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Groundnut as a pre-rice crop is usually harvested 1-2 months before rice transplanting, during which much of legume residue N released could be lost. Our objectives were to investigate the effect of mixing groundnut residues (GN, 5 Mg ha À1 ) with rice straw (RS) in different proportions on: (i) regulating N dynamics, (ii) potential microbial interactions during decomposition, and (iii) associated nitrous oxide and methane emissions at weekly intervals during the lag phase until rice transplanting (i, ii) or harvest (iii). Decomposition was fastest in groundnut residues (64% N lost) with a negative interaction for N loss when mixed 1:1 with rice straw. Adding groundnut residues increased mineral N initially, while added rice straw led to initial microbial N immobilization. Mineral N in mixed residue treatments was significantly greatest at the beginning of rice transplanting. Soil microbial N and apparent efficiency were higher, while absolute and relative microbial C were often lowest in groundnut and mixed treatments. Microbial C:N ratio increased with increasing proportion of added rice straw. N 2 O losses were largest in the groundnut treatment (12.2 mg N 2 O-N m À2 day À1 ) in the first week after residue incorporation and reduced by adding rice straw. N 2 O-N emissions till rice harvest amounted to 0.73 g N 2 O-N m À2 in the groundnut treatment. CH 4 emissions were largest in mixed treatments (e.g. 155.9 g CH 4 m À2 , 1:1 treatment). Mixing residues resulted in a significant interaction in that observed gaseous losses were greater than predicted from a purely additive effect. It appears possible to regulate N dynamics by mixing rice straw with groundnut residues; however, at a trade-off of increased CH 4 emissions.

The information on genotypic responses to the seasonal variation in the starch content, starch yield, and starch quality of cassava is limited. The objective of this research was to investigate the seasonal variation of starch characteristics of three cassava genotypes grown under irrigation. The experiment was conducted at four planting dates (20 April, 30 June, 5 October, and 15 December 2015). Three cassava genotypes (CMR38-125-77, Kasetsart 50, and Rayong 11) were evaluated in a randomized complete block design with four replications and the plants were harvested at 12 months. The planting date contributed the largest portion of the total variation in the starch content, starch yield, and starch granule size. The amylose content variability was heavily influenced by genotype. Cassava planted on 5 October or 15 December had greater starch content, starch yield, and starch granule in most genotypes. This was likely due to a higher temperature and solar radiation during the 3–9 months post-planting. CMR38-125-77 showed a consistently high starch content, starch yield, and high amylose content for most planting dates except for the starch yield on 20 April, of which Rayong 11 was the best. These findings will be useful for choosing suitable cassava genotypes for different growing seasons and for facilitating breeding efforts for high starch-yielding and high-quality cassava starch in the future.

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The objective of this study was to investigate the responses of peanut genotypes to midseason drought, regarding in particular nutrient uptakes and their correlations with biomass production and pod yield. The experiment was conducted during the dry seasons of 2011/12 and 2012/13. Five peanut genotypes with different levels of drought tolerance and 2 water regimes (well-watered and midseason drought) were laid out in a split-plot design with 4 replications. Midseason drought was imitated by stopping irrigation at 30 days after planting (DAP) and then rewatering at 60 DAP. The data were recorded for contents of N, P, K, Ca, and Mg in plant tissues, biomass production, yield components, and pod yield at harvest. The results showed that midseason drought significantly reduced the uptake of all nutrient elements. Peanut genotypes with higher levels of drought tolerance took up more nutrients than those with lower levels. The uptake of all nutrient elements contributed to biomass production, pod yield, and the number of pods per plant. ICGV 98305 was the best genotype with the highest uptakes of all observed nutrient elements.

It was hypothesized that the application of eucalyptus biochar enhances nutrient use efficiencies of simultaneously supplied fertilizer, as well as provides additional nutrients (i.e., Ca, P, and K), to support crop performance and residual effects on subsequent crops in a degraded sandy soil. To test this hypothesis, we conducted an on-farm field experiment in the Khon Kaen province of Northeastern Thailand to assess the effects of different application rates of eucalyptus biochar in combination with mineral fertilizers to upland rice and a succeeding crop of sugarcane on a sandy soil. The field experiment consisted of three treatments: (1) no biochar; (2) 3.1 Mg ha -1 biochar (10.4 kg N ha -1 , 3.1 kg P ha -1 , 11.0 kg K ha -1 , and 17.7 kg Ca ha -1 ); (3) 6.2 Mg ha -1 biochar (20.8 kg N ha -1 , 6.2 kg P ha -1 , 22.0 kg K ha -1 , and 35.4 kg Ca ha -1 ). All treatments received the same recommended fertilizer rate (32 kg N ha -1 , 14 kg P ha -1 , and 16 kg K ha -1 for upland rice; 119 kg N ha -1 , 21 kg P ha -1 , and 39 kg K ha -1 for sugarcane). At crop harvests, yield and nutrient contents and nitrogen (N) use efficiency were determined, and soil chemical properties and pH 0 monitored. The eucalyptus biochar material increased soil Ca availability (117 28 and 116 7 mg kg -1 with 3.1 and 6.2 Mg ha -1 biochar application, respectively) compared to 71 13 mg kg -1 without biochar application, thus promoting Ca uptake and total plant biomass in upland rice. Moreover, the higher rate of eucalyptus biochar improved CEC, organic matter, available P, and exchangeable K at succeeding sugarcane harvest. Additionally, 6.2 Mg ha -1 biochar significantly increased sugarcane yield (41%) and N uptake (70%), thus enhancing N use efficiency (118%) by higher P (96%) and K (128%) uptake, although the sugar content was not increased. Hence, the application rate of 6.2 Mg ha -1 eucalyptus biochar could become a potential practice to enhance not only the nutrient status of crops and soils, but also crop productivity within an upland rice-sugarcane rotation system established on tropical low fertility sandy soils.

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