Prediction of grain yield and nitrogen uptake by basmati rice through in-season proximal sensing with a canopy reflectance sensor

Precision Agriculture - The present study was conducted to establish prediction models for grain yield and nitrogen (N) uptake using normalized difference vegetation index (NDVI) measurements with...     

Calibrating the leaf colour chart for need based fertilizer nitrogen management in different maize (Zea mays L.) genotypes

Large field to field variability restricts efficient fertilizer N management when broad based blanket recommendations are used in maize (Zea mays L.). To achieve higher yields and to avoid nitrogen (N) deficiency risks, many farmers apply fertilizer N in excess of crop requirement in maize. Field experiments were conducted for five years (2005–2009) to establish and evaluate threshold leaf colour to guide in-season need based fertilizer N topdressings in four maize genotypes. Colour (of the first top maize leaf with fully exposed collar) as measured by comparison with different shades of green colour on a leaf colour chart (LCC) and maize grain yield was significantly correlated. The Cate–Nelson plot of chlorophyll (SPAD) meter/leaf colour chart values against relative grain yield of 0.93 for the experiments conducted during first two years indicated that LCC shade 5 during vegetative growth stages and LCC shade 5.5 at silking stage (R1) can guide crop demand driven N applications in maize. Evaluation of the established threshold leaf greenness during the next three years revealed that fertilizer N management using LCC 5 starting from six-leaf (V6) stage to before R1 stage resulted in improved agronomic and N recovery efficiency in different maize genotypes. There was no response to fertilizer N application at R1 stage. The study revealed that in maize, fertilizer N can be more efficiently managed by applying fertilizer N dose based on leaf colour as measured by LCC than blanket recommendation.     

Poultry litter as a nitrogen and phosphorous source for the rice–wheat cropping system

Poultry litter (PL) is an important nutrient source; however, no information is available regarding its value in supplying N and P in rice–wheat (RW) production. A three-year field study was conducted at Ludhiana, Punjab, India on a loamy sand soil to identify optimum combination of PL and N and P fertilizers for a sustainable RW production. The litter was applied to rice at 5 Mg ha⁻¹ as a single application and supplemented with different rates of N. The residual effect of PL and the direct effects of the different combinations of N and P were studied in the following wheat. Nitrogen and P mineralization from PL was studied under controlled conditions in the laboratory, and macronutrient input–output balances were estimated from field results. About 46% of the N from PL was released after 60 days of incubation. The release of P from the PL occurred mainly during the initial 20 days after incubation, accounting for 15–17% of the total P. Combining PL with fertilizer N (40 kg ha⁻¹) increased rice yield and nutrient uptake similar to what was obtained with the application of recommended fertilizer N (120 kg ha⁻¹). In the following wheat, the residual effect of PL was equal to 30 kg N ha⁻¹ and 13 kg P ha⁻¹. After three annual cropping cycles and PL application, mean soil organic C increased by 17%, Olsen-P by 73%, and NH₄OAc-extractable-K by 24%. Most treatments had positive P but negative K balances. About 11% of the net P balance was recovered from the soil as Olsen-P. The study showed that optimum N and P fertilizer doses for an RW system receiving 5 Mg ha⁻¹ of PL are 40 kg N ha⁻¹ for rice and 90 kg N + 13 kg P ha⁻¹ for the following wheat. Safe and effective management of PL should be based on P balance, particularly when regular applications of PL are to be made in the RW system.