Assessing the Effect of Seedling Age and Time of Urea Supergranule Application on Rice Growth, Yield and Nitrogen Use efficiency

Nitrogen is the most limiting nutrient in tropical soils and nitrogen fertilizer application to rice is subject to losses. Good synchrony of nitrogen availability to crop’s need is a strategy to reduce losses and improve efficiency. A pot experiment was conducted to assess the effect of seedling age and time of urea supergranule application on rice growth, yield and nitrogen use efficiency. The experiment consisted of 10, 14, 21 and 28-day old seedlings and urea supergranule applied at 0, 7, 14 and 21 days after transplanting with a check treatment without nitrogen application. Results indicated significant effect of seedling age on growth, yield and nitrogen use efficiency. Highest grain yield, nitrogen uptake, agronomic use efficiency of nitrogen and nitrogen recovery efficiency were obtained with 10 and 14-day old seedlings, while the lowest values were observed for 28-day old seedlings. Urea supergranule applied at 7 or 14 days after transplanting gave the highest rice growth parameters while the lowest performances were obtained with urea supergranule applied at 0 and 21 days after transplanting. The interactive effect showed better growth, yield and nitrogen use efficiency of rice when urea supergranule was applied at 7 or 14 days after transplanting seedlings of 10 and 14-day old. The results suggested that even though application of urea supergranule at 7 and 14 days after transplanting increased rice yield over 0 and 21 days after transplanting, for the aged seedlings of 21 and 28-day old, the variation of urea supergranule application time could not compensate for the decrease of yield due to old seedlings transplanting

Phosphorus adsorption, rice dry matter yield, and P use efficiency as influenced by phosphorus fertilizer rates in rainfed lowland soils in Togo

The study focused on improving phosphorus (P) fertilizer recommendation in rainfed lowland rice soils in Togo. Phosphorus adsorption was conducted on four soils to determine their P adsorption characteristics and standard phosphorus requirement (SPR). The adsorption maximum ranged from 143 to 200 mg P/kg. The amount of P adsorbed range from 62.70 to 74.85 mg P/kg. Greenhouse experiment was conducted to determine rice response to phosphorus rates based on the SPR values, and to assess rice P uptake and use efficiency. Five phosphorus rates, Control: 0 mg P kg−1, P recommended rate (RR): 5 mg P kg−1, 4 × RR: 20 mg P kg−1, 50% SPR and 100% SPR were used. Results indicated no significant difference between the Control treatment and the P recommended rate (RR), and between the 50% SPR and the 100% SPR with reference to shoot dry matter yield. P uptake and P use efficiency were significantly and positively influenced by the various P fertilizer rates. From the study, the blanket P recommended rate is inappropriate, however, site-specific P fertilizer rate of 50% SPR may be recommended to improve rainfed lowland rice yields in Togo

Yield-limiting macronutrients for rice in sub-Saharan Africa.

Nutrient deficiencies are considered major constraints to rice production in sub-Saharan Africa (SSA), but a systematic, continent-wide analysis of these constraints is lacking. The objective of this study was to assess responses of rice yields to macronutrients (N, P, and K) across major rice production systems [irrigated lowland rice (IL), rainfed lowland rice (RL), and rainfed upland rice (RU)] and diverse agro-ecological zones (semi-arid, sub-humid, humid, and highlands) in SSA. Diagnostic trials were conducted in 17 countries in 18–60 farmers' fields in each of 30 sites (totaling 1037 farmers' fields), of which 12 sites were in IL, 15 in RL and 3 in RU. All trials had an NPK treatment, and three treatments in which either nitrogen (N), phosphorus (P), or potassium (K) was omitted from the NPK treatment (minus N, P, and K plots). The trials were conducted during one or two seasons. Regression between yields in the NPK and minus N plots was used for calculating N fertilizer requirement, following the approach used for the development of a nutrient management decision support tool for rice (RiceAdvice) in SSA. Site mean yields in the NPK treatment ranged from 1.4 to 7.3 t ha−1. On average, these yields were 1.1 t ha−1 higher than farmers' yields previously observed in the same sites. N was generally the most limiting nutrient, followed by P. Rice yields without N, P, and K were 68, 84, and 89% of yields in the NPK treatment, and were positively correlated with those in the NPK treatment irrespective of production systems and agro-ecological zone (AEZ). Results from a regression model across sites indicated that achieving 3, 5, and 7 t ha−1 requires N fertilizer application at an average rate of 56, 91, and 122 kg N ha−1, respectively. However, there was significant treatment by site interaction on rice yield. Site mean yields were significantly lower without N, P, and K in 93, 60, and 50% of sites as compared to the NPK treatment. Yield response to macronutrients varied across sites and was not related to production system, nor AEZ. Results from this study will help further improvement of RiceAdvice for providing decision support tailored to the particular site, zone, or production system, thereby closing yield gaps, improving fertilizer nutrient efficiency and preventing negative environmental consequences of fertilizer use

Variability and determinants of yields in rice production systems of West Africa

Rice (Oryza spp.) is the major staple food for most countries in West Africa, but local production does not meet demand. Rice is grown mainly by smallholder farmers, and yields are generally low with high temporal and spatial variability. Low yields have been attributed to unfavorable climate conditions, poor soil quality, and sub-optimum agricultural practices. The objectives of this study were to assess variation in yields of three major rice production systems (irrigated lowland, rainfed lowland, and upland) across three climatic zones (semi-arid, sub-humid, and humid), and identify factors affecting that variation. We analyzed data on yield, climate, soil, and agricultural practices for 1305 farmers’ fields at 22 sites in 11 West African countries between 2012 and 2014. A boundary function approach was used to determine attainable yields. Random forest algorithm was used to identify factors responsible for yield variation. Average rice yield was 4.1, 2.0, and 1.5 t ha−1 in irrigated lowland, rainfed lowland, and rainfed upland systems, respectively, with maximum attainable yields of 8.3, 6.5, and 4.0 t ha−1. Yield difference between attainable and average yield tended to be higher in irrigated and rainfed lowland systems. In those two systems, yields were highest in the semi-arid zone, while no difference in yields among climatic zones was apparent for upland rice. High rice yields were associated with high solar radiation, high maximum temperature, intermediate air humidity, multiple split nitrogen (N) fertilizer applications, high frequency of weeding operations, the use of certified seeds, and well-leveled fields in the irrigated lowland system. Minimum temperature, solar radiation, rainfall, construction of field bunds, varietal choice, and the frequency of weeding operations were determinants of rice yield variation in the rainfed lowland system. Varietal choice, bird control, and frequency of weeding operations affected rice yields in the upland system. Improving access to inputs, improving input use efficiencies, and site-specific management strategies are recommended as priority interventions to boost rice yields at regional scale independent of production system and climatic zone