Simulating the potential effects of reducing runoff and planting date on sorghum yields in Botswana

Extremely variable climatic conditions cause Botswana farmers to plant after each significant rain. Various management techniques, such as double ploughing, have been proposed to reduce runoff and increase sorghum yields. SORKAM, a computer growth model for sorghum, was used to estimate the potential effects of the reduced runoff effect of double ploughing on sorghum yields and yield stability for four locations (six soils) and climatic data for 40 years. Simulated reduced runoff increased sorghum yields up to 32% on a soil with about 50% clay. The smallest yield increase, 1%, was on a soil with 90% sand. Reduced runoff increased yields most on soils that have higher water holding capacities, allowing greater water storage. Although double ploughing, in general, would delay the first planting and early planting had higher average yields than late planting, no date of planting was optimum and ranges in yield were great for all dates. Cumulative frequency distributions showed that the advantage of reduced runoff not only was dependent on location (water holding capacity) but also on yield level. At all locations at low yield levels, reduced runoff either decreased yield or inceased the incidence of total crop failure.Les conditions climatiques etant extrement variables permettent aux agriculteurs du Botswana de planter apres chaque pluie abondante. Les techniques des gestions variees, par exemple, le systeme de labourer deux fois a ete propose pour reduire la carence et l'augmentation en production de sorgho. Le modele de l'augmentation du sorgho qui est connu sous le nom de SORKAM, etait utilise pour estimer les effets du potentiel de la reduction de l'effet de la carence du systeme de labourer deux fois sur la stabilite de production du sorgho pour quatre locations (six sols) et les donnees des climats pour une duree de 40 ans. La reduction de carence simultanee a augmentee la production du sorgho a 32% et sur le sol a peu pres de 50% d'argile. La plus petite augmentation de production sur les sols ont de grandes capacites de conserver de l'eau, qui occasionne le stockage d'une grande quantite d'eau. En general, malgre le double systeme de labourer ce qui retarde le premiere saison de planter tot a une moyenne des productions par rapport au planter tot, aucune date de planter n'etait optimum et les variations en production etaient superieures par rapport a toutes les dates. les distributions des frequences cumulatives ont montrees que l'avantage de carence reduite n'etait par seulement dependante en location (capacite de conserver de l'eau), Mais aussi au niveau de production. Dans toutes les locations aux bas niveau de production, a reduit la carence soit diminuer, l'incidence totale de l'echec de la plante

Assessing climatic risk to sorghum production in water-limited subtropical environments. II.Effects of planting date, soil water at planting, and cultivar phenology

Rainfed crop production in the subtropics is a risky enterprise due to high rainfall variability. When planting opportunities occur, farmers face risky choices because the consequences of decisions made at planting are uncertain. This paper presents a general approach to generating the information required to assistt in making planting decisions in climatically variable subtropical environments. The approach involved coupling a sorghum growth simulation model to long-term sequences of climatic data to provide probabilistic estimates of yield for the range of decision options, such as planting time and cultivar maturity, for a range of soil conditions. The likely change in the amount of stored soil water with delay in planting was also simulated to account for the decision option of waiting for a subsequent planting opportunity. The approach was applied to three locations (Emerald, Dalby and Roma) in subtropical Australia. Production risk varied with location, time of planning, soil water storage, and cultivar phenology. Yield responses to these factors were associated closely with differences in leaf area development and degree of depletion of the water resource. The probabilistic estimates of yield and change in stored soil water provided in this paper can assist decision-makers with risky choices at planting in subtropical environments. Such information can be used in decision analysis or in computerized decision support, where decision-makers, and their risk preferences, can interact directly with the information

Crop Rotation and Soil Amendment Alters Sorghum Grain Quality

Soybean [Glycine max (L.) Merr.] rotation enhances grain sorghum [Sorghum bicolor (L.) Moench] yield, but infl uence on grain quality has not been measured. The objective was to determine the effect of cropping sequence (CS) and soil amendment (SA) on grain yield and quality. Sorghum grain yield and quality, soil NO3–N and water were measured in a rotation study in 2003 and 2004 on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll). Cropping sequences were continuous sorghum, and sorghum rotated with non-nodulating and nodulating soybean. Soil amendments consisted of no amendment, manure (17–26 Mg dry matter ha−1 yr−1), and N (84 kg ha−1 yr−1). CS × SA interaction effects were found for most parameters. Rotation with non-nodulating soybean without SA increased yield by 2.6 to 2.8 Mg ha−1 over continuous sorghum without SA. Rotation without SA with nodulating soybean further increased yield by 1.7 to 1.8 Mg ha−1 over rotation with non-nodulating soybean. Grain N increased by 0.5 to 1.0, 2.5 to 5.0, and 3.3 to 4.9 g kg−1 for N application to continuous sorghum and sorghum rotated with non-nodulating and nodulating soybean, respectively. Tangential abrasive dehulling device (TADD) removal indicated that continuous sorghum without SA produced the softest grain with 43 to 44% TADD removal, and sorghum rotated with nodulating soybean with manure produced the hardest grain with 22 to 27% TADD removal. As food end-use opportunities for sorghum grain evolve, use of crop rotation and SA application will be important to produce grain with desirable quality attributes. Includes corrected Table 4