Kunnika Naklang

Growth of rice cultivars by direct seeding and transplanting under upland and lowland conditions

Abstract Rainfed rice crops are grown under both upland and lowland conditions. While upland crops are almost always direct seeded, both transplanting and direct seeding are commonly practiced for lowland crops in Asia. Direct seeding may be by broadcasting or dibbling. The effects of these various rice cultural practices on shoot and root growth and grain yield were examined using four contrasting cultivars in each of three years at Surin, Northeast Thailand. Under upland conditions, no yield was obtained under severe drought in two of the three years and yield was less than half that under lowland conditions in the third year. Lowland crops did not suffer water stress. Under lowland conditions, direct-seeded crops yielded more than transplanted crops in one year, slightly less in another when establishment was a problem in direct seeding, and similar between the two methods in the other. Direct seeding, particularly broadcasting, produced more total dry matter than transplanting. Root dry-matter growth was small after panicle initiation under all conditions, and was greater in direct seeding than transplanting in lowland conditions. Root growth occurred mostly in the top 10 or 15 cm soil layer in both upland and lowland crops. Root mass below 30 cm depth exceeded 10% of the total root mass at maturity in only one crop in which seeds were dibbled under upland conditions. Cultivar differences in root growth were generally small among all experiments. One notable exception was high root mass near the soil surface for IR20, a cultivar suitable for irrigated conditions, when transplanted under lowland conditions. Although shoot growth was also similar among cultivars, there were often significant cultivar differences in grain yield. The highest yield was produced by IR57514-PMI-5-B-1-2, a semi-dwarf cultivar that produced a large number of panicles in most experiments.

Growth and grain yield of contrasting rice cultivars grown under different conditions of water availability

Abstract Rice crops are susceptible to drought, which causes large yield losses in many Asian countries. The development of drought-resistant cultivars may be assisted if mechanisms of drought resistance are known. This work was carried out to elucidate how some rice cultivars achieve higher yield than others under water-limiting conditions. A total of 11 experiments were conducted in northeast Thailand, and four contrasting cultivars were compared in each experiment for phenological development, dry matter growth, leaf death, grain yield and yield components. High-yielding cultivars were generally short statured and had high harvest index, and they tended to perform better than others in all conditions of water availability. When drought developed during late growth stages, early flowering to escape water stress was an important character. During late drought some cultivars were able to retain green leaves longer than others and increased dry matter when others stopped growing. It is thus concluded that cultivars suitable for rainfed conditions are those with high yield potential resulting from high harvest index under favourable growing conditions, appropriate flowering time to escape severe water stress that commonly develops after the end of the rainy season, and an ability to maintain growth during drought so that yield determining processes can be completed with minimum disturbance.

The management of rice straw, fertilisers and leaf litters in rice cropping systems in Northeast Thailand

The maintenance of soil organic matter (SOM) and the balancing of nutrient flows into and out of the rainfed rice cropping systems in Northeast Thailand is of paramount importance to arresting the decline in soil fertility and crop yields. A system where small applications of leaf litters from locally grown trees are applied annually to rice paddy soils prior to transplanting is described. The annual application of 1500 kg/ha of Cajanus cajan, Acacia auriculiformis, Phyllanthus taxodifolius and Samanea saman for five seasons resulted in increases in rice grain yield of 48, 35, 32 and 23% above the no-leaf litter control, respectively. Average annual nutrient inputs from the leaf litters, in kg/ha, ranged from 62.7 N, 3.9 P, 17.9 K, and 3.5 S for Cajanus cajan to 24.5 N, 1.5 P, 8.1 K and 2.0 S for Acacia auriculiformis. Nutrient balances, determined by the difference between the inputs (fertiliser and added leaf litters) and outputs (grain and straw) indicated net positive N and P balances of up to 457 and 60 kg/ha. respectively, after five seasons of leaf litter applications. Sulfur and potassium balances resulted in net deficits of up to −3 and −52 kg S and K/ha, respectively, where no leaf litter was applied and rice straw was removed following harvest. Calculated apparent nutrient recoveries reflected the decomposition rate of the added residues and were highest for P and K, reflecting their higher soil residual value than mobile nutrients such as N and S. Sustainable farming systems will require that crop yields are stable through the maintenance of soil fertility and the balance of nutrients in the system.

Soil-Quality Indicators for Predicting Sustainable Organic Rice Production

Soil physical, chemical, and biological properties in a rice field located at the Surin Rice Research Center, Thailand, were evaluated as indicators for predicting organic rice (Kao Dok Mali 105 variety) production and yield. Four treatments under different management practices were studied. They included (1) conventional farming (CF) receiving chemical fertilizer application; (2) organic plot receiving green manure (GM) addition; (3) organic plot receiving rice straw (RS) addition; and (4) control plot (CT) without any external plant nutrient source. Soil quality in the four treatments was assessed based upon selected physical, chemical, and biological parameters. Key findings are as follows: cation exchange capacity (CEC), electrical conductivity (EC), pH, soil organic matter (SOM), and essential macronutrients [nitrogen (N), phosphorus (P), and potassium (K)] were low in all plots. Soil biological properties including potential N mineralization (PMN), soil basal respiration (BR), microbial biomass carbon (MBC) and microbial biomass N (MBN) in all treatments were also low. Principal component analysis (PCA), using 15 soil properties, showed significant differences among farm management practices. Soil chemical and biological properties best related to soil quality included P, N, and SOM (for chemical properties) and MBC, MBN, and BR (for biological properties). Based on significant relationships between yield (r > 0.75) and the soil properties (r > 0.55), selected soil biological (MBC, MBN, and BR) and chemical (TOP [total organic phosphorus], TK [total potassium], TN [total nitrogen], SOC [soil organic carbon], and SOM) properties were determined to be suitable soil-quality indicators, respectively. A soil-quality indicator for predicting rice yield was computed using multiple regression analyses. The regression model (Y = −1.685 + 0.333 (MBN) + 0.640 (TK) − 0.282 (SOC), r2 adjusted = 0.962) was used for predicting yield. Grain yield of rice (RMSE = 0.046 t ha−1, D index = 0.45) was obtained using this regression model.