional differences of yield increases over the years by the nationwide improvement of cultivation technique and the increase of temperature during the growth period. On the other hand, in each prefecture, the year with high temperature showed higher solar radiation and higher yield. This suggests that the high temperature caused by global warming may not always decrease yield if the solar radiation increases accordingly.

Wheat cultivar “Setokirara” has a high grain yield and a high bread making quality in western Japan. Although the grain yield is increased by heavy application of nitrogen fertilizer, the protein content in grain is often decreased. Nitrogen topdressing at later growth stages increased both the grain yield and the grain nitrogen content. The changes in nitrogen accumulation between vegetative organs and grain during the grain filling period need to be examined to keep the grain yield and grain protein content constantly high. We investigated the effect of topdressing at the spike formation stage (GS31) and that at anthesis (GS65) for “Setokirara”, “Nishinokaori” and “Norin 61” throughout three seasons. Topdressing at the spike formation stage made “Setokirara” accumulate more nitrogen in vegetative organs at anthesis than “Nishinokaori” or “Norin 61”, while grain yield was higher in “Setokirara” than in “Nishinokaori” or “Norin 61”. “Setokirara” showed lower content of grain nitrogen than “Nishinokaori” or “Norin 61” because of less nitrogen absorption from soil after anthesis and higher grain yield. Most of the applied nitrogen was absorbed before anthesis. “Setokirara” needs more nitrogen topdressing at anthesis to achieve higher nitrogen content in grain to increase grain yield.

To establish a labor-saving method of fertilization omitting topdressing at jointing (JS) and full heading (FHS) stage in the wheat cultivar ‘ChikushiW2’ for Chinese noodles, we investigated the nitrogen elution quantity corresponding to each growth period and the effect of controlled availability fertilizer applied at the tillering stage (TS) on the yield and quality. When the coated urea sigmoid type M; 20-day type fertilizer, S20, was buried at TS, the accumulated nitrogen elution quantity reached the standard JS nitrogen quantity from the flag leaf extraction stage (FLES) to the flowering stage. Therefore, we conducted a ¹⁵N-labeled ammonium sulfate experiment at JS and FLES. There were no significant differences in the nitrogen content, fertilized nitrogen utilization rate, yield and quality depending on the time of fertilizer application, as was obtained for the ear number, yield, and grain protein content. This suggested that S20 can be used as fertilizer at JS. The nitrogen elution quantity of S20 from FLES to 24 days after heading stage was slightly smaller than that of topdressing at FHS. However, the combination of fast-acting nitrogen fertilizer and controlled availability fertilizer applied at TS gave a grain protein content rate of more than 12% and almost the same growth and yield as the split dressing. We concluded that one-time topdressing at TS is practical and enough to omit fertilization at JS and FHS.

Plants from six cultivars were pinched between the seventh and eighth nodes at stages V9–V10 or around V14 to examine the effect of pinching on growth and yield. Experiments were conducted under field conditions in 2016 and 2018, respectively. There was no significant difference in the degree of lodging between control and pinched plants. Pod number and seed yield values correlated significantly in these experiments; and, both were lower in the pinched plot than in the control, except for Kotoyutaka. Pinching increased branch pod number in Tamahomare, Fukuibuki and Kotoyutaka plants. However, this increase could not compensate for the decrease in the main-stem pod number of Tamahomare and Fukuibuki plants. In Kotoyutaka, the numbers, branch node and pod per node increased by pinching in low-order nodes; consequently, the pod number per plant was unaffected. These results suggest that the effect of pinching on soybean growth and yield components is cultivar-dependent. Cultivars for which pinching did not reduce yield were considered to have the ability to increase the node and pod per node numbers at low-order nodes.

In barley cultivar “Kirarimochi”, many premature tillers are observed at harvesting while the grain yield and spike number increase with additional topdressing at later growth stages. The amount of nitrogen fertilizer applied was 4 g m^–2 at pre-sowing, 2 g m^–2 at tillering stage, 6 g m^–2 at spike formation stage and 6 g m^–2 at anthesis (4-2-6-6). The appearance of many tillers at the early growth stage might inhibit the late emerging tillers from appearing. The amount of topdressing at the tillering stage was increased and topdressing at the spike formation stage omitted (4-8-0-6) in order to make the tillers productive earlier. Tiller number and spike number were counted by fixed point observation to determine whether the tillers become productive or non-productive. Grain yield, yield components and total weight for 4-8-0-6 were not different from those in 4-2-6-6. The 8 g m^–2 of nitrogen topdressing at the tillering stage, 4-8-0-6, did not increase the number of tillers compared with 2 g m^–2 in 4-2-6-6. Spike number at harvest was twice that at anthesis both in 4-2-6-6 and 4-8-0-6. Many spikes appeared from two weeks after anthesis in 4-8-0-6. The distribution of culm length was bimodal. There were many spikes with a culm length less than 600 mm in 4-2-6-6 and 4-8-0-6.

The productivity of commercial rice cultivation can be improved by efficiently applying fertilizer according to the growth of the rice plant. Remote sensing can be a useful tool to capture the growth of rice plants, but a system to translate this information for application in fertilizer management needs to be developed. This study aims to develop a simple growth model for fertilizer management using sensing information. A simple growth and yield prediction model was developed based on field trials conducted with different soil types and nitrogen management for two years by using a high-yielding cultivar Yumiazusa and Akitakomachi. We developed a simplified growth model to determine the nitrogen fertilization rate. Dry matter weight, nitrogen uptake, and yield were affected by year, soil, and nitrogen fertilizer application in all years. Yumiazusa showed high yields under all conditions, which could be attributed to preferable traits for light interception. A simple growth model based on the relationship between leaf area index (LAI) and nitrogen uptake was developed. Cross-validation showed that the accuracy of the model's prediction was high with a coefficient of determination of 0.98 for dry weight in both years, allowing for accurate predictions of dry matter production based on LAI and nitrogen uptake in different soils, varieties, and years. However, the coefficient of determination of grain yield varied from 0.91 in 2017 to 0.83 in 2018, and the treatment of the harvest index in the model remains an issue.

We compared methods of measuring the normalized difference vegetation index (NDVI) with a handheld NDVI sensor (GreenSeeker Handheld Crop Sensor) in estimating the fraction of light interception of the soybean community. Soybeans were planted at the densities of 2, 5, 10, 15, and 30 plants m⁻² in Yamaguchi Prefecture in 2019. There are two methods of measurement: the wiper method that intersects the ridges and the linear method that measures only the ridges. NDVI was measured nine times from the establishment of seedlings to the seed filling stage. On the same day, the fraction of light interception was measured using a photosynthetic active radiation sensor. Estimation of the fraction of light interception from NDVI showed that the error was smaller in the wiper method than in the linear method. The radiation use efficiency (RUE) was calculated using the fraction of light interception estimated from NDVI, and it was compared with RUE calculated from the measurement value. RUE of the wiper method corresponded with measured RUE, while RUE of the linear method was less than measured RUE for all the planting densities except 2 plants m⁻². These results indicate that the wiper method is more accurate than the linear method when estimating the fraction of light interception from NDVI measured with a handheld NDVI sensor in soybean communities.

Non-coated rice seeds were directly seeded with a puddling seeder and snowmelt water in Akita prefecture, a heavy snow-fall region in Japan, to expediate the early limits of seeding. The dry seeds of ”Moeminori” were sown using snowmelt water in late March to early April in 2014 to 2017 (snowmelt water seeding, SW). Pre-germinated seeds were sown in late April (early seeding, ES) and mid-May (ordinary seeding, OS). In SW, coated urea fertilizer was applied as basal nitrogen fertilizer and the total amount of nitrogen fertilizer was greater than that in OS, except in 2014. The percentage of seedling establishment in SW was similar to that in ES and less than that in OS. The number of seedlings per square meter was higher in SW, because the seeding rate in SW was higher than that in ES and OS. In SW, heading date and maturity date were 4 days and 5 days earlier, respectively, than those in OS. The yield in SW tended to be higher than that in OS. These results suggest that SW using a lodging-tolerant cultivar can produce seedling number and yield equal to those in OS when the basal nitrogen fertilizer is coated urea fertilizer, and the fertilization amount and seeding rate are higher than those of OS; therefore, SW can be of practical use.