Heat stress is one of the production constraints for tomato (Solanum lycopersicum L.) due to unfavorable, above optimum temperatures. This research was undertaken to evaluate growth and fruit yield of tomato genotypes under three contrasting growing conditions (i.e., optimal temperature in field-, high temperature in field- and high temperature in greenhouse conditions) to determine their relative heat tolerance. Eleven tomato genotypes, including two local check varieties, were evaluated, and data on growth and yield were measured and analyzed. The interactions between the genotypes and growing conditions for all yield traits were significant. In general, the performance of tomato under optimal temperature field conditions was better than under high temperature field- and greenhouse conditions. Genotypes CLN1621L, CLN2026D, CLN3212C, and KK1 had consistently greater fruit yield per plant in all growing conditions. Although the local genotype, Neang Tamm, had lower yield under optimal conditions, it performed moderately well under high temperature field- and high temperature greenhouse conditions, and yield decrease under high temperature condition was minimal. Genotype CLN1621L had stable fruit setting compared to other genotypes under high temperature conditions. Since fruit setting and yield are important traits for heat tolerance, genotypes CLN1621L and Neang Tamm are potential candidates for breeding programs focused on improved yield and heat stress tolerance.

This study was conducted using four soil treatments (0, 22.5, 45 and 90 mg SO 2À 4 kg À1 ) with balanced amounts of nitrogen (N), phosphorus pentoxide (P 2 O 5 ) and potassium oxide (K 2 O) for each treatment, provided using ammonium phosphate sulfate (42% of sulfate), rock phosphate, potassium chloride and urea. These treatments were employed in incubation and jar experiments to investigate methane (CH 4 ) production, redox potential (Eh) and pH of the soil. The same treatments were also used in potted soil planted with rice (Oryza sativa L.). In addition, urea-excluded treatments were also included in the incubation and jar experiments. The results showed that the presence of sulfate (SO 2À 4 ) reduced CH 4 production from the incubation experiment. Treatments excluding urea produced larger amounts of CH 4 than urea-amended ones. In the jar experiment, the soil Eh decreased from 486 to À412 mV with increased duration of flooding. In general, the presence of SO 2À 4 delayed the drop of Eh. The submerged soil with the highest amount of SO 2À 4 at 90 mg SO 2À 4 kg À1 had the lowest pH compared to other treatments. In a subsequent pot experiment, riceplanted soil showed that CH 4 emission was suppressed through the growing period with increasing SO 2À 4 content of 45 and 90 mg SO 2À 4 kg À1 . This suppressing effect of increasing SO 2À 4 application was clearly shown at the early growing period. The results suggest that sulfate has the potential to mitigate methane production and emission from paddy soil. However, the effects of high sulfate levels on rice yields need further study in the paddy field.

Nitrogen (N) and phosphorus (P) deficiencies are key constraints in rainfed lowland rice (Oryza sativa L.) production systems of Cambodia. Only small amounts of mineral N and P or of organic amendment are annually applied to a single crop of rainfed lowland rice by smallholder farmers. The integration of leguminous crops in the pre‐rice cropping niche can contribute to diversify the production, supply of C and N, and contribute to soil fertility improvement for the subsequent crop of rice. However, the performance of leguminous crops is restricted even more than that of rice by low available soil P. An alternative strategy involves the application of mineral P that is destined to the rice crop already to the legume. This P supply is likely to stimulate legume growth and biological N2 fixation, thus enhancing C and N inputs and recycling N and P upon legume residue incorporation. Rotation experiments were conducted in farmers' fields in 2013–2014 to assess the effects of P management on biomass accumulation and N2 fixation (δ15N) by mungbean (Vigna radiata L.) and possible carry‐over effects on rice in two contrasting representative soils (highly infertile and moderately fertile sandy Fluvisol). In the traditional system (no legume), unamended lowland rice (no N, + 10 kg P ha−1) yielded 2.8 and 4.0 t ha−1, which increased to 3.5 and 4.7 t ha−1 with the application of 25 kg ha−1 of urea‐N in the infertile and the moderately fertile soil, respectively. The integration of mungbean as a green manure contributed up to 9 kg of biologically fixed N (17% Nfda), increasing rice yields only moderately to 3.5–4.6 t ha−1. However, applying P to mungbean stimulated legume growth and enhanced the BNF contribution up to 21 kg N ha−1 (36% Nfda). Rice yields resulting from legume residue incorporation (“green manure use”–all residues returned and “grain legume use”–only stover returned) increased to 4.2 and 4.9 t ha−1 in the infertile and moderately fertile soil, respectively. The “forage legume use” (all above‐ground residues removed) provided no yield effect. In general, legume residue incorporation was more beneficial in the infertile than in the moderately fertile soil. We conclude that the inclusion of mungbean into the prevailing low‐input rainfed production systems of Cambodia can increase rice yield, provided that small amounts of P are applied to the legume. Differences in the attributes of the two major soil types in the region require a site‐specific targeting of the suggested legume and P management strategies, with largest benefits likely to accrue on infertile soils.

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Locally-available materials could be used to address soil fertility constraints. Vermicomposting is a promising technology where various organic materials are converted into processed compost by earthworms. This study evaluated local feed sources and their potential for vermicompost production. The vermicompost production was carried out in the plastic container under a roofed and net-sided production house. The plot design was laid out in Completely Randomized Design (CRD) with nine replications. Vermiculture feedstock treatments were cow manure (CM) and three cow manure and alternative feed stock treatments (75:25 on a dry basis) that included water hyacinth (WH), used coffee grounds (coffee), or Azolla. The results showed that cow manure combined with Azolla tended to produce more vermicompost after four weeks, but post-harvest earthworm weight was lower. The cow manure treatment produced higher earthworm weights. However, the earthworm population was not influenced by feed sources. The chemical characteristics of vermicompost were not different among feed source ratios or combination. A comparison of the feed stock material before and after vermiculture composting show that EC and total P increased in the compost, total K, organic C and the C:N ratio decreased, but pH and Total N remained constant.